General Interest FAQs

FAQs for Journals Considering Participation in PMC

What is PubMed Central?

PubMed Central (PMC) is the U.S. National Institutes of Health (NIH) digital archive of biomedical and life sciences journal literature. Participation by publishers in PMC is voluntary, although participating journals must meet certain scientific and technical standards. PMC, itself, is not a publisher.

Access to the material in PMC is free, but use of the material still is subject to the copyright and/or related license terms of the respective authors or publishers. See the PMC Copyright Notice for more information.

Who operates PubMed Central?

PubMed Central was developed and is operated by the National Center for Biotechnology Information (NCBI), a division of the National Library of Medicine (NLM) at the U.S. National Institutes of Health (NIH).

Does any independent group oversee the operation of PubMed Central?

The PubMed Central National Advisory Committee, established in 1999, provides independent advice on the content and operation of PubMed Central. The Committee is responsible for establishing criteria for groups submitting material to the system, and ensuring that PubMed Central remains responsive to the needs of researchers, publishers, librarians, and the general public. Members of the Committee are appointed by the Director of the National Institutes of Health from the biomedical and information communities as well as the general public.

How long has PubMed Central been in existence?

PubMed Central began operating in February 2000 with content from two journals: PNAS: Proceedings of the National Academy of Sciences and Molecular Biology of the Cell.

What journals are currently available in PubMed Central?

See the PMC Journal List for a list of currently available journals.

How current is the material in PubMed Central?

The currency and age of material in PubMed Central varies by journal. Many journals make their content available in PMC as soon as it is published. Others may delay release of content in PMC for anywhere from a few months to more than a year after publication. Most journals provide free access to full text in PMC within a year of publication.

How far back in time does the archive reach?

NLM has digitized the earlier print issues of many of the PMC journals in order to provide online access to the complete run of issues of these journals. PMC has material dating back to mid- to late-1800s or early 1900s for some journals.

Does PubMed Central contain the complete contents of all the journals that are in its archive?

No. Journals that deposit their articles in PMC fall into one of three categories:

  1. For several hundred journals, PMC has the complete contents of each issue, starting with the first issue. For the older journals in this group, the back issues of a journal (generally, anything prior to the late 1990s) are available as digitized (scanned) copies of the original print journal.
  2. For a smaller group of journals, PMC has complete issues and volumes for recent years, but not for all the early years of the journal.
  3. For still other journals, PMC does not contain any complete issues, just a selection of articles, e.g., just those that are the result of NIH-funded research, or those that the journal has published as open access articles.

In all three categories, PMC contains a journal's final published version of the respective articles. The PMC Journal List includes information about what content is available from each journal, as well as links to that content.

In addition to the articles from these journals, PMC contains author manuscripts of selected articles from several thousand other journals. See Who may contribute to PubMed Central for more information. These manuscripts are accessible via a PMC search or a link from the corresponding PubMed abstract.

How can I find out when PubMed Central adds a new journal to its list or adds a large number of back issues for an existing journal?

If you add your name to the PMC News list, we will notify you by email whenever PMC makes these kinds of additions. Please use the link above to add your name to the list. Sending a “subscribe” email message to PMC will not work.

What is the connection between PubMed Central (PMC) and PubMed?

PubMed is a database of citations and abstracts for millions of articles from thousands of journals. It includes links to full-text articles at several thousand journal web sites as well as to most of the articles in PubMed Central.

PubMed Central (PMC) is an electronic archive of full-text journal articles, offering free access to its contents. PMC contains nearly 2 million articles, most of which have a corresponding entry in PubMed.

PubMed does not have citations for certain types of PMC material, such as book reviews, that are considered out of scope for PubMed. These items constitute a small portion of the total PMC collection and there are no plans to include them in PubMed.

How is PubMed Central related to UKPMC, PMC International, or portable PMC?

PMC International (PMCI) is a collaborative effort between NLM, the publishers whose journal content makes up the PMC archive, and organizations in other countries that share NLM's interest in archiving life sciences literature. The long term goal of PMCI is to create a network of digital archives that can share some or all of their respective locally deposited content with others in the network.

To date, NLM has authorized one PMCI center, UKPMC, which is sponsored by the Wellcome Trust and several other major UK research funders. UKPMC became operational in January 2007 and currently receives all its journal content directly from the U.S. PMC archive. Portable PMC (pPMC) is a version of the PMC software that has been developed by NCBI to enable PMCI sites such as UKPMC to display their content in a presentation style similar to the U. S. PMC site. Read more about PMCI and pPMC.

Are there any restrictions on the use of the material in PMC? Can I download a batch of articles from PMC for research or other purposes?

Although access to the material in PMC is free, the use of the material still is subject to the copyright and/or related license terms of the respective authors or publishers. See the PMC Copyright Notice for more information.

You may NOT use any kind of automated process to download articles in bulk from the main PMC site. PMC will block the access of any user who is found to be violating this policy. PMC does have two auxiliary services, the PMC OAI service and the PMC FTP service, that may be used to download certain articles in bulk. The PMC Open Access Subset page explains which articles are available through these services.

What is the PMC Open Access subset? Isn't everything in PMC open access?

The majority of the articles in PMC are subject to traditional copyright restrictions. They are free to access, but they are not Open Access articles in the specialized sense of that term.

The PMC Open Access Subset is a relatively small part of the total collection of articles in PMC. Articles in this subset are still protected by copyright, but are made available under a Creative Commons or similar license that generally allows more liberal redistribution and reuse than a traditional copyrighted work. See the PMC Open Access Subset page for more information on how you may retrieve and use these articles.

Who may contribute to PubMed Central?

PubMed Central will accept material from any life sciences journal that meets NLM's standards for the archive. A journal must qualify on two levels: on the scientific and editorial quality of its content, and on the technical quality of its digital files. See Add a Journal to PMC for details.

In addition, PMC will accept individual author manuscripts that are deposited via the NIH Manuscript Submission (NIHMS) system or a similar manuscript processing system. This route is available only for manuscripts that are covered by the public access policies of certain approved funding agencies, e.g., the NIH, the Wellcome Trust and other members of the UKPMC Funders Group, or the Howard Hughes Medical Institute.

Does PubMed Central include research that has not been peer reviewed?

No, PubMed Central does not include any unreviewed research articles.

What types of material may be deposited in PubMed Central?

As an archive, PMC strives to collect and preserve everything that is published in a participating journal. It has a cover-to-cover digital copy of the early issues of a journal that came into PMC through NLM's Back Issue Digitization Project. For more recent material, which a journal must supply in XML or SGML form, PMC accepts any editorial content that can be represented accurately with the NLM Journal Publishing XML DTD or a compatible DTD. In this context, “editorial content” refers to articles and article-like items, including book reviews, news items and obituaries. PMC also accepts journal cover images and accompanying captions.

In general, a participating journal must deposit in PMC the final, published version of an article as it appears on the journal's own web site. However, in the instance where PMC serves as the repository for a funding agency's access program, PMC will accept an author's final, peer reviewed manuscript of an article. See Who may contribute to PubMed Central?

Journals also contain what may be classified loosely as administrative content — editorial board and staff lists, instructions to authors, notices and announcements, and advertisements. At present, such content usually is available only in print or on an html page on a journal's web site. Few, if any, journals have it in XML form. We are developing XML tagging guidelines so that the administrative content can be included in the PMC archive as well. In the meantime, PMC will accept certain administrative items, if the journal publishes them in an article form and can provide suitable full-text XML. For example, see the instructions to authors that the Journal of Virology publishes as an article in its first issue of the year.

At this time, PMC will not accept promotional material for pharmaceutical or other products, even if presented in the form of an article.

Does PubMed Central include articles written in languages other than English?

Almost all the material now in PMC is in English. A few journals in PMC publish material in more than one language. For instance, CMAJ, the Canadian Medical Association Journal, has articles in French and English. In this case, only the English material appears in PMC's primary presentation of an article — the html full-text display. However, the journal's PDF version of the article, which is also available in PMC, may contain material in French as well as English. For older issues of the journal, which have been scanned under NLM's digitization program, PMC has the complete contents of each issue. That includes articles published exclusively in French.

In order to provide fuller coverage of non-English language material, PMC must be able to ensure proper validation of the archival XML record in these languages. NLM is considering possible collaborations with national agencies in other countries, as well as other methods, to obtain the non-English language expertise needed to provide an adequate level of quality control for the PMC archive.

Where can I get more information about using PMC?

Please see the PubMed Central Help Manual.

What are a journal's options for depositing articles in PubMed Central?

A journal has three options for depositing articles in PMC. All three require the completion of a formal participation agreement with NLM and the deposit of full-text XML and associated files for the final published version of the articles. The PMC participation agreements that correspond to these options are:

  • Full Participation: the journal commits to depositing the complete contents of each issue or volume, starting with a particular volume/issue or publication date.
  • NIH Portfolio: the journal commits to depositing all NIH-funded articles (as defined by the NIH Public Access Policy), starting with a particular volume/issue or publication date. The journal may choose to also deposit other, non-NIH-funded articles.
  • Selective Deposit: generally used by publishers who offer a hybrid publishing model, i.e., a traditional subcription-based journal in which only selected articles are made open access. These journals deposit just their open access articles in PMC.

See Add a Journal to PMC for the details of these agreements and the process of adding a journal to PMC.

Author manuscripts can not be deposited directly in PMC. Journals that wish to deposit manuscripts to help their authors comply with the NIH Public Access Policy should refer to the description of submission methods on the Public Access site.

How soon after publication must articles be made available through PubMed Central?

Journals are encouraged to make their content viewable in PMC at the time of publication, or soon after, but may choose to delay release in PMC for up to a year or more. See the Deposit and Access Policies for further guidelines on acceptable delay periods.

Who controls copyright privileges for the material archived in PubMed Central?

Copyright to all material deposited in PMC remains with the publisher or individual authors, whichever is applicable. PMC is simply an archive and does not claim copyright on any material in the archive.

Can publishers continue to provide journal content on other sites in addition to PMC?

A publisher participating in PMC is free to distribute its journal content in any other manner, including through other web sites. In fact, PMC will provide a publisher a copy of its content from the archive, at any time, to be used however the publisher chooses.

In what electronic formats may data be submitted to PubMed Central?

A journal must provide PubMed Central the full text of articles in an XML or SGML format that conforms to an acceptable journal article DTD (Document Type Definition). PMC does not accept articles in html format. The original high-resolution, digital image files must also be provided for all figures. A PDF version, if one exists, must be deposited in PMC in addition to the XML/SGML version (but not as the only form) of an article. Supplementary material, in the form of video, audio or data files that may be available with an article, must also be deposited.

Why does PubMed Central require the full text of every article in XML or SGML? Why do you not accept just a PDF or html file?

We believe that XML currently is the most effective archival format for the textual portion of a journal article. It essentially is software- and hardware-independent, and therefore adapts easily to changes in technology. XML lets you preserve the structure and meaning of an article in a relatively simple and human readable form.

With a well documented DTD, which serves as the "code book" for a piece of XML, you have something that people will still be able to decipher and use several generations from now, regardless of what technology is available then. This characteristic lends XML to being converted to a more advanced text recording format in the future. XML tagging also makes it easier to automatically parse the content of an article, which can help with more focused searching and with linking the article to related content in other databases, e.g., links to factual reference data.

The PMC archive is based on the NLM Journal DTD, which was created specifically for archiving digital journal content. It is well documented and increasingly is being adopted by other organizations in the field. PMC creates the html page for an article dynamically from the archival XML, every time that a user retrieves an article. In that respect, every request confirms that the archival copy is still functional.

Does PubMed Central have its own DTD? Must data be submitted in this format?

NLM has a Journal Publishing XML DTD that any journal may use to submit its data. PMC will also accept data in other full-text article DTDs that are widely used in life sciences journal publishing.

Must a journal include PDF versions of its articles in PubMed Central?

If a journal has PDF versions of its articles, NLM asks that they be deposited in the archive. A journal is not required to create PDFs solely for PubMed Central if it does not have them otherwise.

How can a journal be sure that PubMed Central will not alter the substance or meaning of submitted content?

PubMed Central does not change the content of submitted articles in any way. Experience to date suggests that participation in PMC may actually improve the quality of a journal's digital archival record, because PMC does an independent check of the accuracy of the XML/SGML and related files. The initial setup for a journal in PMC involves a thorough automated and manual review of the journal's content to ensure the accuracy of the material. The publisher is also asked to review its content in PMC before a journal is released to the public initially.

PMC's checking includes a comparison of the content in PMC to that at the journal's own web site and/or to the PDF version of the journal's articles. When discrepancies are found, the publisher is asked to provide corrected files to PMC, precisely because PMC does not want to make any changes to the publisher's content itself. Content deposited after the journal is live in PMC is verified and corrected in a similar manner.

PMC's approach to archiving adds a further, and significant, level of quality assurance. Every time a user asks to see an article in PMC, the online (html) view of that article is created on the spot, directly from a copy of the archival files — XML, image files, etc. PMC does not maintain a static html display of an article. Thus, every person who requests and reads an article in PMC is verifying the integrity of the archived files.

How much work is required of a publisher to prepare journal content for PubMed Central?

Many journals already create XML or SGML versions of their articles as part of the journal production process. These journals must only arrange to transmit their XML/SGML files to PMC together with associated image files and, as applicable, PDFs and supplementary data files. Some additional work may be needed, initially, to refine the journal's process for creating XML/SGML, if the submitted data does not satisfy PMC's technical standards..

A journal that does not currently produce XML or SGML versions of its articles would have to add this process to its production stream or contract with a vendor to create XML from the article source files.

What is the cost of participating in PubMed Central?

PubMed Central charges publishers nothing for including journal content in the PMC archive. A publisher is responsible for any costs it may incur in creating files that meet PMC's technical standards and transmitting them to PMC.

What does a journal gain by depositing its content in PubMed Central?

A journal gets the benefit of a permanent and freely accessible archive, managed by the National Library of Medicine, at almost no cost to the publisher — merely what it costs to provide PMC a copy of its material. Every journal can request from NLM and receive, free, a copy of its archived content at any time.

NLM's experience in digital journal archiving is evident in its development of the publicly available Journal Archiving and Interchange XML DTD. The DTD has been endorsed by the US Library of Congress and the British Library as a standard for digital journal archiving. It also has been adopted by a number of publishers and other archives. Continued development of the DTD and related tools is actively supported by an advisory committee of XML experts representing the publishing, archiving, and software development communities.

Participation in PMC usually improves the overall level of quality of a journal's archival files, as explained in the answer to a related FAQ. The journal also benefits from the integration of its full text with PubMed and the numerous other bibliographic and factual databases in NCBI's Entrez system, and the increased exposure that this brings.

Why is PubMed Central needed when many publishers already make their journals freely available on the web within a year of publication?

PubMed Central exists for two reasons, both of which arise from NLM's Congressional mandate: 1) to permanently preserve digital journal literature in the life sciences, and 2) to improve access to biomedical information for health professionals, researchers and the public.

PMC gathers the content from its diverse journal sources into a single repository, where it is stored in a uniform and well defined structured format, the NLM Journal Archiving and Interchange XML DTD. At the same time that PMC clearly maintains the identity of each journal, it also displays articles in a uniform style for users.

PMC's common archival format makes it easier to work with the material and extend its utility in efficient ways, using computational techniques. It allows greater integration of the literature with related resources, such as the variety of databases available in NCBI's Entrez system. New features can be applied consistently across the collection in a scalable manner. Once a technique has been developed, there is little extra cost to handle increased amounts of content. Experience has shown that this integration of information resources leads users to new knowledge and stimulates scientific discovery.

Why does PubMed Central require the deposit of complete articles, rather than linking to a journal site for full text?

NLM's journal abstract database, PubMed, already has links to full text at the online sites of thousands of journals that participate in the freely available LinkOut service. One of the primary goals of PMC is the creation of a digital archive of journal literature which, by definition, means the full text must be deposited in PMC. See the answers to the preceding questions to learn about some of the benefits of depositing content in PMC.

What kinds of links does PubMed Central provide from its site to a journal site?

PubMed Central displays a journal banner — a graphic supplied by the journal — at the top of every page that has content from the journal. Although the banner may not include commercial advertising, it can have links to various pages at the journal site. Some banners even provide a link from the full text of an article in PMC to the corresponding article at the journal site. See PLoS Biology, for example.

A journal also has the option to include a link from PMC's general PMC Copyright Notice to a more specific statement of terms and conditions of use posted on the journal site.

How are journal citations submitted to PubMed?

For a full participation journal, PMC will submit a citation to PubMed as soon as the article is live in PMC, after any publisher-specified embargo period. For an NIH Portfolio journal or a journal indexed in Medline, PMC will submit the citation as soon as the article is fully processed through our system, regardless of embargo. Please note that, for any non-Medline journal, only PMC can submit the journal's citations to PubMed. PMC may make an exception to this rule if a journal has no embargo. Citations usually appear in PubMed within 24 hours of submission.

What kinds of usage statistics does PubMed Central provide to participating journals?

Each publisher has password-controlled access to a web site that has usage reports for that publisher's journal(s). The reports, updated daily and aggregated by month, include counts of available articles, total access by type of page (table of contents, abstract, full-text html, PDF, etc.) unique IP addresses, and most frequently retrieved or cited articles. Line graphs of each measure supplement the reports.

Any report may be downloaded as a CSV file, for analysis with a spreadsheet package such as Microsoft Excel, or as an XML file. On request, PMC will also provide a publisher with a CSV file each month with usage for the month at the article level.

PMC's usage reports generally contain all information called for in the COUNTER specification, except that PMC does not report use by specific institutions. NLM's privacy policy prevents the reporting of use at an individual or organizational level.

Last updated: Tue, 21 Feb 2012