Overview and Size of PubMed Central
- PubMed Central (PMC) is a free digital repository for open access scholarly articles in biomedical and life sciences journals.
- PMC is developed by the National Center for Biotechnology Information (NCBI).
- Submissions to PMC are indexed and formatted for enhanced metadata, medical ontology, and unique identifiers.
- Content within PMC can be linked to other NCBI databases and accessed via Entrez search and retrieval systems.
- PMC is distinct from PubMed, which is a searchable database of biomedical citations and abstracts.
- As of December 2018, PMC contains over 5.2 million articles.
- Contributions to PMC come from publishers or authors depositing their manuscripts per the NIH Public Access Policy.
- From January 2013 to January 2014, author-initiated deposits exceeded 103,000 papers in a 12-month period.
- PMC identifies about 4,000 journals that participate in depositing their content.
- Some publishers have embargo periods before releasing articles on PMC.

History and Adoption of PubMed Central
- PubMed Central began as E-biomed, proposed by Harold Varmus in May 1999.
- The idea was inspired by the use of arXiv for preprints.
- The goal of E-biomed was to provide free access to all biomedical research.
- The proposal faced opposition from commercial publishers.
- The revised PubMed Central proposal received support from publishers and led to the creation of CrossRef and the DOI system.
- Launched in February 2000, PMC has grown rapidly.
- The NIH Public Access Policy aims to make NIH-funded research freely accessible.
- Many publishers are working cooperatively with the NIH to provide free access to their works.
- The Consolidated Appropriations Act of 2008 required the NIH to modify its policies.
- The adoption of PMC has increased the availability of free access to biomedical research.

Role and Function of PubMed Central
- PMC serves as a digital archive of full articles accessible to anyone.
- It provides a platform for sharing and discovering biomedical knowledge.
- PMC facilitates linking to other resources and databases.
- The repository enhances metadata and medical ontology for each article.
- PMC is an example of systematic external distribution by a third party.

Technology and Workflow of PubMed Central
- Publishers send articles to PubMed Central in XML or SGML format, using various article DTDs.
- Received articles are converted to the NLM Archiving and Interchange DTD via XSLT.
- Graphics are converted to standard formats and sizes.
- Bibliographic citations are parsed and automatically linked to relevant resources.
- An in-house indexing system provides search capability and is aware of medical terminology.

Impact and Related Resources of PubMed Central
- Reactions to PubMed Central vary among the scholarly publishing community.
- Some view PubMed Central as a valuable partner for open access publishing, while others express concerns about diverted traffic and economic consequences.
- Public repositories like PubMed Central have been found to draw significant numbers of readers away from journal websites.
- Open access papers in certain fields have shown greater research impact.
- PubMed Central has received support from libraries, universities, and patient rights organizations.
- PMCID is a bibliographic identifier for articles in PubMed Central.
- It consists of 'PMC' followed by a string of numbers.
- Authors applying for NIH awards must include the PMCID in their application.
- Europe PubMed Central, JATS, MEDLINE, PMID, PubMed Central Canada, Redalyc, and SciELO are related resources.
- A report by Beck provides insights into PubMed Central as an XML-based archive.
- NIHMS Statistics offer information on article deposits.
- The official website of PubMed Central is hosted by the National Center for Biotechnology Information.
- Various references provide additional information and sources for further reading.