PubMed Central

**PubMed Central Overview:**
– PMC was proposed as E-biomed by Harold Varmus in 1999.
– Launched in February 2000, PMC aims to provide free access to biomedical research.
– PMC is a digital repository with over 5.2 million archived articles.
– Author-initiated deposits exceeded 103,000 papers from Jan 2013 to Jan 2014.
– About 4,000 journals participate in depositing content into PMC.
– PMC enriches articles with metadata, medical ontology, and unique identifiers.
– PMC allows linking to other NCBI databases through Entrez search systems.

**PMC Adoption and Policies:**
– The NIH Public Access Policy promotes free access to NIH-funded research.
– The Consolidated Appropriations Act of 2008 mandated modifications to NIH policies.
– Many publishers cooperate with the NIH to provide free access to their works.
– Growth of PMC has been rapid due to collaborative efforts with publishers.
– Some publishers impose embargo periods on releasing articles on PMC.

**Technology and Distribution:**
– Articles sent to PMC in XML or SGML format from publishers.
– NLM Journal Publishing DTD is commonly used by publishers.
– In-house indexing system provides search capability for PMC.
– PMC exemplifies systematic external distribution by a third party.
– Some publishers prohibit third-party distribution as per contributor agreements.
– Embargoes on PMC range from a few months to a few years, with 6-12 months being common.

**Reception and Impact:**
– Mixed reactions from the scholarly publishing community regarding PMC.
– PMC supports open access publishers in disseminating biomedical knowledge.
– Positive reception from libraries, universities, and patient rights organizations.
– Open access papers show greater research impact in certain fields.
– Public repositories draw significant readership away from journal websites.

**PMC Identifiers and Related Initiatives:**
– PMCID is a bibliographic identifier for PubMed Central, distinct from PMID.
– PMCID format: PMC followed by a string of numbers.
– PMCID is required in NIH award applications and important for tracking articles.
– Related initiatives include Europe PubMed Central, CrossRef, and MEDLINE.
– NLM plays a crucial role in expanding access to scientific literature through PMC.