PubMed Central instance of bibliographic database
PubMed Central (PMC) is a free digital repository that archives open access full-text scholarly articles that have been published in biomedical and life sciences journals. As one of the major research databases developed by the National Center for Biotechnology Information (NCBI), PubMed Central is more than a document repository. Submissions to PMC are indexed and formatted for enhanced metadata, medical ontology, and unique identifiers which enrich the XML structured data for each article. Content within PMC can be linked to other NCBI databases and accessed via Entrez search and retrieval systems, further enhancing the public's ability to discover, read and build upon its biomedical knowledge.PubMed Central is distinct from PubMed. PubMed Central is a free digital archive of full articles, accessible to anyone from anywhere via a web browser (with varying provisions for reuse). Conversely, although PubMed is a searchable database of biomedical citations and abstracts, the full-text article resides elsewhere (in print or online, free or behind a subscriber paywall).
As of December 2018, the PMC archive contained over 5.2 million articles, with contributions coming from publishers or authors depositing their manuscripts into the repository per the NIH Public Access Policy. Earlier data shows that from January 2013 to January 2014 author-initiated deposits exceeded 103,000 papers during a 12-month period. PMC identifies about 4,000 journals which participate in some capacity to deposit their published content into the PMC repository. Some publishers delay the release of their articles on PubMed Central for a set time after publication, referred to as an "embargo period", ranging from a few months to a few years depending on the journal.  (Embargoes of six to twelve months are the most common.) PubMed Central is a key example of "systematic external distribution by a third party", which is still prohibited by the contributor agreements of many publishers.
type of example of manifestation of representation of