Taken from Wikipedia:
PubMed is a free search engine accessing primarily the MEDLINE database of references and abstracts on life sciences and biomedical topics. The United States National Library of Medicine (NLM) at the National Institutes of Health maintains the database as part of the Entrez system of information retrieval.
Each journal article indexed for PubMed is assigned a unique numerical identifier that is called the PubMed Identifier or PMID for short. For example, PMID 23033231 corresponds to this article .
Creating PubMed searchesEdit
Main article: Creating PubMed searches.