Medline Reference database for all areas of biomedicine, with more than 21 million citations from 1946. Issued by: National Library of Medicine, USA
EMBASE Reference database with more than 23 million biomedical and pharmacological citations from 1974, including Medline from 1966. Issued by: Elsevier
The Cochrane Library Database on evidence-based medicine: includes full text of systematic reviews, protocols and register of clinical studies. Issued by: Cochrane Collaboration
PubMed More than 29 million citations for biomedical literature. Contains MEDLINE (since 1966, with MeSH) and OLDMEDLINE (1949 to 1965, without MeSH)