User registration, a subscription fee, or some other type of fee may be required to access the full-text of articles in some journals. This permits publishers easily to link from references in their published articles directly to entries in PubMed. PubMed also provides access and links to the integrated molecular biology databases included in NCBI's Entrez retrieval system. These databases contain DNA and protein sequences, 3-D protein structure data, population study data sets, and assemblies of complete genomes in an integrated system. The file contains over 11 million citations dating back to the mid-1960's.
Coverage is worldwide, but most records are from English-language sources or have English abstracts.
See Journal LinkOut Providers for a list of web-based journals to which PubMed currently provides links. Publishers and other data providers are responsible for providing NLM with the links for each article through LinkOut, therefore the list of journals may change frequently. User registration, a subscription fee, or some other type of fee may be required to access the full text of articles for some journals. Policies vary by provider and by journal. Contact the journal publishers as noted on their individual web sites for specific access information.