The product called "PubMed" draws information from a couple different places to build it's database.
The following breaks down the differences between MEDLINE, PubMed, and PubMedCentral (PMC).
MEDLINE: the National Library of Medicine's journal citation database. Journals go through rigorous vetting before they are included in MEDLINE. Sources in MEDLINE also have had MeSH subject headings applied to them, and are therefore able to be searched using that controlled vocabulary. Sources in MEDLINE make up a subset of the articles in PubMed and are accessable through PubMed, or through the specialized MEDLINE database (available through the SMCM Library), which offers additional searching and filtering functions.
PubMed: includes everything in MEDLINE, plus works that do not have MeSH subject headings, either because they are pre-prints, or because they were published before 1966, and works deposited in PMC (see below). PubMed also contains records for journal articles that come from MEDLINE accepted journals but are beyond the medical information scope, as well as citations for many books available on the NCBI Bookshelf.
PubMed Central (PMC): contains articles submitted by authors or publishers in compliance with the NIH Public Access Policy and other funding policies that require depositing an Open Access copy of the article in a publicly accessible repository. Though authors and publishers are required to deposit the articles, they still may retain copyright and can impose "embargoes" in which they specify the amount of time that must pass between publication and making the full text freely available (anywhere from six months to a few years).
EndNote citation manager software is available for free to St. Mary's students, faculty, and staff.