Welcome!  This guide is an overview of the database PubMed.

As you can see, there are several tabs that mention other associated databases. If you are wondering which database to use.  

Here is a snapshot:

PubMed:  Citation only database.  5200 journal titles.  Excellent place to search when you want to do a literature review.

PubMed Central: Full text database. 3000 journal titles.  So a much smaller collection than PubMed.  This has articles from the late 1700s to the present. All articles are discoverable by either searching in PubMed Central or PubMed. Great place to search when you want immediate access to an article but don't have access to 

Medline Ultimate: 1,650 active full-text, non-open access journals.  The PG Library subscribes to this database.  The interface with Medline Ultimate is easier to use than PubMed or PubMed Central's interfaces.