MeSH is a great resource,a the­saurus, espe­cially sig­nif­i­cant if you access Med­line – from what­ever source.  (PubMed is the free ver­sion, acces­si­ble every­where any­one has access to the internet.)

MeSH means Med­ical Sub­ject Headings.  They are assigned by index­ers at the National Library of Med­i­cine.  This the­saurus is com­plete with def­i­n­i­tions or scope notes.  It is orga­nized in a hier­ar­chi­cal fash­ion so that if you wanted to search all antibi­otics, for exam­ple, you wouldn’t have to sep­a­rately type all of them, but could just “explode” the main heading.  You can limit the head­ings to a major con­cept, the most impor­tant concept(s) in the arti­cle.  You can also attach sub­head­ings, such as adverse effects of antibi­otics.