After each search, click on the DETAILS tab to find out.
You type deep vein thrombosis and PubMed translates it into the following searches:
Venous Thrombosis (MeSH – subject heading search)
venous and thrombosis (searches for the words, but not necessarily together or in that order)
“venous thrombosis” (searches for the phrase)
deep and vein and thrombosis (searches for the words, but not necessarily together or in that order)
“deep vein thrombosis” (search for the phrase)
Checking Details after each search allows you to keep track of the searches PubMed carries out on your behalf.
More information from PubMed or see the Information & Library Skills section on Moodle for lots of support material on searching PubMed.