The first resource focuses specifically on tools for finding journal articles and other types of material in classical studies. The resources which follow them are more general in scope.
JSTOR is a collection of scholarly ebooks and journals across disciplines. The journal archive includes back issues and some current issues.
If you search a database and the full article's not there, don't despair. Look for the "FindIt" button: or FindIt@BC. Find It will offer help including: