Italian Language and Literature
Your best place to start is JHU's Italian Language + Literature Databases. Particularly useful for literary research in Italian are:
Find scholarly articles easily. It's not everything out there, but it's a lot.
Set your Scholar Preferences for JHU, to be connected to online articles.
These are good collections to cross search.
Books on D-level
The main Italian Language and Literature collections are found on D-level at MSEL under the following call numbers:
PG (Compact shelving): Books on Italian language and literature, cataloged before 7/96.
PC 1001-1977 (Blue Label Section): Books on Italian language cataloged after 7/96.
PQ 4001-5999 (Blue Label Section): Books on Italian literature cataloged after 7/96.