1. "Catalog" tab to the Duke Libraries catalog
Here are some subject examples of what you can find:
2. Kubikat (again!) Book & article catalog of four German art-history libraries, covering all languages and with an English interface) Kunsthistorisches Institut (Florence) Zentralinstitut für Kunstgeschichte (Munich). Deutsches Forum für Kunstgeschichte (Paris) and the Bibliotheca Hertziana (Rome).
3. Google Books & Google Scholar
Google Books allows you to search books by key-word. It does not display the whole book. Use LIBX.
Google Scholar is the same but for articles.
Worldcat - combined catalog of all libraries
Use Worldcat to locate exhibition catalogs and books for interlibrary loan and archives of collections. There's a "libraries with this item" link that shows NC libraries first.