1. "Catalog" tab to the Duke Libraries catalog
Here are some subject examples of what you can find:
2. 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.
Art Discovery Group https://artdiscovery.net/ - the "art" segment of a Worldcat search. Easy, direct, free for anyone to use. Map the holdings listed back to Duke. Searching directly can be done through https://artlibraries.on.worldcat.org/discovery
Arcade - The collections of the Frick Art Reference Library, the Brooklyn Museum Library and The Museum of Modern Art Library.
https://archive.org/details/metmuseumlibraries - All the digitized images from the Metropolitan Museum of Art's library (via the Internet Archive). Handy when you only want pdf full text.