As with journals, there are several databases applicable to art history. Most will index many different sources of information, and cover a wide range of periods, artist, themes, etc. The easiest way to access a particular database for a given subject is the following:
Each database includes a brief description, so you don't find yourself searching for Rubens in a database devoted to 20th century conceptual art, for example. Although space precludes a full list of relevant databases, some of the most popular include: