ZipSearch searches across many (but not all) of the library's resources, and includes the two major music databases, RILM and Music Index.
Choose "academic journals" to make sure you don't search every recording, score, and mention of, say, Mozart. . .
This is a great place to start to find general information on a topic of interest. It is an encyclopedia. Here you *can* search broadly (i.e. Stravinsky, or Baroque Opera) to: read a scholarly, in depth overview article; get ideas for more specific topics; and to find some good resources from the bibliographies. Remember, you need to actually look at the sources you'll be listing, so you can't just cite a source you see here - you have to track it down!
Since the creation of this database, the New Grove Encyclopedia of Popular Music has also been added to the Grove Music Online product.