In addition to providing electronic access to an increasing number of full-text books and articles, library catalogs, databases, and indexes also provide access to the vast amount of information that is still available only in print.
Keep in mind that despite its apparent size, the Web still holds only a fraction of the world's published information. The overwhelming majority is still held in libraries and archives around the world.
Library catalogs, databases, and indexes are the best tools to use to find scholarly books and journal articles.