There are a number of different resources you can use to research books on the web. Some allow you to read the full text of a book online for free, while others might provide you with snippets from the book or more information about its contents and publication.

Project Gutenberg — Project Gutenberg is a repository of more than 57,000 texts on a variety of subjects. Most of the books are in the public domain because their copyright has expired; the number of current texts in this repository is relatively small.

Project Gutenberg interface. A list of books including Dracula, The Iliad, and Grimms' Fairy Tales

Google Books — Working in partnership with several libraries, Google has created a huge database of electronic books. Your access to these books will vary: some are available in full, some provide substantial preview views, and some provide only snippet (sentence-length) views. You can find the books in libraries, purchase them, or view the available portions online.

The Google Books searchbox

WorldCat — WorldCat is a database of books and articles held by libraries around the United States and some international libraries. Search WorldCat to find out what's been published in your area and request the items through interlibrary loan.

The OCLC WorldCat searchbox