Google Books is an electronic index of digitized books and e-books that is separate from Google Scholar. There is not a one-size-fits-all model for what is available on Google Books. There are different levels of access and that depends upon each book in the collection. These levels are:
Preview and snippet view both are great alternatives to buying a book if you only need a particular section of the book. In addition, you can Interlibrary Loan a book and use Google Books to supplement your research needs until the book comes into the Library. If you're interested, read about Google Books on Google's official site.