Google Books is an excellent source for finding the full text book, especially those printed before 1922. Books published before this date are in the public domain and often available online. You can also find more current books online via Google Books but they are likely incomplete or only include limited previews.

You can search by title if you know the book you need. You can also search by keyword.

In some cases the whole book or part of the book (preview) is available online. Books with No preview only provide the bibliographic information of the book.

In some cases, Google Books provides snippets. Snippets are only parts of the text where the keywords you searched are highlighted.

Hathi Trust is another source of fully online books, documents, and other resources. Not everything listed in the Hathi Trust catalog is available on but it can be a useful tool for identifying sources. (Note: OSU is not a partner institution so there is no login. Not everything will be available fulltext online)

Internet Archive is a large collection of books, media, newspapers and other sources that have been digitized.

Searching Internet Archive is a little tricky. It's best to keep your search terms broad and use the facets on the right hand side to make your search more specific.