How can I find just the books that I can download in Google Books?
While there is no way to restrict search results to downloadable books only, you can limit your results to books that are fully viewable by using the Advanced Search feature of Google Books. Just select the "Full view only" option, enter your search terms and click "Google Search." Although not all books that are fully viewable are also downloadable as PDF files, this will help narrow your search results closer to books that are downloadable.
You might be interested in out Google Books LibGuide or eBooks Libguide, see links below: