GooMedic has a good post on how to search for medical books. Not only the search method is explained but the’re suggestions for specific search engines, not only google books but several search engines I was not aware of. Some examples:
eBookee . which is a books portal with a medical section , it provide a download links for the medical books on free file hosting services .
Medicalndx.com is an old medical service which considered an old school medical search engine , where you can seach for news , medical events , treatment , diganosis , …. along with medical books search .
Well done, thanks GooMedic