While searching the database for your required books by author, title or subject.
Ebrary offers an increasing selection of more than 20,000 e-books in business, economics, computers, engineering, and technology.
Free Online Books: Listing more than 35,000 English works in various formats.
Textbooks in the Open Textbook Library are considered open because they are free to use and distribute, and are licensed to be freely adapted or changed with proper attribution.
OAPEN promotes and supports the transition to open access for academic books by providing open infrastructure services to stakeholders in scholarly communication.
While searching database for your required books by author, title or subject, use keywords i.e.Math, Calculus, Geography, Electrical Engineering,Physics, Calculus etc.