Hello,

There are various sites available using which you can download relevant information of your subjects in BSc.

Though the portion totally depends on the University in which you are studying but for reference purposes you can use sites such as -

www.pdfdrive.com (//www.pdfdrive.com)

www.archive.org (//www.archive.org)

Hope this helps you or else you can type the name of the particular book and see whether certified sites are providing e-books or not.