Academic Resource Search. More than a billion sources: encyclopedia, monographies, magazines.

WorldCat - a search for the contents of 20 thousand worldwide libraries. Find out where lies the nearest rare book you need.

Springer Link - access to more than 10 million scientific documents: books, articles, research protocols.

Bioline International is a library of scientific bioscience journals published in developing countries.

RePEc (Research Papers in Economics) - volunteers from 102 countries have collected almost 4 million publications on economics and related science.

Science Gov is an American state search engine on 2200+ scientific sites. More than 200 million articles are indexed.

PDF Drive is the largest website for free download of books in PDF format. Claiming over 225 million names.

Base search is one of the most powerful researches on academic studies texts. More than 100 million scientific documents, 70% of them are free