In a world dominated by Google, there are still many excellent researchers who are experts in various fields of science and other intelligent information that you can use. Below is a list of really useful sites that most have never heard of.
www.refseek.com — search for academic resources. Over a billion sources: encyclopedias, monographs, journals.
www.worldcat.org — content search engine from 20,000 world libraries. Find out where the nearest rare book you need is.
www.link.springer.com — access to over 10 million scientific documents: books, articles, research protocols.
www.bioline.org.br — A library of biological journals published in developing countries.
www.repec.org — Volunteers from 102 countries have collected nearly 4 million publications in the field of economics and related sciences.
www.science.gov — is an American state-owned company. Search engine for over 2,200 scientific websites. Over 200 million articles are indexed.
www.pdfdrive.com – A free site for downloading PDF books. Collect over 225 million names.
www.base-search.net – one of the most powerful search engines for academic texts. Over 100 million scientific documents, 70% of which are free.