Here's a list of sites Christopher Seymore collected that we find very useful!
www.refseek.com – Academic Resource Search. More than a billion sources: encyclopedias, monographies, magazines.
www.worldcat.org – Search for the contents of 20 thousand worldwide libraries. Find out the nearest rare book you need.
https://link.springer.com - access to more than 10 million scientific documents: books, articles, research protocols.
www.bioline.org.br – Library of scientific bioscience journals published in developing countries.
http://repec.org – Almost 4 million publications on economics and related sciences.
www.science.gov – American state search engine on 2200+ scientific sites. More than 200 million articles indexed.
www.base-search.net – Powerful research on academic studies texts. More than 100 million scientific documents, 70% of them free
https://www.ecosia.org/ – Tech company that plants and protects trees. With 100% of its profits to the planet, Ecosia has planted over 214,229,374 trees since December 2009
Yandex.com – Technology company that builds intelligent products and services powered by machine learning to help consumers and businesses better navigate the online and offline world.
Gutenberg.org – Library of over 75,000 free eBooks
Duckduckgo.com – Search and browse with this browser for more protection. Doesn’t track you.
Presearch.io – Community-powered, decentralized search engine. Gives better results while protecting your privacy and rewarding you when you search.
Ebscohost.com – Reliable information for all kinds of research
Startpage.com – Global privacy technology company that puts privacy first. Protects their personal data online.