someone posted this on facebook… its awesome! i just looked up studies on one of the sites about negative symptoms of sz. it bought up 800 articles! can’t wait to read 
"Google is so powerful that it “hides” other search systems from us. We just don’t know the existence of most of them.
Meanwhile, there are still a huge number of excellent searchers in the world who specialize in books, science, other smart information.
Keep a list of sites you never heard of.
[www.refseek.com] - Academic Resource Search. More than a billion sources: encyclopedia, monographies, magazines.
[www.worldcat.org] - a search for the contents of 20 thousand worldwide libraries. Find out where lies 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]is a library of scientific bioscience journals published in developing countries.
[http://repec.org] - volunteers from 102 countries have collected almost 4 million publications on economics and related science.
[www.science.gov] is an American state search engine on 2200+ scientific sites. More than 200 million articles are indexed.
[www.base-search.net] is one of the most powerful researches on academic studies texts. More than 100 million scientific documents, 70% of them are free "