"If you haven't already seen it, here is a visual featuring what we believe are some of the best academic search engines for teachers and research students ..."
https://scholar.google.com/ https://www.eric.ed.gov http://www.virtuallrc.com/ http://www.citeulike.org/ http://jurn.org/#gsc.tab=0 https://academic.microsoft.com/home https://www.loc.gov/ https://www.refseek.com/ https://www.sciencedirect.com/ https://www.academia.edu/Via Leona Ungerer