Google Scholar - Google Scholar is a freely accessible web search engine that indexes the full text of scholarly...
Scinapse - Scinapse is a free, nonprofit, Academic search engine for papers, serviced by Pluto Network.
SemanticScholar - An academic search engine that utilizes artificial intelligence methods to provide highly relevant results and novel tools to filter them with ease.
Biohunter - Biohunter is a one-stop portal for literature search, batch-download PDFs and reference manager
ResearchGate - Access scientific knowledge, and make your research visible
Mendeley - Easily organize your papers, read & annotate your PDFs, collaborate in private or open groups, and securely access your research from everywhere.