Google Scholar - Google Scholar is a freely accessible web search engine that indexes the full text of scholarly...
Web of Knowledge - Thomson Reuters Web of KnowledgeSM is a research platform that gives you access to objective...
Google Custom Search - Google Custom Search enables you to create a search engine for your website, your blog, or a collection of websites.
ResearchGate - Access scientific knowledge, and make your research visible
Scopus - Scopus is a bibliographic database containing abstracts and citations for academic journal articles.
Synthical - AI-powered collaborative research environment. You can use it to get recommendations of articles based on reading history, simplify papers, find out what articles are trending, search articles by meaning (not just keywords), and so on.