BASE: The Bielefeld Academic Search Engine (BASE) contains 4,000 sources and provides search results from over 100 million documents. It also offers an advanced search option that allows users to narrow their research.
Refseek: Refseek is a web search tool for students and researchers. You can access over a billion documents, books, newspapers, and journals without getting distracted by ads or sponsored links.
Google Scholar: connects you with hundreds of relevant scholarly journals. What’s more, it provides formatted citations in MLA, AP, or APA that you can export to RefWorks or BibTex.