Lens
lens.org
A free and open scholarly and patent search engine covering 227 million patent records and 209 million scholarly works — with full-text search, citation analysis, and export to reference managers.
Why it is useful
The only place to search both academic literature and patent databases together for free. Patent searches are invaluable for understanding what's been filed in a technology area before building something. The scholarly coverage is comparable to Scopus and Web of Science but completely free. Citation metrics and reference exports are included at no cost, making it a practical replacement for expensive academic database subscriptions.