Free patent Databases

Indian Patent Office Database search website

https://ipindiaservices.gov.in/publicsearch

Patentscope Database

The Patentscope database of World Intellectual Property Organization provides access to international Patent Cooperation Treaty (PCT) applications in full text format on the day of publication, as well as to patent documents of participating national and regional patent offices.

https://www.wipo.int/patentscope/en/

European Patent Office

http://ep.espacenet.com/

US Patent and Trademark Office

http://patft.uspto.gov/