Patent Searching
Espacenet - European Patent Office
Search titles of over 50 million patents from 71 countries. Full text PDF of US utility patents 1836-Present. Also see Espacenet Classification Search and Espacenet Online Tutorials
WIPO (world intellectual property organisation). The PATENTSCOPE database 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.
US Patent Search
https://www.uspto.gov/patents-application-process/search-patents
USPTO Inventor Assistance Center
https://www.uspto.gov/patents-application-process/search-patents
Google Patent Search
Google Advanced Patent Search
https://www.google.com/advanced_patent_search