Patent Explorer Derwent's searchable site of U.S. and European patents. Patent Knowledge Center Derwent's searchable site of U.S. and European patents. Patent Search System STO's Internet Patent Search System. Provides keyword searchable classification index, international patent information retrieval, patent news service, and links to commercial services. QPAT-US Search all U.S. patents issued since 1974.
Abstracts are free, but require registration.
This free IBM site features an intuitive interface and offers access to patent documents from the U.S., Europe and Japan, plus patent applications from the World Intellectual Property Office. U.S. Patent and Trademark Office Comprehensive site offering free fulltext patents and trademarks in a searchable database, plus general information and links to other web sites.