Espacenet offers free access to 70 million+ patent documents worldwide. Includes information about inventions and technical developments from 1836 to today.
Patent full-page images back to 1790. Searchable in five-year blocks back to 1976, and in one additional block covering the years 1790-1975. The 1790-1975 block contains only patent numbers and current US Classifications (in addition to links to full-page images). Patents prior to 1976 can be searched for only by patent number or current US classification.