United States Patent & Trademark Office (USPTO)
USPTO consists of information about all US patents (including utility, design, reissue, plant pattents and SIR documents) from the first patent issued in 1790 to the most recent issue week. Patents from 1976 to the present offer full seachable text.
Also use Patent Lens for patents created in Europe and Australia as well as the US. The PDF format of patents cannot easily be printed or downloaded from the USPTO database. We recommend you do most of your searching in Patent Lens.
Link to resource:
United States Patent & Trademark Office (USPTO)