US Patent & Trademark OfficeThe search engine is easy-to-use, but full documentation may not be available. So you might search the USPTO Patent database to get the patent number, and then get the full-text in Lexis-Nexis.
Lexis Nexis Academic Universe
Patents @ Lexis-NexisSelect as many sources as you wish. “Combined U.S. patents,” “European patents,” Japan Patent Abstracts”, and/or “Patent Cooperation Treaty patent applications” are likely to be your best choices.