U.S. Patent & Trademarks Office (USPTO)
The U.S. Patents from 1790 to the most current submissions are available on the from the USPTO website in full-text. See The 7-Step U.S. Patent Search Strategy for a structured approach to searching the USPTO.
Google provides a google interface to explore the USPTO patent database.
This is a database that offers international coverage, though they note that it is not comprehensive. Information about 81national patent offices is available from this site at Global Patent Data Coverage, July 2011.
A search tool for patents world-wide that searches the European Patent Office’s DocDB bibliographic data from 1907 to present, EP Grants from 1980 to present; U.S. Patent Applications from 2001, Grants from 1976 to present; and WIPO PCT Applications from 1978 to present.
SciFinder Scholar, a database developed and maintained by the American Chemical Society's Chemical Abstracts Service, see http://www.cas.org/content/references/patentcoveragecovers patents from nine patent offices worldwide
In addition, the country patents and years covered by SciFinder can be seen at http://www.cas.org/content/references/patyear.
Utility patents are granted for any new and useful process, machine, article of manufacture or composition of matter or any new and useful improvement thereof. Utility patents confer protection for 20 years from the date of application.
Design patents are granted for any new, original and ornamental design for an article of manufacture. Design patents are granted for a term of 14 years.
Plant patents are granted for the discovery or invention and asexual reproduction of any new, distinct variety of plant. Plant patents are granted for a term of 20 years.