Patent Information
Mechanical Engineering

U.S. Patent & Trademark Office Databases
The latest patents issued (1976-present) are full text and images and can be searched with keywords among other ways (name, patent number, classification).  Earlier patents (1790-1975) are images and thus can only be searched by patent number and current US classifications. 

U.S. Patent & Trademark Office 
Provides access to all USPTO tools.  Consider searching the Index to the U.S. Patent Classification, the Manual of Classification, and the Classification Definitions.  Together, they will provide you with a good understanding of how patents are organized.

European and World Patents
Patents from over 71 countries are provided by the European Patent Office.  Patents are searchable in a variety of ways.  Coverage for many countries go back as far as 1920; some even earlier.  Many provide full text and images.  Over 38 Million patent documents.

Canadian Patents Database
Over 1,400,000 patents of Canadian origin.  Searchable text and images back to 1920.

Patent Fetcher
If you need a complete patent in a single pdf file, this system might be for you.  However, it is limited to only US utility, design, and plant patents; and it is only searchable by patent number.