The U.S. Patent & Trademark Office (USPTO) Patent Database includes full text of patents from 1790 - present and also provides TIFF images of most of them.
By Patent Number
Go to USPTO Database.
Select Patent Number Search or Publication Number Search.
Go to USPTO Database and select Quick Search. Enter keywords in the search box.
Find a patent that is close to what you're looking for.
Note the Cooperative Patent Classification (CPC) number/Subclass for that patent, e.g. A01D 711/111 .
Do a search of that Class/Subclass in USPTO Database to find more patents on that subject.
Go to CPC Classification System Scheme and search for common terms or keywords.
Alternately, you can use the WIPO Catchword list for ideas.
Use the Class/Subclass numbers you found to check the CPC Classification System Scheme to see if they are on target.
Search by Class/Subclass numbers in USPTO Database.
You can use the same method of searching in other patent databases on the web. See the Patent Websites in this guide for more databases.
-Above text by Dave Schmitt, University of California San Diego Library
US Patent and Trademark Office Pages
From Other Sources
To find Tesla's Patents:
Go to the US Patent office website and type "tesla motors inc" into the search field. You don't even have to type the whole thing; it will pop up the correct search term once you get "tesla". Instant list of all Tesla patents.