Regarding Kevin McElhone's query [180116 MMDigest -- Every U.S.
patent is on the US Patent Office website http://uspto.gov/  and will,
I assume, be so indefinitely.  This will always be the definite source.
The "full image" search option may require leading zeros to create an
8-digit number, and a PDF viewer to see the results:
http://patft.uspto.gov/netahtml/PTO/patimg.htm 

The European patent organisation runs a wonderful search tool,
Espacenet, which accesses almost everything European, American, and
more:  https://worldwide.espacenet.com/ 

Secondary search engines may be a tiny bit more user-friendly,
but may change from time to time.  It's always good to know where the
definitive sources are.

The growth in availability of patent data online over recent years has
been astounding.

Julian Dyer