Patent Offices
German Patent and Trademark Office
http://dpma.de/
European Patent Office
http://www.european-patent-office.org
World Intellectual Property Organization
http://www.wipo.int
Office for Harmonization in the Internal Market
http://www.oami.eu.int
U.S. Patent Office
http://www.uspto.gov
Japanese Patent Office
http://www.jpo.go.jp
Research possibilies
DEPATISNET
https://depatisnet.dpma.de/
DPINFO (registration required)
https://dpinfo.dpma.de/index.html
DPMApublikationen
https://publikationen.dpma.de/start.do
Espacenet
http://preview.espacenet.com/home?CY=ep&LG=de
Epoline
http://register.epoline.org/espacenet/ep/de/srch-reg.htm
International Patent Classification (IPC)
http://depatisnet.dpma.de/ipc/index.html