Some examples regarding Shodan's keywords

[Geography]
country:US
city:Guangzhou
geo:33.5,36.3

[Time]
before:01/01/2014
after:01/01/2014

[Network and System Scan]
net:216.0.0.0/16
port:443
os:"windows 2003"

[Site and Page Scan]
hostname:google.com
title:"Server Room"

[Exclusion]
-port:80