There are many variables to determining if something is covered by copyright protection. It's safe to assume that anything published recently - even if it's just posted on the web - has some level of copyright protection and you cannot copy it and use it for your own purposes unless you either have permission from the author or publisher, or can justify your use as a Fair Use (used for noncommercial purposes, for your own private research, or used in non-profit education. Fair Use is complex and limited.

This is a handy chart for reviewing copyright terms:
http://www.unc.edu/~unclng/public-d.htm

This is similar, a bit more complicated and thorough:
http://copyright.cornell.edu/resources/publicdomain.cfm

Fair Use: http://www.loc.gov/teachers/usingprimarysources/copyright.html