offer some useful web sites about mechanical engineering.?

Answer 1

http://www.me.utexas.edu/~me302/classnotes/ME-intro_files/frame.htm

There are so many areas of mechanical engineering. For example one useful piece of turbomachinery: http://www.gepower.com/prod_serv/products/turboexpanders/en/index.htm

Answer 2

You can always check out the American Society of Mechanical Engineers:
http://www.asme.org/
Or if your interested in Automotive Engineering, check out:
www.sae.org