I've just been checking some of the links in that link I gave - and some of them no longer exist.
There is a much shorter list of search sites at
http://www.makeuseof....e-deep-invisible-web/ however one site they list (Intute) is now no longer being updated as a result of funding cuts, but the existing database will still be available for another couple of years. They also have tutorials aimed at teaching uni students how to do academic research in various disciplines, so they might be worth looking at.