6Thorstoen Joachims,et al.web watcher:Atour guide for the www.http://www.cs,cmu.edu.
7H C M de Kroon,et al. Improving learning accuracy in information filtering.http://www.cs.cmu.edu.
8Chu heting, Rosenthal M. Search engines for the world wide web: A comparactive study and evaluation methodology [J]. In: Proceedings of the 59th Annual Meetings of the American Society for Information Science, Baltimor, MD, 1996, October21-24, 127- 135.
9Franic Z. How to use and cite Internet resources,with special attention to radiation protection and health physics WWW sites [J]. Arb Hig Rada Toksikol,1997, 48 (3): 323-334.
10Stone VL, Fishman DL, Frese DB. Searching online and Web - based resources for information on natural products used as drugs [J]. Bull Med Libr Assoc,1998, 86 (4): 523-527.
