9Glander-Hoebel Cornelia, Voigt Kristina, Welzl Gerhard, et al. Comparing search engines with respect to environmental chemistry using statistical and mathematical evaluation methods [J]. Online Information 2001 Proceedings, 2001(4) : 187-195.
10Michael Gordon, Praveen Pathak.Finding information on the World Wide Web:the retrieval eectiveness of search engines [J]. Information Processing and Management, 1999 ( 35 ) :141-180.
