5Carol Tenopir.Virtual Reference Service in a Real Wrold [J].Library Journal,2001,(12):38.
6Jeffrey T.Penka.The Technological Challenges of Digital Reference.D-Lib Magazine,February 2003,http://www.dllb.ors／dlib／february03／penka／02penka.html.
7Carol Tenopir. Virtual Reference Service in a Real World. Library Journal,2001;(12)
