1Holmberg.Guided didactic conversation in distance education[A].Stewart,Keegan, Holmberg, eds. Distance Education: International Perspectives[C]. London: Routledge,1983. 114-22.
2Holmberg.Aspects of Distance Education[J].Comparative Education,1980, 16(2): 107-119.
3Lentell.Promiting interaction: maintaining independence: swallowing the mixture[J]. Open Learning, 1997, 5(2): 24-33.
4Peters. Learning and teaching in distance education[M]. London:Kogan Page,1998.
5Holmberg.On the methods of teaching by correspomdence[M].Lund:Gleerup, 1960.
6Holmberg, Schuemer, Obermeier. Zur Effiziens des gelenkten didak-tischen Gesprdches(with a summary in English) [M]. Hagen:Fern Universitat, 1982.
7Holmberg. Theory and practice of distance education[M].London and New York:Routledge, 1995.
8Popper.The logic of scientific discovery[M].London:Hutchinson,1980.
9Jeong-Im Choi,Michael Hannafin. Situated cognition and learning environments: Roles, structures, and implications for design[J] 1995,Educational Technology Research and Development(2):53~69
10David Lebow. Constructivist values for instructional systems design: Five principles toward a new mindset[J] 1993,Educational Technology Research and Development(3):4~16