8[10]Li Ks, Xu KM, Peiris Js, et al. Characterization of H9 Subtype influenza viruses from the ducks of southern China: a candidate for the aext influenze pandemic in humans[ J ]. J virol,2003,12: 6988 - 6994.
5Y. K. Choi,S. M. Goyal,H. S. Joo. Prevalence of swine influenza virus subtypes on swine farms in the United States[J] 2002,Archives of Virology(6):1209～1220
