5Darst, B.C. Development of the potash fertilizer industry [ J ]. Fertilizer Research, 1991, 28:103 - 107.
6Velk, P.L.G. The role of fertilizers in sustaining agriculture in SubSaharan Africa[ J ]. Fertilizer Research, 1990, 26 : 327- 339.
7He, H., Jie Zhou, Yongjao Wu, et al. Modeling the response of surface water quality to the urbanization in Xi' an, China[J]. Journal of Environmental Management. 2008, 86 : 731 - 749.
8He, H., Jie Zhou, Yongiao Wu, et al. Estimating water quality pollution impacts based on economic loss models in urbanization process in Xi ' an, China [ J ]. Journal of Urban Planning and Development, 2007,133 ( 3 ) : 151 - 160.
9David, R Hakes. The Study Guide for Principles of Economics[M].Beijing: China Machine Press, 2004.