8HELPMAN, ELHANAN. International trade in the presence of product differentiation, economies of scale and monopolistic competition, a chamberlin-heckscherohlin approach[J]. Journal of International Economics, 1981,11(3) : 305-340.
9KRUGMAN, PAUL R. Increasing returns, monopolistic competition and international trade[J]. Journal of International Economies, 1979,9(4) :469-179.
10DAVID F, BATTEN, DAVID E, BOYCE. Spatial interaction, transportation, and interregional commodity flow modelsI[J]. Handbook of Regional and Urban Economics, 1987,1(1).