empirical study based on the American universities 知识创新的空间格局:基于美国大学的实证研究:empirical study based on the American universities empirical study based on the equity and efficiency theory General education of American universities an empirical study based on the firms in China an empirical study based on typical cases empirical study based on Shaanxi empirical study based on Chinese warrant and option markets an empirical study based on team learning theory an empirical study based on tone analysis