中文摘要：

从产品纵向差异的角度出发，假设双寡头垄断市场中，一个企业在生产方面依赖于另一个企业，研究了双寡头企业的短期市场行为和长期市场行为：一是从短期的角度出发，将产品质量视为外生变量，研究了双寡头企业的产量策略和利润状况，并对均衡结果做了比较静态分析，研究结果表明，两个企业都有提高或降低各自产品质量的动机，取决于双方现有的产品质量水平；二是从长期的角度出发，将产品质量视为内生变量，研究了双寡头企业的质量与产量决策，研究结果表明，存在唯一的产品质量均衡，均衡质量没有表现出较大的差异化，而是表现出较小的差异化．此外，无论从短期的角度还是从长期的角度来看，都不存在高质量优势，相反，存在低质量优势．

英文摘要：

Supposing that an enterprise depends on another enterprise in production in a duopolistic market, the short-term and long-term market behaviors of the two enterprises are studied in the paper from the perspective of vertical products differentiation. From the short-term perspective, the paper assumes product quality to be an exogenous variable and examines the output strategy and profit conditions of duopolistic enterprises. Moreover, a comparative static analysis of the equilibrium results is made in the paper. The findings indicate that both enterprises have motives to increase or decrease their respective product quality, which depends on their present level of product quality. From the long-term perspective, with product quality assmumed as an endogenous variable, the paper analyzes the quality and output strategies of duopolistic enterprises. We proved that there exists a sole equilibrium in product quality of the duopolistic enterprises and high differentiation doesn＇ t appear, and there is just a slight difference in the quality of two kinds of products. In addition, there is no high-quality advantage either in the short-term or long-term market behaviors. In contrast, there exists a low- quality advantage.