中文摘要：

城市流描述了城市的基本活动部分，体现了城市的对外服务功能。城市流强度揭示了城市对外联系的强弱，它与城市中心性的极强相关性表明，城市流强度是表征城市对外服务功能的量化指标。通过中国13个主要城市群的城市流强度与结构分析，从城市流视角探讨中国城市群对外服务功能空间分布特征及其增长情况。研究表明，长三角、珠三角城市群是全国性的以制造业为主的综合型对外生产服务中心，京津冀北城市群是全国性的以第三产业为主的综合型对外生产服务中心，山东半岛城市群初步形成以第二产业为主的全国性对外生产服务中心，成渝、辽中南等其余9个城市群为区域性对外生产服务中心。研究指出，城市群往往生成于我国各级产业轴线交汇的地方，由产业轴级别差异，将会形成不同规模等级的城市群，由此可以从各级产业轴线上寻找和培育新的城市群。研究认为，由城市流强度占GDP比重而确定的外部贡献率，是城市的基本活动部门对地区生产总值增长的贡献纷顽，城市群区域内部密切的经济联系与交流提高了各城市的外部贡献率，由城市间密切经济联系而形成的城市流是城市群演化发育的内在机制之一。

英文摘要：

Urban flows describes the basic activities of city, reflects the urban external services, and reveals the contacts between cites. And correlation between urban flows intensity and urban centrality shows that urban flows intensity is the quantitative index of urban external service functions. With the case study of 13 major urban agglomerations in China, this article analyses their urban flows intensity and structures, and discusses spatial distribution and growth situation of external services function in terms of urban flows. Research shows that the Yangtze River Delta, the Pearl River Delta, Beijing-Tianjing and Northern Hebei agglomerations have the most mighty external production services, which constitute the three major Chinese integrated production bases in service. Shandong peninsula, the middle-south part of Liaoning province agglomerations are the fourth and fifth production service bases in China, while the agglomerations in Midwest China has weaker external services functions. The Yangtze River Delta, Pearl River Delta agglomerations as national comprehensive external production service centers specialize in manufacturing. Beijing-Tianjing and Northern Hebei agglomerations specialize in the tertiary industry, while Shandong peninsula agglomerations form a national external production service centre mainly in the secondary industry.