求助下面文章（英文的最好能已经有中文版）

    生产者服务业发展与制造业效率提升

    Audretsch, D. B. and Feldman, M.(1996). R&D Spillovers and the Geography of Innovation and Production. American Economic Review, 86(3): 630-40

    Howells, J.(2002). Tacit Knowledge, Innovation and Economic Geography. Urban Studies, 39(3): 871-84