9Scherer F M. Firm size, market structure, opportunity, and the output of patented inventions [ J ]. The American Economic Review, 1965, 55(5) : 1097 - 1125.
10Tihanyi L, Richard J A, Hoskisson E R, et al. Institutional ownership differences and international diversification: the effects of boards of directors and technological opportunity [J]. Academy of Management Journal, 2003,46(2) : 195 - 211.