Specialization, Diversification, and Environmental Technology Life Cycle
分析了区域相关多样化和不相关多样化对绿色技术发展的影响，并考察了这种影响在技术生命周期不同阶段的变化。研究发现，不相关多样化在早期阶段是主要驱动力，而相关多样化在技术成熟期更为重要。
The article analyzes whether and to what extent regional related and unrelated variety matter for the development of green technology, and whether their influence differs over the technology life cycle. Using patent and socioeconomic data on a thirty-year (1980–2009) panel of US states, we find that unrelated variety is a positive predictor of green innovative activities. When unpacked over the life cycle, unrelated variety is the main driver of green technology development in the early stages, while related variety becomes more prominent as the technology enters into maturity.