中国科学院数学与系统科学研究院期刊网
The Fundamental Group of Open Manifolds with Nonnegative Ricci Curvature
Sen Lin XU, Qin Tao DENG
Acta Mathematica Sinica, Chinese Series . 2006, (2): 353 -356 .  DOI: 10.12386/A2006sxxb0044