中国科学院数学与系统科学研究院期刊网
The Three-parameter Unifoldings of Several Kinds of Planar Polycycles with Two Saddle-nodes and One Saddle
LiQin Zhao
Acta Mathematica Sinica, Chinese Series . 1998, (2):  .  DOI: 10.12386/A1998sxxb0068