建立了联系R3中一类二次系统与二维流形球面S~2的切向量场之间的桥梁,证明了R~3中一类二次系统存在5个极限环,而且这5个极限环分别位于该系统的5个不变闭锥上.
The authors find a bridge between a class of vector fields in R3 and the tangent vector fields of two-dimensional manifold S~2,and prove the existence of at least 5 limit cycles for a class of quadratic system in R3,which are located on the five invariant closed cones of the system respectively.