[1] Algaba A, Garcia C, Reyes M. Characterization of a monodromic singular point of a planar vector field[J]. Nonlinear Analysis, 2011, 74(3/4): 54025414.
[2] 陈兰荪, 王明淑. 二次系统极限环的相对位置与个数[J]. 数学学报, 1979, 22(6): 751758.
[3] 张芷芬, 丁同仁, 黄文灶, 等. 微分方程定性理论[M]. 北京: 科学出版社, 1985.
[4] Dumortier F, Llibre J, Artes J. Qualitative Theory of Planar Differential Systems[M]. Berlin: Springer, 2006.
[5] Berezovskaya F S, Medvedeva N B. The asymptotics of he return map of a singular point with fixed Newton diagram[J]. Journal of Mathematical Sciences, 1991, 60(6): 17651781.
[6] Dumortier F. Singularities of vector fields in the plane[J]. J Differ Equ, 1977, 23: 53106.
[7] Algaba A, Freire E, Gamero E, et al. Monodromy, centerfocus and integrability problems for quasihomogeneous polynomial systems[J]. Nonlinear Analysis, 2010, 72(3/4): 17261736.
[8] Algaba A, Freire E, Garcia C. Center of quasihomogeneous polynomial planar systems[J]. Nonlinear Analysis: Real World Applications, 2012, 13: 419431.
[9] Sansone G, Conti R. Nonlinear Differential Equations[M]. New York: Pergamon Press, 1964.