3Hahan W. Stability of Motion [M]. Berlin-New York: Springer-Verlag, 1957.
4Yoshizawa T. Stability Theory by Liapunov's Second Method[M]. Takyo:The Math Soc of Japan, 1995.
5Hale J K. Ordinary Differential Equations [M]. 2nd ed. New York: Willey-Interscience, 1980.
6Buica A, Gasull A, Yang J. The third order Melnikov function of a quadratic center under quadratic perturbations [J]. J Math Anal Appl, 2007,331 (1):443-454.
7Champneys A, Lord G, Computation of homoclinic solutions to periodic orbits in a reduced-water-wave problem[J]. Physica D: Nonlinear Phenomena, 1997,102 ( 1/2 ): 101-124.
8Chow S N, Hale J K, Mallet-Paret J. An example of bifurcation to homoclinic orbits [J]. J Differential Equations, 1980,37 ( 3 ): 351-371.
9Dumortier F, LI Cheng-zhi, ZHANG Zhi-fen. Unfolding of a quadratic integrable system with two centers and two unbounded heteroclinic loops [J]. J Differential Equations, 1997,139 (1): 146-193.
10LI Cheng-zhi, Rousseau C. A system with three limit cycles appearing in a Hopf bifurcation and dying in a homoclinic bifurcation: the cusp of order 4 [J]. J Differential Equations, 1989,79( 1 ): 132-167.
