1. Morozov AD, Shil’nikov LP. On nonconservative periodic systems similar to two-dimensional Hamiltonian ones. Pricl. Mat. i Mekh. (Russian). 1983;47(3):385-394
2. Morozov AD. Quasi-conservative systems: Cycles, resonances and chaos. World Scientific Series on Nonlinear Science Series A. 1998;30. http://www.worldscientific.com/worldscibooks/10.1142/3238
3. Morozov AD. Resonances and chaos in parametric systems. Journal of Applied Mathematics and Mechanics. 1994;58(3):413-423
4. Melnikov VK. On stability of a center under periodic in time perturbations. Work of the Moscow Mathematical Society. 1963;12:3-52
5. Andronov AA, Leontovich EA, Gordon II, Maiyer AG. The Theory of Bifurcations of Dynamical Systems in a Plane. Moscow, Russia: Publ. Nauka; 1967