1. Perturbation Methods;NAYFEH,1973
2. Nonlinear Oscillations;NAYFEH,1979
3. Introduction to Perturbation Techniques;NAYFEH,1981
4. Introduction to Non-linear Mechanics;KRYLOV,1943
5. Asymptotic Methods in the Theory of Nonlinear Oscillations;BOGOLIOUBOV,1961