1. Bogoliubov, N. N. and Mitropolski, Y. A., Asymptotic Methods in the Theory of Nonlinear Oscillations, Gordon and Breach Science Publishers, New York, 1961 (in Russian-4th edition Nauka, Moskva, 1974).
2. Hayashi, Ch., Nonlinear Oscillations in Physical Systems, Princeton University Press, Princeton, NJ 1985.
3. Nayfeh, A. H. and Mook, D. T., Nonlinear Oscillations, Wiley-Interscience, New York, 1979.
4. Kriukov, B. J., Forced Oscillations in Strongly Nonlinear Systems, Masinostroienie, Moskva, 1984 (in Russian).
5. Szemplińska-Stupnicka, W., The Behavior of Non-Linear Vibrating Systems, Kluwer Academic Publishers, 1990.