1. Free and forced oscillations of a class of mechanical system;Kane;Int. J. non-linear Mech.,1966
2. Introduction to Non-Linear Mechanics;Kryloff,1949
3. Uber eine neue Methode zur Losung gewisser Variationsprobleme der Mathematische Physik;Ritz;J. f. reine u. angew. Math.,1908
4. Free vibration of a rectangular plate with damping considered;Stanišić;Q. Appl. Math.,1955
5. Asymptotic Methods in the Theory of Non-linear Oscillations;Bogoliuboff,1961