Collection of scientific works in 12 volumes. Mathematics and Nonlinear Mechanics in 4 volumes vol.3. Asymptotic methods in the theory of nonlinear oscillations / Sobranie nauchnykh trudov v 12-ti tomakh. Matematika i nelineynaya mekhanika v 4 t. T.3. Asimptoticheskie metody v teorii nelineynykh kolebaniy