DAO, N. V. Some problems on nonlinear oscillations. Vietnam Journal of Mechanics, Hanoi, Vietnam, v. 29, n. 3, p. 187–195, 2007. DOI: 10.15625/0866-7136/29/3/5531. Disponível em: https://vjs.ac.vn/index.php/vjmech/article/view/5531. Acesso em: 20 may. 2024.