DINH, N. V.; CHI, T. K. Van der Pol systems with various restoring elements. Vietnam Journal of Mechanics, Hanoi, Vietnam, v. 28, n. 2, p. 67–73, 2006. DOI: 10.15625/0866-7136/28/2/5521. Disponível em: https://vjs.ac.vn/index.php/vjmech/article/view/5521. Acesso em: 25 apr. 2024.