DINH, Nguyen Van; CHI, Tran Kim. Van der Pol systems with various restoring elements. <b>Vietnam Journal of Mechanics</b>, Hanoi, Vietnam, v. 28, n. 2, p. 67–73, 2006. DOI: 10.15625/0866-7136/28/2/5521. Disponível em: https://vjmech.vast.vn/vjmech/article/view/5521. Acesso em: 9 nov. 2025.