DINH, N. V. On a variant of the asymptotic procedure (II: Weakly nonlinear non-autonomous systems). Vietnam Journal of Mechanics, Hanoi, Vietnam, v. 26, n. 2, p. 76–82, 2004. DOI: 10.15625/0866-7136/26/2/5691. Disponível em: https://vjs.ac.vn/index.php/vjmech/article/view/5691. Acesso em: 7 dec. 2021.