Periodic Solutions of the Duffing Differential Equation Revisited via the Averaging Theory. Journal of Nonlinear Modeling and Analysis, [S. l.], v. 1, n. 1, p. 11–26, 2024. DOI: 10.12150/jnma.2019.11. Disponível em: https://www.global-sci.com/index.php/jnma/article/view/13505. Acesso em: 5 dec. 2025.