Periodic Solutions of a Class of Duffing Differential Equations. Journal of Nonlinear Modeling and Analysis, [S. l.], v. 1, n. 2, p. 167–177, 2024. DOI: 10.12150/jnma.2019.167. Disponível em: https://global-sci.com/index.php/jnma/article/view/13514. Acesso em: 6 dec. 2025.