Existence Results for Periodic Solutions of Nonautonomous Second-Order Differential Systems with $(q, p)$-Laplacian. Communications in Mathematical Research, [S. l.], v. 28, n. 3, p. 281–288, 2021. Disponível em: https://www.global-sci.com/index.php/cmr/article/view/8741. Acesso em: 27 feb. 2026.