PERESTYUK, N. A.; TKACH, A. B. Periodic solutions of a weakly nonlinear system of partial differential equations with pulse influence. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 49, n. 4, p. 601–605, 1997. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5038. Acesso em: 5 dec. 2025.