HU, Shouchuan; PAPAGEORGIOU, Nikolaos S. Nontrivial solutions for superquadratic nonautonomous periodic systems. Topological Methods in Nonlinear Analysis, [S. l.], v. 34, n. 2, p. 327–338, 2009. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2009.045. Acesso em: 8 jul. 2025.