ZHANG, K. Nontrivial solutions of fourth-order singular boundary value problems with sign-changing nonlinear terms. Topological Methods in Nonlinear Analysis, [S. l.], v. 40, n. 1, p. 53–70, 2012. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2012.022. Acesso em: 22 jul. 2024.