BARTSCH, T.; WANG, Z.-Q. Sign changing solutions of nonlinear Schrödinger equations. Topological Methods in Nonlinear Analysis, [S. l.], v. 13, n. 2, p. 191–198, 1999. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.1999.010. Acesso em: 20 jan. 2022.