TIAN, Y.; GE, W. Multiple positive solutions for periodic boundary value problem via variational methods. Tamkang Journal of Mathematics, [S. l.], v. 39, n. 2, p. 111–120, 2008. DOI: 10.5556/j.tkjm.39.2008.21. Disponível em: https://journals.math.tku.edu.tw/index.php/TKJM/article/view/21. Acesso em: 1 may. 2024.