ZOU, Y. POSITIVE SOLUTIONS FOR SECOND ORDER INTEGRAL BOUNDARY VALUE PROBLEMS WITH SIGN-CHANGING NONLINEARITIES. Journal of Nonlinear Analysis and Optimization: Theory & Applications (JNAO), [S. l.], v. 4, n. 1, p. 111–117, 2013. Disponível em: https://ph03.tci-thaijo.org/index.php/jnao/article/view/2691. Acesso em: 2 sep. 2026.