IMANBAEV, N.; SADYBEKOV, M. On spectral properties of a periodic problem with an integral perturbation of the boundary condition. Eurasian Mathematical Journal, [S. l.], v. 4, n. 3, p. 53–62, 2013. Disponível em: https://emj.enu.kz/index.php/main/article/view/536. Acesso em: 30 sep. 2025.