@article{DAN_1984_277_6_a8,
     author = {A. P. Makhmudov},
     title = {Nonlinear perturbations of regular spectral problems with a},
     journal = {Doklady Akademii Nauk},
     pages = {1318--1323},
     publisher = {mathdoc},
     volume = {277},
     number = {6},
     year = {1984},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1984_277_6_a8/}
}