@article{IVM_1967_6_a7,
     author = {J. P. Konovalov and S. N. Shimanov},
     title = {Periodic solutions of quasi-harmonic systems with retardation},
     journal = {Izvesti\^a vys\v{s}ih u\v{c}ebnyh zavedenij. Matematika},
     pages = {59--67},
     year = {1967},
     number = {6},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/IVM_1967_6_a7/}
}