TY - JOUR AU - A. Ya. Kovalenko TI - Perturbation of the periodic solutions of differential equations in the case when the spectrum of the monodromy operator of the generating equation contains~1 JO - Izvestiâ vysših učebnyh zavedenij. Matematika PY - 1971 SP - 44 EP - 49 IS - 7 PB - mathdoc UR - http://geodesic.mathdoc.fr/item/IVM_1971_7_a5/ LA - ru ID - IVM_1971_7_a5 ER -