@article{DE_1969_5_11_a3, author = {I. A. Pasynkova}, title = {The existence of families of periodic solutions of a system of $n$ second order differential equations in the resonance case}, journal = {Differencialʹnye uravneni\^a}, pages = {1984--1989}, publisher = {mathdoc}, volume = {5}, number = {11}, year = {1969}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/DE_1969_5_11_a3/} }