@article{05561928,
title = {Periodic solutions of non-autonomous second order systems with },
journal = {Electronic Journal of Differential Equations (EJDE) [electronic only]},
volume = {2009},
year = {2009},
zbl = {1189.34078},
language = {en},
url = {http://dml.mathdoc.fr/item/05561928}
}
Wang, Zhiyong; Zhang, Jihui. Periodic solutions of non-autonomous second order systems with . Electronic Journal of Differential Equations (EJDE) [electronic only], Tome 2009 (2009) . http://gdmltest.u-ga.fr/item/05561928/