@article{05897639, title = {Existence and uniqueness of periodic solution for nonlinear second-order ordinary differential equations.}, journal = {Boundary Value Problems [electronic only]}, volume = {2011}, year = {2011}, doi = {10.1155/2011/192156}, zbl = {1219.34058}, language = {en}, url = {http://dml.mathdoc.fr/item/05897639} }
Zu, Jian. Existence and uniqueness of periodic solution for nonlinear second-order ordinary differential equations.. Boundary Value Problems [electronic only], Tome 2011 (2011) . doi : 10.1155/2011/192156. http://gdmltest.u-ga.fr/item/05897639/