@article{05237105,
title = {Periodic solutions of second-order nonautonomous dynamical systems.},
journal = {Boundary Value Problems [electronic only]},
volume = {2006},
year = {2006},
doi = {10.1155/BVP/2006/25104},
zbl = {1140.34366},
language = {en},
url = {http://dml.mathdoc.fr/item/05237105}
}
Schechter, Martin. Periodic solutions of second-order nonautonomous dynamical systems.. Boundary Value Problems [electronic only], Tome 2006 (2006) . doi : 10.1155/BVP/2006/25104. http://gdmltest.u-ga.fr/item/05237105/