@article{GDZPPN002211696,
title = {Periodic solutions of non-autonomous Hamiltonian systems with symmetries.},
journal = {Journal f\"ur die reine und angewandte Mathematik},
volume = {450},
year = {1994},
pages = {149-160},
zbl = {0794.58037},
url = {http://dml.mathdoc.fr/item/GDZPPN002211696}
}
Bartsch, Thomas; Willem, Michel. Periodic solutions of non-autonomous Hamiltonian systems with symmetries.. Journal für die reine und angewandte Mathematik, Tome 450 (1994) pp. 149-160. http://gdmltest.u-ga.fr/item/GDZPPN002211696/