@article{01295506,
title = {Periodic solutions for a third order differential equation under conditions on the potential.},
journal = {Portugaliae Mathematica. Nova S\'erie},
volume = {55},
year = {1998},
pages = {475-484},
zbl = {0923.34045},
language = {en},
url = {http://dml.mathdoc.fr/item/01295506}
}
Minhós, Feliz. Periodic solutions for a third order differential equation under conditions on the potential.. Portugaliae Mathematica. Nova Série, Tome 55 (1998) pp. 475-484. http://gdmltest.u-ga.fr/item/01295506/