@article{GDZPPN002490617,
title = {On Existence of Positive Periodic Solutions.},
journal = {Monatshefte f\"ur Mathematik},
volume = {125},
year = {1998},
pages = {343-350},
zbl = {0899.34028},
url = {http://dml.mathdoc.fr/item/GDZPPN002490617}
}
Wójcik, Klaudiusz. On Existence of Positive Periodic Solutions.. Monatshefte für Mathematik, Tome 125 (1998) pp. 343-350. http://gdmltest.u-ga.fr/item/GDZPPN002490617/