@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/