@article{AUPO_2006__45_1_a11,
     author = {Lig\k{e}za, Jan},
     title = {On the existence of one-signed periodic solutions of some differential equations of second order},
     journal = {Acta Universitatis Palackianae Olomucensis. Facultas Rerum Naturalium. Mathematica},
     pages = {119--134},
     publisher = {mathdoc},
     volume = {45},
     number = {1},
     year = {2006},
     mrnumber = {2321304},
     zbl = {05184554},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/AUPO_2006__45_1_a11/}
}