@article{120254, author = {J\'an Andres and Vladim\'\i r Vl\v cek}, title = {Note to the existence of periodic solutions for higher-order differential equations with nonlinear restoring term and time-variable coefficients}, journal = {Acta Universitatis Palackianae Olomucensis. Facultas Rerum Naturalium. Mathematica}, volume = {30}, year = {1991}, pages = {149-157}, zbl = {0757.34031}, mrnumber = {1166434}, language = {en}, url = {http://dml.mathdoc.fr/item/120254} }
Andres, Ján; Vlček, Vladimír. Note to the existence of periodic solutions for higher-order differential equations with nonlinear restoring term and time-variable coefficients. Acta Universitatis Palackianae Olomucensis. Facultas Rerum Naturalium. Mathematica, Tome 30 (1991) pp. 149-157. http://gdmltest.u-ga.fr/item/120254/
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