@article{MZ_1963__82_170182,
     author = {Hans-Wilhelm Knobloch},
     title = {Eine neue {Methode} zur {Approximation} periodischer {L\"osungen} nicht-linearer {Differentialgleichungen} zweiter {Ordnung.}},
     journal = {Mathematische Zeitschrift},
     pages = {177--197},
     publisher = {mathdoc},
     volume = {82},
     year = {1963},
     zbl = {0117.05404},
     url = {http://geodesic.mathdoc.fr/item/MZ_1963__82_170182/}
}