@article{PORMA_1989__46_S_115830,
     author = {Kastenholz, Michael and Lange, Horst and Nieder, Dirk},
     title = {Periodic solutions of nonlinear {Schr\"odinger} equations},
     journal = {Portugaliae mathematica},
     pages = {517--537},
     publisher = {mathdoc},
     volume = {46},
     number = {S},
     year = {1989},
     mrnumber = {1080771},
     zbl = {0723.35074},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PORMA_1989__46_S_115830/}
}