@article{GDZPPN002216280, title = {Time Periodic Solutions of Nonlinear Wave Equations.}, journal = {Manuscripta mathematica}, volume = {4}, year = {1971}, pages = {165-194}, zbl = {0219.35062}, url = {http://dml.mathdoc.fr/item/GDZPPN002216280} }
Rabinowitz, Paul H. Time Periodic Solutions of Nonlinear Wave Equations.. Manuscripta mathematica, Tome 4 (1971) pp. 165-194. http://gdmltest.u-ga.fr/item/GDZPPN002216280/