PageHeader : Funkcialaj Ekvacioj, 38 (1995) 519-538 Title : Existence of Periodic Solutions of Second Order Nonlinear Title : Evolution Equations and Applications AuthorInfo : By AuthorInfo : Masaru YAMAGUCHI AuthorInfo : (Tokai University, Japan) section : 1. Introduction section : 2. Proof of Theorem 1.1 section : 3. Two dimensional semilinear wave equations and N-dimensional Klein-Gordon equations section : 4. Some beam equations section : Appendix section : References