Invariant Tori of Duffing-Type Equations

In this paper we prove the existence of invariant tori and thus the boundedness of all solutions and the existence of quasiperiodic solutions for a class of Duffing-type equations wherepj(t) (j=0, 1, ..., n) are 1-periodicC(1)functions and wherepj(t) (j=n+1, ..., 2n) are 1-periodicC(2)functions.