1. Periodic Solutions of Singular Lagrangian Systems;Ambrosetti,1993
2. Continuation theorems for periodic perturbations of autonomous systems;Capietto;Trans. Amer. Math. Soc.,1992
3. T-periodic solutions for a second order system with singular nonlinearity;del Pino;Differential Integral Equations,1995
4. Periodic solutions for a conservative system of differential equations with a singularity of repulsive type;Fonda;Nonlinear Anal.,1995
5. Periodic Solutions of Scalar Second Order Differential Equations with a Singularity;Fonda,1993