@article{EJDE_2015__2015__a75,
     author = {Guan,  Wen and Wang,  Da-Bin},
     title = {Existence of infinitely many periodic solutions for second-order nonautonomous {Hamiltonian} systems},
     journal = {Electronic journal of differential equations},
     year = {2015},
     volume = {2015},
     zbl = {1318.34058},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/EJDE_2015__2015__a75/}
}