@article{EJDE_2013__2013__a194,
     author = {Gu,  Hua and An,  Tianqing},
     title = {Existence of infinitely many periodic solutions for second-order {Hamiltonian} systems},
     journal = {Electronic journal of differential equations},
     year = {2013},
     volume = {2013},
     zbl = {1293.34055},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/EJDE_2013__2013__a194/}
}