@article{EJDE_2014__2014__a53,
     author = {Liao,  Fang-Fang},
     title = {Periodic orbits with small angular momentum for singular radially symmetric systems},
     journal = {Electronic journal of differential equations},
     year = {2014},
     volume = {2014},
     zbl = {1305.34061},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/EJDE_2014__2014__a53/}
}