@article{EJDE_2001__2001__a3,
     author = {Cheng, Sui Sun and Zhang, Guang},
     title = {Existence of positive periodic solutions for non-autonomous functional differential equations},
     journal = {Electronic Journal of Differential Equations},
     publisher = {mathdoc},
     volume = {2001},
     year = {2001},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/EJDE_2001__2001__a3/}
}