@article{EJDE_2006__2006__a194,
     author = {Li,  Zhixiang and Wang,  Xiao},
     title = {Existence of positive periodic solutions for neutral functional differential equations},
     journal = {Electronic journal of differential equations},
     year = {2006},
     volume = {2006},
     zbl = {1099.34063},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/EJDE_2006__2006__a194/}
}