In this paper, we study the SchrdingerPoisson system -Δu+V(x) u+λφ(x)u=K(x)f(u),inR3,-Δφ=u2,u>0,inR3, and prove the existence of positive solutions for system (SP) when the nonlinearity f has growth at most linear for λ small, allowing the potential V(x) to vanish at infinity. In addition, also we obtain the nonexistence of a nontrivial positive solution for...