@article{article45888938,
title   = {Phase portraits of quadratic polynomial vector fields having a rational first integral of degree 3},
author = {Llibre, Jaume and Oliveira, Regilene Delazari dos Santos},
year = {2009},
doi = {10.1016/j.na.2008.07.012},
journal   = {Nonlinear Analysis: Theory, Methods & Applications}
}