@article{Maciejewski:2004,
  author  = "A. Maciejewski and M. Przybylska",
  title   = "Darboux polynomials and first integrals of natural polynomial Hamiltonian systems",
  journal = "Physics Letters A",
  number  = "no 326",
  pages   = "219--226",
  year    = "2004",
}