@article{BASM_2017_2_a8,
     author = {Iurie Calin and Stanislav Ciubotaru},
     title = {The {Lyapunov} quantities and the center conditions for a~class of bidimensional polynomial systems of differential equations with nonlinearities of the fourth degree},
     journal = {Buletinul Academiei de \c{S}tiin\c{t}e a Republicii Moldova. Matematica},
     pages = {112--130},
     publisher = {mathdoc},
     number = {2},
     year = {2017},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/BASM_2017_2_a8/}
}