@article { author = {}, title = {PERIODIC SOLUTIONS OF CERTAIN THREE DIMENSIONAL AUTONOMOUS SYSTEMS}, journal = {Journal of Sciences, Islamic Republic of Iran}, volume = {10}, number = {2}, pages = {-}, year = {1999}, publisher = {University of Tehran}, issn = {1016-1104}, eissn = {2345-6914}, doi = {}, abstract = {There has been extensive work on the existence of periodic solutions for nonlinear second order autonomous differantial equations, but little work regarding the third order problems. The popular Poincare-Bendixon theorem applies well to the former but not the latter (see [2] and [3]). We give a necessary condition for the existence of periodic solutions for the third order autonomous systems, This may become useful in further investigations. Our claims are proved and supported by certain examples.}, keywords = {}, url = {https://jsciences.ut.ac.ir/article_31492.html}, eprint = {https://jsciences.ut.ac.ir/article_31492_4c876434368592fefa4f89f39e5bc3b9.pdf} }