中国科学院数学与系统科学研究院期刊网
ON THE EXISTENCE OF PERIODIC SOLUTIONS FOR LIENARD SYSTEMS
丁伟岳
ON THE EXISTENCE OF PERIODIC SOLUTIONS FOR LIENARD SYSTEMS
WEIYUE  DING 
数学学报 . 1982, (5): 626 -632 .  DOI: 10.12386/A1982sxxb0061