RT Journal T1 Periodic Solutions for a Singular Liénard Equation with Sign-Changing Weight Functions A1 Shiping Lu,Shile Zhou,Xingchen Yu PB Acta mathematica scientia,Series A FD 2021-06-01 YR 2021 JF Acta mathematica scientia, Series A JO Acta mathematica scientia,Series A VO 41 IS 3 SP 686 DO K1 ;Periodic solution;Singularity;Continuation theorem;Coincidence degree principle LK {http://121.43.60.238/sxwlxbA/EN/article/article_16419.shtml}