%0 Journal Article
%T QUADRATIC SYSTEMS POSSESSING A WEAK FOCUS OF ORDER TWO AND A SINGULAR POINT WITH A ZERO CHARACTERISTIC ROOT<br>
%J 科学通报(英文版)
%D 1990
%I 
%K quadratic system
%K weak focus
%K limit cycle<br>
%U http://www.alljournals.cn/get_abstract_url.aspx?pcid=01BA20E8BA813E1908F3698710BBFEFEE816345F465FEBA5&cid=96E6E851B5104576C2DD9FC1FBCB69EF&jid=DD6615BC9D2CFCE0B6F945E8D5314523&aid=8DD575CF89FA966317D1AB02F6FCB908&yid=8D39DA2CB9F38FD0&vid=6209D9E8050195F5&iid=B31275AF3241DB2D&sid=3389C664025A98F9&eid=3389C664025A98F9&journal_id=1001-6538&journal_name=科学通报(英文版)&referenced_num=0&reference_num=0