00531naa#a2200169#i#450# EN\\bibl\2819 20241227085754.5 2308-8877 20140616b2014####ek#y0engy0150####ca RUS RU Free van der pol equation Journal article Voronezh FSBE Institution of Higher Education Voronezh State University of Forestry and Technologies named after G.F. Morozov 2014 2 с. Journal article local Zuev S. Vasil'evich zh-szf.ru