00501naa#a2200169#i#450# EN\\bibl\12242 20250115065955.3 1992-5980 20160621b2016####ek#y0engy0150####ca RUS RU Solving eigenvalues problems for Helmholtz equation by point-source method Journal article rostov on don Don state technical University 2016 8 с. Journal article local Shcherbakova Elena naukaru.ru