【摘要】 本文研究具有正负系数的中立型微分方程，分别得到了这类方程存在和不存在正解的充分条件，并建立了不存在正解的比较定理．更多还原

【Abstract】 In this paper we consider the neutral differential equations with positive andnegative coefficients.Sufficient conditions for the existence and nonexistence of positivesolutions are obtained respectively.Some comparison theorems also have been established.更多还原