| This thesis is devoted to study the structure and existence of nonoscillatory solutions with respect tothe fourth order nonlinear di?erential equations of the form:(?)whereαandβare both positive constants, and p(t) is also continuous and positive functions on an interval[t0,∞)(t0≥0)and q(t) is too. The paper chie?y establishes su?cient conditions and necessary conditions ofexistence of the positive solutions for the equation under the cases thatα>β> 0 andβ>α> 0. |
