TOPOLOGICAL STRUCTURE OF INTEGRAL CURVES OF THE DIFFERENTIAL EQUATION (dy)/(dx)=(ax~3+bx~2y+cxy~2+dy~3)/(a_1x_3+b_1x~2y+c_1xy~2+d_1y~3)

• 微分方程(dy)/(dx)=(ax~3+bx~2y+cxy~2+dy~3)/(a_1x~3+b_1x~2y+c_1xy~2+d_1y~3)的积分曲线的拓扑结构