求教高手解一个积分，小女子拜求：）

[angel4296]

a=9.8427;
b=3.1491;
y= (a*b)^((a+b)/2)*x^((a+b)/2-1)*besseli(a-b,2*(a*b*x)^0.5)*(2/pi^0.5)*exp(-t^2);
Y1=int(int(y,t,500/707*x,inf),x,0,inf)

得到的解为
Warning: Explicit integral could not be found.
> In sym.int at 58

Y1 =

int(1621193981275812845703240236051/590295810358705651712*x^(54959/10000)*besseli(8367/1250,1/140737488355328*2455728123682660124221610393600^(1/2)*x^(1/2))*(-pi^(1/2)*erf(500/707*x)+pi^(1/2)),x = 0 .. Inf)

哪位高手能知道怎么得到Y1的近似解？？谢谢了：）