var speed = 30 
butong_net_top2.innerHTML = butong_net_top1.innerHTML   //克隆butong_net_top1为butong_net_top2 

function Marquee1()
{ 
    //当滚动至butong_net_top1与butong_net_top2交界时 
    if(butong_net_top2.offsetTop - butong_net_top.scrollTop <= 0)
    {   
        butong_net_top.scrollTop -= butong_net_top1.offsetHeight    //butong_net_top跳到最顶端 
    }
    else
    { 
        butong_net_top.scrollTop++;
    } 
}
 
var MyMar1=setInterval(Marquee1,speed)  //设置定时器
 
//鼠标移上时清除定时器达到滚动停止的目的 
butong_net_top.onmouseover=function() {clearInterval(MyMar1)} 

//鼠标移开时重设定时器 
butong_net_top.onmouseout=function(){MyMar1=setInterval(Marquee1,speed)}