var lastScrollY=0;//滚动条距顶部位置
function heartBeat(){ 
    var diffY;
    if (document.documentElement && document.documentElement.scrollTop)
         diffY = document.documentElement.scrollTop;
    else if (document.documentElement)
         diffY = document.documentElement.scrollTop
    else
         {/*Netscape stuff*/}
    
    percent=.1*(diffY-lastScrollY); 
    if(percent>0)percent=Math.ceil(percent); 
    else percent=Math.floor(percent); 
try{
    document.getElementById("gvLeftAd").style.top=parseInt(document.getElementById("gvLeftAd").style.top)+percent+"px";
}catch(ex){}
try{
    document.getElementById("gvRightAd").style.top=parseInt(document.getElementById("gvRightAd").style.top)+percent+"px";
}catch(ex)
{

}
    lastScrollY=lastScrollY+percent; 
}

window.setInterval("heartBeat()",100);//每0.1秒钟执行一次