function autoSel()
{
    if(getScrollTop()=="0")
    {
        document.getElementById("full").style.display="none";
    }
    else
    {
        document.getElementById("full").style.display="block";
    }
    //document.getElementById("type").options[id].selected=true;
}
lastScrollY=0;
function heartBeat(){ 
var diffY;
if (document.documentElement && document.documentElement.scrollTop)
    diffY = document.documentElement.scrollTop;
else if (document.body)
    diffY = document.body.scrollTop
else
    {/*Netscape stuff*/}

percent=.1*(diffY-lastScrollY); 
if(percent>0)percent=Math.ceil(percent); 
else percent=Math.floor(percent); 
document.getElementById("full").style.top=parseInt(document.getElementById("full").style.top)+percent+"px";

lastScrollY=lastScrollY+percent; 
}
suspendcode="<div id=\"full\" style='right:2px;POSITION:absolute;TOP:500px;z-index:100; display:none;'><a href='#' onclick='javascript:scroll(0,0)'><img src='images/top.png' border=0 alt='返回顶部'></a></div>"

document.write(suspendcode);
window.setInterval("heartBeat()",1);
window.onscroll=autoSel;


function getScrollTop()
{   
    var scrollTop=0;   
    if(document.documentElement&&document.documentElement.scrollTop)   
    {   
        scrollTop=document.documentElement.scrollTop;   
    }   
    else if(document.body)   
    {   
        scrollTop=document.body.scrollTop;   
    }   
    return scrollTop;   
}