var nowheight=0;    //初始广告层高度 
var maxheight=60;    //广告层最大高度 
var adobj; 
var openL; 
var closL; 
var addfunc; 
var handobj; 
var reducefunc;         
var speed=7;        //层卷动速度 
function showtopad() { 
    adobj=document.getElementById("bigad"); 
    openL=document.getElementById("openL"); 
    closL=document.getElementById("closL"); 
    if (nowheight<=0) { 
        openL.style.display="none"; 
        adobj.style.display="block"; 
        addfunc=setInterval("addheight()",1); 
    } 
} 
function closetopad() { 
    if (nowheight>0) { 
        callreduceheight(); 
        if (typeof(handobj)=="number") { 
            clearTimeout(handobj); 
        } 
    } 
} 
function addheight() { 
    nowheight+=speed; 
    if (nowheight>maxheight) {  
        clearInterval(addfunc); 
        closL.style.top=maxheight-30; 
        closL.style.display="block"; 
        handobj=setTimeout("callreduceheight()",6000);//显示广告时间 
        return; 
    } 
    adobj.style.height=nowheight+"px"; 
} 
function callreduceheight() { 
    closL.style.display="none"; 
    reducefunc=setInterval("reduceheight()",1); 
} 
function reduceheight() { 
    adobj.style.height=nowheight+"px"; 
    nowheight-=speed; 
    if (nowheight<=0) { 
        clearInterval(reducefunc); 
        adobj.style.display="none"; 
        openL.style.display="block"; 
        return; 
    } 
}