var nowheight=0;    //初始广告层高度
var maxheight=300;    //广告层最大高度         
var speed=7;        //层卷动速度
function showtopad() {
    adobj=document.getElementById("bigad");
    if (nowheight<=0) {
        adobj.style.display="block";
        addfunc=setInterval("addheight()",1);
    }
}
function addheight() {
    nowheight+=speed;
    if (nowheight>maxheight) {  
        clearInterval(addfunc);
        handobj=setTimeout("callreduceheight()",5000);
        return;
    }
    adobj.style.height=nowheight+"px";
}
function callreduceheight() {
    reducefunc=setInterval("reduceheight()",1);
}
function reduceheight() {
    adobj.style.height=nowheight+"px";
    nowheight-=speed;
    if (nowheight<=80) {
        clearInterval(reducefunc);
       // adobj.style.display="none";
		document.getElementById("bigad").innerHTML='<a href=http://www.zhaoshang-sh.com/zhuanti/12year target=_blank/><img src=http://cf.zhaoshang-sh.com/index/12zhounian980-80.gif border=0></a>'
        return;
    }
	
}