var time = 500;
var h = 0;
function addCount(){
if(time>0){time--;h = h+5;}
else{return;}
if(h>250){return;} //高度
document.getElementById("ads").style.display = "";
document.getElementById("ads").style.height = h+"px";
setTimeout("addCount()",30);
} 

window.onload = function showAds(){
addCount();
setTimeout("noneAds()",20000); //停留时间自己适当调整
}
var T = 260;
var N = 250; //高度
function noneAds(){
if(T>0){T--;N = N-5;}else{return;}
if(N<0){document.getElementById("ads").style.display = "none";return;}
document.getElementById("ads").style.height = N+"px";
setTimeout("noneAds()",30); 
}