按设定的时间打开一个后台的窗口
<!-- http://www.knowsky.com -->
<!-- bbs http://bbs.knowsky.com-->
<!--把如下代码加入到<head>中区域中-->
注意:刷新几次你就可以看到效果了!
<script LANGUAGE="JavaScript">
bg = new Array(2);
bg[0] = 'http://www.knowsky.com/images/logo.gif'
bg[1] = '.gif'
bg[2] = 'http://www.knowsky.com/images/12090.gif'
index = Math.floor(Math.random() * bg.length);
document.write("<BODY BACKGROUND="+bg[index]+">");
</script>