//脚本
<script language="javascript" type="text/javascript">
function callObj(){
var ceng=document.getElementById("filter");
ceng.style.display="block";
ceng.style.width=document.body.clientWidth;
ceng.style.height=document.documentElement.clientHeight;
}
function callDiv(){
var ceng=document.getElementById("filter1");
ceng.style.display="block";
ceng.style.width=document.body.clientWidth;
ceng.style.height=document.documentElement.clientHeight;
}
</script>
//内容
<input type="button" οnclick="callObj()" value="遮住下拉框"/>
<input type="button" οnclick="callDiv()" value="遮不住下拉框"/>
<select id="sel" style="z-index:1">
<option value='aa'>aa</option>
</select>
<div id="filter1" style="position: absolute; top: 0px; filter: alpha(opacity=60); background-color: #777;
z-index: 100; left: 0px; display: none;"></div>
<OBJECT id="filter" style="display:none;z-index: 1000; LEFT: 0px; WIDTH: 152px; POSITION: absolute; TOP: 5px; HEIGHT: 200px" type="text/x-scriptlet" data="about:这是盖住下拉框的东东"></OBJECT>