How to pass value in php page

<script type="text/javascript"> 
function getsel(){
var obj = document.getElementById("sel").value;
if(obj== ""){
obj = "0";
}
    var newhref = "b.php?obj="+obj;
    var ona = document.getElementById(&#39;ona&#39;);
    ona.href = newhref;
}
</script>
<select id="sel">
      <?php foreach ($sql_res as $value) { ?>
<option value="<?php echo $value[belongs];?>"><?php echo $value[belongs];?></option>
 <?php };?>
</select>
<a id=&#39;ona&#39; href="" target="_blank" onclick="getsel()">传值</a>

<?php
$obj = $_REQUEST[&#39;obj&#39;];
echo $obj;
?>