file_get_contents 输出乱码问题

<?php 
header("Content-Type:text/html;charset=utf-8"); 
$keyworld="跟班网"; 
$keyworld=iconv("utf-8","gb2312",$keyworld); 
$url = "http://www.baidu.com/s?f=8&wd=$keyworld"; 
$html = file_get_contents($url); 
$html = iconv("gb2312", "utf-8//IGNORE",$html); 
echo $html;
?>