为啥使用file_get_contents获取不到百度竞价内容

为什么使用file_get_contents获取不到百度竞价内容
$url = 'http://www.baidu.com/s?wd=%E4%BF%9D%E5%81%A5%E5%93%81&rsv_spt=1&issp=1&f=8&rsv_bp=0&rsv_idx=2&ie=utf-8&tn=baiduhome_pg&rsv_enter=0&inputT=2625&rsv_pq=f8ac4a3700000dd9&rsv_t=54ffCzY5xNXYlNcEjuJTNfBzIrJob0iUn2whzhsN7JtTaA6R0Z7yxIGlNFSR5t0vyOID&rsv_sug3=5&rsv_sug1=4&rsv_sug2=0&rsv_sug4=4274';
$info=file_get_contents($url);
echo $info;
?>


我想获取百度竞价排名前三的几个站，使用file_get_contents输出了百度搜索结果页的内容但是为什么竞价内容不显示啊？

原来是这个的有竞价位的

但是我输出的就没有了竞价内容了请问下各位高手是什么原因啊？





------解决思路----------------------

	$url = 'http://www.baidu.com/s?rsv_bp=0&rsv_spt=3&ie=utf-8&rsv_sug3=23&rsv_sug4=267&rsv_sug1=22&rsv_sug2=0&inputT=18&wd=%E4%BF%9D%E5%81%A5%E5%93%81&tn=89040009_1_pg';
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_USERAGENT, 'Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/31.0.1650.63 Safari/537.36');
    curl_setopt($ch, CURLOPT_URL, $url);
    curl_setopt($ch, CURLOPT_HEADER, 0);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    $content = curl_exec($ch);
    curl_close($ch);

	echo $content;

大概检查了下，百度验证了user-agent，如果为空就没有竞价那一块
------解决思路----------------------

header('Content-type: text/html;charset=utf-8');
$url = 'http://www.baidu.com/s?wd=%E4%BF%9D%E5%81%A5%E5%93%81&rsv_spt=1&issp=1&f=8&rsv_bp=0&rsv_idx=2&ie=utf-8&tn=baiduhome_pg&rsv_enter=0&inputT=2625&rsv_pq=f8ac4a3700000dd9&rsv_t=54ffCzY5xNXYlNcEjuJTNfBzIrJob0iUn2whzhsN7JtTaA6R0Z7yxIGlNFSR5t0vyOID&rsv_sug3=5&rsv_sug1=4&rsv_sug2=0&rsv_sug4=4274';  

$opts = array( 
  'http'=>array( 
    'user_agent' => $_SERVER['HTTP_USER_AGENT']
  ) 
); 
$context = stream_context_create($opts);

$info=file_get_contents($url, false, $context);
echo $info;