PHP curl 在浏览器中获得 404 一切都很好

http://www.rlsnet.ru/tn_alf_letter_DF.htm - 我有这个网址，在浏览器中它工作正常，但是如果我使用它提出请求：

$url = 'http://www.rlsnet.ru/tn_alf_letter_DF.htm';
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
$data = curl_exec($ch);
print_r(curl_getinfo($ch));
exit;

我得到这个结果：

Array ( [url] => http://www.rlsnet.ru/tn_alf_letter_DF.htm [content_type] => text/html; charset=windows-1251 [http_code] => 404 [header_size] => 214 [request_size] => 72 [filetime] => -1 [ssl_verify_result] => 0 [redirect_count] => 0 [total_time] => 14.925294 [namelookup_time] => 5.401249 [connect_time] => 5.643545 [pretransfer_time] => 5.643608 [size_upload] => 0 [size_download] => 87314 [speed_download] => 5850 [speed_upload] => 0 [download_content_length] => -1 [upload_content_length] => 0 [starttransfer_time] => 12.941717 [redirect_time] => 0 )

http_code是404，为什么会这样？

更新：

$url = 'http://www.rlsnet.ru/tn_alf_letter_DF.htm';
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
curl_setopt($ch, CURLOPT_USERAGENT, 'Mozilla/5.0 (Windows NT 6.2; WOW64; rv:17.0) Gecko/20100101 Firefox/17.0');
curl_setopt($ch, CURLOPT_HEADER, TRUE);
curl_setopt($ch, CURLOPT_REFERER, 'http://www.rlsnet.ru');
$data = curl_exec($ch);
print_r(curl_getinfo($ch));
exit;

仍然得到 404