<?php
$str2='<title>我是标题</title>  (<(<(ccc';
$a=preg_replace("!<title>(.*?)</title>!is","\\1",$str2);
echo $a;
?>

<?php
$str2='<title>我是标题</title>  (<(<(ccc';
preg_match("!<title>(.*)</title>!isU",$str2,$a);
echo $a[1];
?>