//截取摘要
public static function mbsubstr($str){
    $strleng = mb_strlen($str,"utf8");
    $mbstr = mb_substr($str,0,140,‘utf8‘);
    $strdstr = mb_substr($str,140,$strleng,‘utf8‘);
    $strlengs = mb_strlen($strdstr,‘utf8‘);
    $strc = "";
    for($i=0;$i<$strlengs;$i++){
        $strn = mb_substr($strdstr,$i,1,‘utf8‘);
        if($strn == "。" || $strn == "？" || $strn == "！"){
            break;
        }
        $strc .= $strn;
    }
    $strd = $mbstr.$strc;
    //echo $strleng."@".mb_strlen($strd,‘utf8‘)."@".$strd."<br>";
    return $strd;
}

php 截取代码方法（140个字后的。）