//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;
}