php 分割字符串分词

    public function getKeyWords($title,$i){
    	$keywords_temp = array();
    	while($i>1){
	    	for ($j = 0; $j <  strlen($title) - $i + 1; $j++) {
	            $stemp[] = mb_substr($title, $j,$i,'utf-8');
	        }
	        $i--;
    	}
        return array_filter($stemp);
    }
    $key_arr = getKeyWords('尊重原创，请保证您的文章为原创作品',4);
    print_r($key_arr);