$str="http://www.baidu.com/s?wd=js%E8%8E%B7%E5%8F%96php%E5%8F%98%E9%87%8F&tn=ichuner_1_dg&ie=utf-8";
preg_match("/(?:baidu.+?wd=|baidu.+?kw=|baidu.+?word=|soso.+?w=|sogou.+?query=|bing.+?q=|114.+?kw=)([^&]*)/i",$str,$matches);
$keystr=urldecode($matches[1]);

            $str="http://www.baidu.com/s?wd=js%E8%8E%B7%E5%8F%96php%E5%8F%98%E9%87%8F&tn=ichuner_1_dg&ie=utf-8";
            var re = /(?:baidu.+?wd=|baidu.+?kw=|baidu.+?word=|soso.+?w=|sogou.+?query=|bing.+?q=|114.+?kw=)([^&]*)/i
            alert($str.match(re)[1])

------解决方案--------------------

JScript code

<script>
var str = "http://www.baidu.com/s?wd=js%E8%8E%B7%E5%8F%96php%E5%8F%98%E9%87%8F&tn=ichuner_1_dg&ie=utf-8";
var matches = str.match(/(?:baidu.+?wd=|baidu.+?kw=|baidu.+?word=|soso.+?w=|sogou.+?query=|bing.+?q=|114.+?kw=)([^&]*)/i);
var keystr = decodeURI(matches[1]);
alert(keystr)
</script>