原理是利用JS判断访问设备的类型，进而跳转，代码如下：

    <html>
    <head>
    </head>
    <body >
    <script type="text/javascript">
    function getCookie(c) {
        var b;
        return (b = document.cookie.match(RegExp("(^| )" + c + "\x3d([^;]*)(;|$)"))) ? unescape(b[2]) : ""
    }
     
    var browse_edition = getCookie("browse_edition");
    if ("web" != browse_edition) {
        var ua = navigator.userAgent.toLowerCase();
        if (/iphone|ipod|android|windows phone|blackberry/.test(ua)) {
                        this.location = 'http://m.baidu.com';
                }
    }
    </script>
    </html>