根据UserAgent判断，如果是移动端则访问mobile文件夹。

<system.webServer>
        <rewrite>
            <rules>
                <rule name="UserAgentRedirect" stopProcessing="true">
                    <match url="^(.*)$" />
                    <conditions>
                        <add input="{HTTP_USER_AGENT}" pattern="((AppleWebKit.*Mobile.*)|Android|Linux|iPhone|iPad|MicroMessenger|micromessenger|(\sQQ)|(Windows\ Phone)|MQQBrowser)" />
                    </conditions>
                    <action type="Rewrite" url="/mobile/{R:1}" />
                </rule>
            </rules>
        </rewrite>

    </system.webServer>