asp:ScriptManager ID="ScriptManager1" runat="server">
/asp:ScriptManager> //必须有且一定在updatepanel前面
asp:UpdatePanel ID="UpdatePanel1" runat="server">
ContentTemplate>
　　% =DateTime.Now.ToString()%>
/ContentTemplate>
Triggers>
　　asp:PostBackTrigger ControlID="btn" />
　　asp:AsyncPostBackTrigger ControlID="btn2" EventName="click" />
/Triggers>
/asp:UpdatePanel>

asp:Button runat="server" Text="刷新1" id="btn"/>
asp:Button runat="server" Text="刷新2" id="btn2" />
% =DateTime.Now.ToString()%>