为何我单值绑定不行，代码如下，请指教

<HTML>
<HEAD>
<title>WebForm1</title>
<meta name="GENERATOR" Content="Microsoft Visual Studio .NET 7.1">
<meta name="CODE_LANGUAGE" Content="C#">
<meta name="vs_defaultClientScript" content="JavaScript">
<meta name="vs_targetSchema" content="http://schemas.microsoft.com/intellisense/ie5">
<script language=javascript>
<!--
var str =<%=str%>
alert(1);
//-->
</script>
</HEAD>
<body MS_POSITIONING="GridLayout">
<form id="Form1" method="post" runat="server">
<FONT face="宋体">
<table align =center id =tble>
<tr>
<td><%#str%></td>
</tr>
</table>
</FONT>
</form>
</body>
</HTML>