$(document).ready(
        function() {
            $("#CodeImg").attr({ src: "yanzhengma.aspx", alt: "验证码" });
            $("#CodeImg").click( 
            function () 
            { 
                $("#CodeImg").attr("src",chgUrl('yanzhengma.aspx'));  
            }
            );
            
        });
        
function clear_login()
{
    document.getElementById("txtName").value="";
    document.getElementById("txtPwd").value="";
}
function chgUrl(url)
{   
    var timestamp = (new Date()).valueOf();          
    url = url + "?timestamp=" + timestamp;      
    return url;  
}