function logincheck()
{
	if(trim(document.login_form.username.value)=="")
	{
		alert("请输入用户名!");
		document.login_form.username.focus();
		return false
	}
	if(trim(document.login_form.password.value)=="")
	{
		alert("请输入密码!");
		document.login_form.password.focus();
		return false
	}
	if(trim(document.login_form.ycode.value)=="")
	{
		alert("请输入验证码!");
		document.login_form.ycode.focus();
		return false
	}
	return true;
}