<asp:LinkButton runat="server" Text="Show" OnClick="lbShow_Click" OnClientClick="cs()" />

 function cs() {
        return false;
    }

<script type="text/javascript">
    function cs() {
        return false;
    }

    $(document).ready(function () {
        $(".calendar").datepicker({ dateFormat: "dd.mm.yy",
            selectOtherMonths: true,
            showOtherMonths: true
        });
    });

</script>