function openwin(url, width, height) {
    var maxWidth = screen.width - (screen.width - screen.availWidth) * 2;
    var maxHeight = screen.height - (screen.height - screen.availHeight) * 2;
    if (width > maxWidth) {
        width = maxWidth;
    }
    if (height > maxHeight) {
        height = maxHeight;
    }
    var left = (screen.width - width) / 2;
    var top = (screen.height - height) / 2;
    window.open(url,"_blank","toolbar=0,location=0,directories=0,status=0,menubar=0,scrollbars=1,resizable=1,copyhistory=0,left=" + left + ",top=" + top + ",height=" + height + ",width=" + width);
}