DateTime dtNow = DateTime.Now;
            string mon1 = dtNow.ToString("yyyy-MM-dd hh:mm:ss");//MM为月份，hh为12小时制
            string mon2 = dtNow.ToString("yyyy-mm-dd HH:mm:ss");//mm为分钟，HH为24小时制
            Console.WriteLine(mon1);
            Console.WriteLine(mon2);