//获取时间
DateTime.Now.ToLongTimeString().ToString();   // 20:16:16
DateTime.Now.ToShortTimeString().ToString();   // 20:16
DateTime.Now.ToString("hh:mm:ss");        // 08:05:57
DateTime.Now.TimeOfDay.ToString();        // 20:33:50.7187500

//其他
DateTime.ToFileTime().ToString();       // 128650040212500000
DateTime.Now.ToFileTimeUtc().ToString();   // 128650040772968750
DateTime.Now.ToOADate().ToString();       // 39695.8461709606
DateTime.Now.ToUniversalTime().ToString();   // 2008-9-4 12:19:14

DateTime.Now.Year.ToString();          获取年份   // 2008
DateTime.Now.Month.ToString();      获取月份   // 9
DateTime.Now.DayOfWeek.ToString(); 获取星期   // Thursday
DateTime.Now.DayOfYear.ToString(); 获取第几天   // 248
DateTime.Now.Hour.ToString();          获取小时   // 20
DateTime.Now.Minute.ToString();     获取分钟   // 31
DateTime.Now.Second.ToString();     获取秒数   // 45

//n为一个数,可以数整数,也可以事小数
dt.AddYears(n).ToString();   //时间加n年
dt.AddDays(n).ToString();   //加n天
dt.AddHours(n).ToString();   //加n小时
dt.AddMonths(n).ToString();   //加n个月
dt.AddSeconds(n).ToString();   //加n秒
dt.AddMinutes(n).ToString();   //加n分