一年中第几周

System.Globalization.CultureInfo ci = new System.Globalization.CultureInfo("en-US");
            System.Globalization.Calendar cal = ci.Calendar;
            System.Globalization.CalendarWeekRule cwr = ci.DateTimeFormat.CalendarWeekRule;
            System.DayOfWeek dow = ci.DateTimeFormat.FirstDayOfWeek;
            currentWeek = cal.GetWeekOfYear(System.DateTime.Now, cwr, dow);