php 获取今天，本周，本月，三个月内，半年内，今年的开始和结束时间

$now = time(); 
        //今天
        $today_audit_num = 0;
        $today_use_num = 0;
        $beginTime = date('Y-m-d 00:00:00', $now);  
        $endTime = date('Y-m-d 23:59:59', $now);  

        //本周
        $week_audit_num = 0;
        $week_use_num = 0;
        $time = '1' == date('w') ? strtotime('Monday', $now) : strtotime('last Monday', $now);  
        $beginTime = date('Y-m-d 00:00:00', $time);  
        $endTime = date('Y-m-d 23:59:59', strtotime('Sunday', $now));  

        //本月
        $month_audit_num = 0;
        $month_use_num = 0;
        $beginTime = date('Y-m-d 00:00:00', mktime(0, 0, 0, date('m', $now), '1', date('Y', $now)));  
        $endTime = date('Y-m-d 23:39:59', mktime(0, 0, 0, date('m', $now), date('t', $now), date('Y', $now))); 

        //三个月内
        $three_month_audit_num = 0;
        $three_month_use_num = 0;
        $time = strtotime('-2 month', $now);  
        $beginTime = date('Y-m-d 00:00:00', mktime(0, 0,0, date('m', $time), 1, date('Y', $time)));  
        $endTime = date('Y-m-d 23:39:59', mktime(0, 0, 0, date('m', $now), date('t', $now), date('Y', $now)));  ;

        //半年内
        $half_year_audit_num = 0;
        $half_year_use_num = 0;
        $time = strtotime('-5 month', $now);  
        $beginTime = date('Y-m-d 00:00:00', mktime(0, 0,0, date('m', $time), 1, date('Y', $time)));  
        $endTime = date('Y-m-d 23:39:59', mktime(0, 0, 0, date('m', $now), date('t', $now), date('Y', $now)));  

        //今年
        $year_audit_num = 0;
        $year_use_num = 0;
        $beginTime = date('Y-m-d 00:00:00', mktime(0, 0,0, 1, 1, date('Y', $now)));  
        $endTime = date('Y-m-d 23:39:59', mktime(0, 0, 0, 12, 31, date('Y', $now)));