echo date("Ymd",strtotime("now")), "n";
    echo date("Ymd",strtotime("-1 week Monday")), "n";
    echo date("Ymd",strtotime("-1 week Sunday")), "n";
    echo date("Ymd",strtotime("+0 week Monday")), "n";
    echo date("Ymd",strtotime("+0 week Sunday")), "n";
 
    echo "*********第几个月:";
    echo date('n');
    echo "*********本周周几:";
    echo date("w");
    echo "*********本月天数:";
    echo date("t");
    echo "*********";
 
    echo '<br>上周起始时间:<br>';
    echo date("Y-m-d H:i:s",mktime(0, 0 , 0,date("m"),date("d")-date("w")+1-7,date("Y"))),"n";
    echo date("Y-m-d H:i:s",mktime(23,59,59,date("m"),date("d")-date("w")+7-7,date("Y"))),"n";
    
    echo '<br>本周起始时间:<br>';
    echo date("Y-m-d H:i:s",mktime(0, 0 , 0,date("m"),date("d")-date("w")+1,date("Y"))),"n";
    echo date("Y-m-d H:i:s",mktime(23,59,59,date("m"),date("d")-date("w")+7,date("Y"))),"n";
 
    echo '<br>上月起始时间:<br>';
    echo date("Y-m-d H:i:s",mktime(0, 0 , 0,date("m")-1,1,date("Y"))),"n";
    echo date("Y-m-d H:i:s",mktime(23,59,59,date("m") ,0,date("Y"))),"n";
    
    echo '<br>本月起始时间:<br>';
    echo date("Y-m-d H:i:s",mktime(0, 0 , 0,date("m"),1,date("Y"))),"n";
    echo date("Y-m-d H:i:s",mktime(23,59,59,date("m"),date("t"),date("Y"))),"n";
 
    $season = ceil((date('n'))/3);//当月是第几季度
    echo '<br>本季度起始时间:<br>';
    echo date('Y-m-d H:i:s', mktime(0, 0, 0,$season*3-3+1,1,date('Y'))),"n";
    echo date('Y-m-d H:i:s', mktime(23,59,59,$season*3,date('t',mktime(0, 0 , 0,$season*3,1,date("Y"))),date('Y'))),"n";
 
    $season = ceil((date('n'))/3)-1;//上季度是第几季度
    echo '<br>上季度起始时间:<br>';
    echo date('Y-m-d H:i:s', mktime(0, 0, 0,$season*3-3+1,1,date('Y'))),"n";
    echo date('Y-m-d H:i:s', mktime(23,59,59,$season*3,date('t',mktime(0, 0 , 0,$season*3,1,date("Y"))),date('Y'))),"n";

<?php
echo "今天:".date("Y-m-d")."<br>";
echo "昨天:".date("Y-m-d",strtotime("-1 day"));
echo "明天:".date("Y-m-d",strtotime("+1 day"));
echo "一周后:".date("Y-m-d",strtotime("+1 week"));
echo "一周零两天四小时两秒后:".date("Y-m-d G:H:s",strtotime("+1 week 2 days 4 hours 2 seconds"));
echo "下个星期四:".date("Y-m-d",strtotime("next Thursday"));
echo "上个周一:".date("Y-m-d",strtotime("last Monday"));
echo "一个月前:".date("Y-m-d",strtotime("last month"));
echo "一个月后:".date("Y-m-d",strtotime("+1 month"));
echo "十年后:".date("Y-m-d",strtotime("+10 year"));
?>