PHP正则表达式截取字符串求助！！！！

"=?gb2312?xPrU2rPM0PLUscGqus+/qreizfgod3d3LnB1ZG4uY29tKbXE1cq6xdLRv6o=?= =?gb2312?B?zag=?="假设我有这样的一个字符串，我想用正则将=??=之间的字符截取出来，因为它有两部分=??=这样的，要怎样写才对？

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$str = '"=?gb2312?xPrU2rPM0PLUscGqus+/qreizfgod3d3LnB1ZG4uY29tKbXE1cq6xdLRv6o=?= =?gb2312?B?zag=?="简游消拦知';
preg_match_all('磨稿/(?==\?)[^\1]+?\?=/', $str, $matches);
print_r($matches);

结果:

Array
(
[0] => Array
(
[0] => =?gb2312?xPrU2rPM0PLUscGqus+/qreizfgod3d3LnB1ZG4uY29tKbXE1cq6xdLRv6o=?=
[1] => =?gb2312?B?zag=?=
)

)

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$str = "=?gb2312?xPrU2rPM0PLUscGqus+/渣型雹租咐qreizfgod3d3LnB1ZG4uY29tKbXE1cq6xdLRv6o=?= =?gb2312?B?zag=?=";
preg_match_all('\如帆=\?.+\?\=', $str, $arr);
print_r($arr);

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(?:=\?).*?(?:\?=)
这样写

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