json_decode 确定是否以数组而不是对象的形式返回结果.由于将其设置为true，因此结果是数组而不是对象.

The second parameter of json_decode determines whether to return the result as an array instead of an object. Since you set it to true your result is an array and not an object.

$content = $final_res['articles'][0]['Content'];