nextpage 分页有点奇怪。您必须解析帖子内容。这应该可以做到。

function get_nth_page($n=0,$content=\'\') {
  if (empty($content)) {
    global $post;
    $content = $post->post_content;
  }
  if (empty($content)) {
    return false;
  }
  $content = str_replace("\\n<!--nextpage-->\\n", \'<!--nextpage-->\', $content);
  $content = str_replace("\\n<!--nextpage-->", \'<!--nextpage-->\', $content);
  $content = str_replace("<!--nextpage-->\\n", \'<!--nextpage-->\', $content);
  $pages = explode(\'<!--nextpage-->\', $content);
  if (isset($pages[$n])) {
    return $pages[$n];
  }
}