$(function(){
    $(".expand").bind("click",function(){
      $(this).closest('div.n_content').show();
    });
});


<div class='content_class'>
      <div class='n_intro'>intro</div>
      <div class='n_content'>content</div>
      <p><a href='#' class='expand'>expand</a></p>
</div>
<div class='content_class'>
      <div class='n_intro'>intro</div>
      <div class='n_content'>content</div>
      <p><a href='#' class='expand'>expand</a></p>
</div>
<div class='content_class'>
      <div class='n_intro'>intro</div>
      <div class='n_content'>content</div>
      <p><a href='#' class='expand'>expand</a></p>
</div>