通过网上咨询使用这个选择器便很容易的解决。特此记录一下。
下面是主要的代码
js脚本：
复制代码 代码如下:
<script type="text/javascript">
$(document).ready(
function () {
//每隔五行给li加一个样式
$('.article_li li:nth-child(5n)').addClass('liborder');
$('.article_li li:last').addClass('liborder');
}
);
</script>

html代码：
复制代码 代码如下:
<ul class="article_li">
<li>
<label class="datename">
<span>2010-06-12 08:37:59 </span>
</label>
<a href="/a/xinwenzixun/caishuidongtai/20100612/2323.html">物业税:长沙暂不试点物业税:长沙暂不试点</a>
</li>
<li>
<label class="datename">
<span>2010-06-12 08:37:59 </span>
</label>
<a href="/a/xinwenzixun/caishuidongtai/20100612/2323.html">物业税:长沙暂不试点</a> </li>
<li>
<label class="datename">
<span>2010-06-12 08:37:59 </span>
</label>
<a href="/a/xinwenzixun/caishuidongtai/20100612/2323.html">物业税:长沙暂不试点</a> </li>
<li>
<label class="datename">
<span>2010-06-12 08:37:59 </span>
</label>
<a href="/a/xinwenzixun/caishuidongtai/20100612/2323.html">物业税:长沙暂不试点</a> </li>
<li>
<label class="datename">
<span>2010-06-12 08:37:59 </span>
</label>
<a href="/a/xinwenzixun/caishuidongtai/20100612/2323.html">物业税:长沙暂不试点</a> </li>
<li>
<label class="datename">
<span>2010-06-12 08:37:59 </span>
</label>
<a href="/a/xinwenzixun/caishuidongtai/20100612/2323.html">物业税:长沙暂不试点</a> </li>
<li>
<label class="datename">
<span>2010-06-12 08:37:59 </span>
</label>
<a href="/a/xinwenzixun/caishuidongtai/20100612/2323.html">物业税:长沙暂不试点</a> </li>
<li>
<label class="datename">
<span>2010-06-12 08:37:59 </span>
</label>
<a href="/a/xinwenzixun/caishuidongtai/20100612/2323.html">物业税:长沙暂不试点</a> </li>
<li>
<label class="datename">
<span>2010-06-12 08:37:59 </span>
</label>
<a href="/a/xinwenzixun/caishuidongtai/20100612/2323.html">物业税:长沙暂不试点</a> </li>
<li>
<label class="datename">
<span>2010-06-12 08:37:59 </span>
</label>
<a href="/a/xinwenzixun/caishuidongtai/20100612/2323.html">物业税:长沙暂不试点</a> </li>
<li>
<label class="datename">
<span>2010-06-12 08:37:59 </span>
</label>
<a href="/a/xinwenzixun/caishuidongtai/20100612/2323.html">物业税:长沙暂不试点</a> </li>
<li>
<label class="datename">
<span>2010-06-12 08:37:59 </span>
</label>
<a href="/a/xinwenzixun/caishuidongtai/20100612/2323.html">物业税:长沙暂不试点</a> </li>
<li>
<label class="datename">
<span>2010-06-12 08:37:59 </span>
</label>
<a href="/a/xinwenzixun/caishuidongtai/20100612/2323.html">物业税:长沙暂不试点</a> </li>
<li>
<label class="datename">
<span>2010-06-12 08:37:59 </span>
</label>
<a href="/a/xinwenzixun/caishuidongtai/20100612/2323.html">物业税:长沙暂不试点</a> </li>
<li>
<label class="datename">
<span>2010-06-12 08:37:59 </span>
</label>
<a href="/a/xinwenzixun/caishuidongtai/20100612/2323.html">物业税:长沙暂不试点</a> </li>
<li>
<label class="datename">
<span>2010-06-12 08:37:59 </span>
</label>
<a href="/a/xinwenzixun/caishuidongtai/20100612/2323.html">物业税:长沙暂不试点</a> </li>
<li>
<label class="datename">
<span>2010-06-12 08:37:59 </span>
</label>
<a href="/a/xinwenzixun/caishuidongtai/20100612/2323.html">物业税:长沙暂不试点</a> </li>
<li>
<label class="datename">
<span>2010-06-12 08:37:59 </span>
</label>
<a href="/a/xinwenzixun/caishuidongtai/20100612/2323.html">物业税:长沙暂不试点</a> </li>
<li>
<label class="datename">
<span>2010-06-12 08:37:59 </span>
</label>
<a href="/a/xinwenzixun/caishuidongtai/20100612/2323.html">物业税:长沙暂不试点</a> </li>
<li>
<label class="datename">
<span>2010-06-12 08:37:59 </span>
</label>
<a href="/a/xinwenzixun/caishuidongtai/20100612/2323.html">物业税:长沙暂不试点</a> </li>
<li>
<label class="datename">
<span>2010-06-12 08:37:59 </span>
</label>
<a href="/a/xinwenzixun/caishuidongtai/20100612/2323.html">物业税:长沙暂不试点</a> </li>
<li>
<label class="datename">
<span>2010-06-12 08:37:59 </span>
</label>
<a href="/a/xinwenzixun/caishuidongtai/20100612/2323.html">物业税:长沙暂不试点</a> </li>
<li>
<label class="datename">
<span>2010-06-12 08:37:59 </span>
</label>
<a href="/a/xinwenzixun/caishuidongtai/20100612/2323.html">物业税:长沙暂不试点</a> </li>
</ul>

具体的用法这里就不写了，大家可以参考
https://www.jb51.net/css/28294.html 
https://www.jb51.net/article/23617.htm
效果图如下：