采集错误，请高手指点

<ul class="news-content">
<li>
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我的采集规则是：
 $p='/<ul class="news-content">';
 $p.='<li>\s+<span class="topnews_desc">(.*)<\/span>\s+<a class="(.*)" href="(.*)" target="_blank" title="(.*)"><span>(.*)<\/span><\/a>\s+<\/li>';
 $p.='<\/ul>/';
因为每块都是用UL来划分的，所以把UL加进去应该怎么写