string s="uid=aaaaaaaaaaaa</a>||||||||||||||Uid=bbbbbbbbbbbbbbbbbb</a>||||||||||||||Uid=cccccccccccccc</a>||||||||||||||Uid=dddddddddddddddd</a>";
//temp 存放匹配结果
string temp="";
//results 正则捕获结果集合
MatchCollection results = Regex.Matches(s,"uid=(?<txt>.*?)</a>",RegexOptions.IgnoreCase);
//遍历results集合
foreach(Match m in results)
{
temp+=m.Groups["txt"].ToString()+"<br/>";//将m中命名为txt的组的捕获内容拼接到temp
}
//输出结果
Response.Write(temp);
Response.End();