怎样只改变某个区域内的链接打开方式？

1<a href="1.htm">正常链接</a>

1<base target="_blank"/>

1<a href="2.htm">弹出窗口链接</a>

1<a href="2.htm">弹出窗口链接</a>

1<a href="2.htm">弹出窗口链接</a>

1<base target="_self"/>

1<a href="3.htm">正常链接</a>