base标签需要放在head标签里，作用是让body标签里的所有a标签执行base标签里的指令
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
<base target="_blank">
</head>
<body>
<a href="http://news.baidu.com/">新闻</a>
<a href="https://www.hao123.com/">hao123</a>
<a href="https://map.baidu.com/">地图</a>
<a href="http://v.baidu.com/">视频</a>
<a href="https://tieba.baidu.com/index.html?traceid=">贴吧</a>
<a href="http://xueshu.baidu.com/">学术</a>
</body>
</html>
假链接：表面是超链接，但是无法链接到某个网页
"#"：点击假链接后，会回到页面顶部
"javascript:"：点击假链接后，没有任何反应
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<h2>页面顶部</h2>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<a href="#">假链接1</a>
<a href="javascript:">假链接2</a>
</html>