You can do this by using content regions in the head, in exactly the same way as you would in the body of the page. eg, In your masterpage:
<head>
<link type="text/css" rel="stylesheet" href="/styles/common1.css" />
<script type="text/javascript" src="/scripts/common1.js"></script>
<asp:contentplaceholder id="ExtraStylesAndScripts" runat="server" />
</head>
And then in the page itself just something like:
<asp:content contentplaceholderid="ExtraStylesAndScripts" runat="server">
<link type="text/css" rel="stylesheet" href="/styles/extra1.css" />
<link type="text/css" rel="stylesheet" href="/styles/extra2.css" />
<script type="text/javascript" src="/scripts/extra1.js"></script>
<script type="text/javascript" src="/scripts/extra2.js"></script>
</asp:content>
与恶龙缠斗过久,自身亦成为恶龙；凝视深渊过久,深渊将回以凝视…
