You could use a ScriptManager
:
<asp:ScriptManager ID="ScriptManager1" runat="server">
<Scripts>
<asp:ScriptReference Path="https://stackoverflow.com/questions/697660/~/jquery.js" />
</Scripts>
</asp:ScriptManager>
EDIT: If you absolutely need this in your <head>
section, you could do something like:
<head>
<script type="text/javascript"
src="https://stackoverflow.com/questions/697660/<%= Page.ResolveClientUrl("https://stackoverflow.com/questions/697660/~/jquery.js") %>"></script>
</head>
EDIT 2: According to the comments, if you are observing that
The Controls collection cannot be modified because the control contains code blocks (i.e. <% … %>)
you may need to change the above to use the data-binding syntax:
<head>
<script type="text/javascript"
src="<%# Page.ResolveClientUrl("https://stackoverflow.com/questions/697660/~/jquery.js") %>"></script>
</head>