You cannot control the new window's size in pure HTML. You'll have to use either an onclick handler to do a window.open via javascript, passing the new window's size to that function, or more preferrably in your case, use a resize function in the target page to increase the new window to the current screen size.
However, I feel compelled to advise against doing either. It's a non-standard (common, but non-standard) UI experience and can be incredibly frustrating, especially in browsers that open links targeting "_blank" as tabs rather than new windows.
Example of an onclick handler:
<a href="somepage.html" onclick="window.open('somepage.html', 'newWindowId', 'width='+screen.width+',height='+screen.height); return false;">click here</a>