lucy24 - 12:46 am on May 1, 2013 (gmt 0)
If I understand your question correctly, you're looking for something that can't be done.
A page is, by definition, requested before its supporting files. So at the time the request is made there is no way to tell whether it will be followed by other requests. You can look at other aspects of the request header, but each request is an island.
If you're talking about getting information after the fact from raw logs, you don't need to know ahead of time whether it was human or robot, because you can look at the package. Up until a few years ago, all you needed to look for was a request for the favicon. Robots that ask for this are few and far between, and most are known quantities that you can filter out.
Now, thanks to all those ### mobiles, it's trickier. Add requests for apple-touch-icon to the list. Then look for packages, such as search-engine query followed by requests for supporting files. There are a few other robot flags that jump out at you in logs. One I use is the auto-referer: any request for a page that names the page itself as referer. This of course only works if your pages don't link to themselves-- no active "home" link on the home page, that kind of thing. Internal fragment links in # are OK because your server won't see them. Another that works for me but may not work for everyone is requests giving my front page as referer when the page isn't linked from the front page-- in my case, everything but top-level directory index files.