No, there is no way to restrict google scholar searches to only open-access papers.
However, you have several options, to ensure that you can access pay-for-access journals that your institution has subscriptions for, even when you're off-campus. This neatly short-circuits the question of having to search only open-access journals. And see also the section below on "Hosting on servers other than the journal itself", which will allow you to find open-access copies of papers that are in pay-to-access journals, by looking on author's homepages and similar.
Shibboleth / Athens login
The login name and password you use for your campus network, may also serve as your login and password for one of the access aggregators, such as Shibboleth or Athens. So once you're at the online journal page of the paper you're after, look for "institutional login" or "login", and then search for the login details of your aggregator, and then for your institution. For example, most UK universities are part of the Shibboleth network, and get access via the UK Access Management Federation. So the login route is:
- a link called something like
institutional login on the journal page
- a dropdown for UK Access Management Federation
- a select-box to pick the specific university
- university login and password
Hosting on servers other than the journal itself
Once you've done your usual search, and got the title of a potentially-interesting paper, then you can start looking for PDFs of it. First do a plain (not scholar) google search for the title, in double-quotes, and
filetype:pdf. So if you were looking for the paper "Ninja Google skills", then you'd google for
"Ninja Google skills" filetype:pdf
If that doesn't work, check whether the paper is hosted on:
- the university homepages of any of the authors
- the preprint server at each of their universities
- any subject-wide preprint archive for your subject area
Or email the author on the paper who's nominated as first contact, asking them for a preprint copy of the paper. A couple of sentences about why you're interested, and how you'll use it, will help.
Remote access to the campus network
Some people with this problem will have one or more means to access their campus network (although you do not. This answer is to help others as well as you, and their circumstances will not be identical to yours); a quick chat with one of the librarians, and someone in the university IT support team, should help clarify:
- VPN into the campus network, then search; or
- SSH into the campus network, then search; or
- log in to the university library network web page, and search from there.
Failing all that, get creative
For some of the following, you'll need to check your university's terms and conditions, and official guidelines, to ensure that you play within the letter and the spirit of the rules:
- Set up an in-campus server process that will receive remotely-submitted requests, search for a paper, and download it, and make it available to you. You might do this via a web-page, email, or Dropbox.
- Share a Dropbox folder or similar with colleagues, and arrange that whenever one of you is on campus, and has a spare few minutes, you'll look for new requests in the shared folder, and if you find any, you'll download the paper and pop it in the Dropbox.
- Ask your supervisor / department head (as appropriate) to mention to a very senior administrator that the University is failing its staff and postgrads in a key area, and that some form of off-site access is just part of being a university in the 21st Century.