How to get academic search engines only search in open access journals? Sometimes I work from home, and for security reasons it is not possible to connect to the campus computers. I use Google Scholar for finding papers and so, but from home, most of the journals can not be accessed.

Is it there some way in which Google Scholar or another academic search engine searches only in open access journals?

PS1: There is no way in which I can access my campus, really.

PS2: OK, I will give more details, since it seems that PS1 is not clear enough. I am working with other collaborators that are not affiliated to any University. I could do VPN and similar but I can not pass them such information, or any other way of passwords or access to the campus, etc. We can only work with the open access papers they find. If the interesting papers are under a paywall, then they are useless for us. I hope this clarifies my questions, and thank everybody for the useful comments.
I'm not sure, whether you really meant open access journals, because when I'm searching at home and I'm too lazy to use the VPN of our university, I'm usually interested in publications I can access.

I wouldn't rely on Google Scholar alone, because I'm not sure whether they filter the results. When you study the advanced search of google a bit, you'll see, that some of the switches are really nice. One really important switch is the -filetype option. If you search for instance for image segmentation in Google Scholar you get instantly only results with a downloadable pdf file if you use

image segmentation filetype:pdf


Even more handy becomes this approach in a two step method. As you know, when you "put something in quotes" in google, you search for the exact string. This can be used to do the following:


find some preview of the article you want to download. 
choose a very specific part of a sentence there
search for this part and use the filetype option


Non-scientific example: Sometimes I'm searching for piano notes of some popular songs and since everyone tries to make money with this, you often won't find a free, downloadable version. Therefore, I first search for something like "sheet music evanescence my immortal" and look at one of the first links, where you usually can see one sample page. Then I see, what's on the page and I use this information to adjust my search

"My immortal" "I'm so tired of" "Slowly and freely" filetype:pdf


and the first hit is a high-quality pdf with all pages.

The same approach sometimes works for scientific publications, because most scientists put their publication on their website. So while you have to pay on the journal website, you may get it for free somewhere else.