You can use the "add RUG proxy" bookmarklet on any page you are visiting to view it through the university proxy. If we have a subscription to the site, this yields full-text access. If not, the bookmarklet has no effect.
(For more on bookmarklets, see e.g. this)

Note that if you use Google Scholar, you can often tell it what institution you are from, to have it link you to articles via your institution's proxy. Note that this mechanism is not aware of subscriptions, so such links to a lookup do not necessarily lead to full text.
(configure this via Scholar Preferences, go to Library Links and search for you institution's name, then Save)