I also think that converting people to a subscription would be more effective if an abstract were presented, rather than a page with only a login/password/registration required.
I think that is a key point to this discussion.
One might purchase a subscription or an article if they have a pretty good idea of what it contains. But with no way to know that at all, other than it somehow matched a search query, I find it hard to believe anyone would purchase it sight unseen.
I once purchased an article from Northern Light, but they had a short abstract. I was actually searching for my name, and NL came up with something that I could tell was about me, but I didn't recognize what it was. Turned out it was an old article from a magazine where a reporter had quoted me. Was worth the buck or two to find out what it was. However, had there not been any abstract, there's no way I would have spent the few bucks to find out what it was. Could have been something that had nothing to do with me.