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True that vast information resources from research conducted with publicly(at times) funded money is hidden behind paywalls like the one from ACM. Here is an old discussion about that topic

http://news.ycombinator.com/item?id=2135423

Anyways, most of the researchers will have a pdf version of their paper on their site. Googling the first author's name or the paper title generally throws the desired result most of the times. Also, as mentioned in another comment Google scholar does show a PDF link on the right if it finds one.

Try searching for the title on http://scholar.google.com ― I've found quite a few papers that were behind pay walls using it.

[EDIT] I've not found the papers listed by the OP but other papers in the past.

[EDIT 2] Oops the OP in fact has linked to Google Scholar. My bad. :)

[EDIT 3] Ah in the search result, on the right there should be a link like "[PDF] from ethz.ch".

You can also try using Google's filetype operator, for example:

filetype:pdf "Maximizing the spread of influence through a social network"

And if it's not available online, many researchers will send you a copy of the pdf if you send them a nice email.

If there is a university near you, go to the library and use the computers there.