In Google Scholar erfasste wissenschaftliche Volltexte sind mehr in der allgemeinen Websuche von Google abrufbar.

Aus den Kommentaren zu:
http://scholarlykitchen.sspnet.org/2015/02/18/what-would-it-cost-to-buy-everything/

"Case in point Google no longer indexing full text of scholarly articles in their general Google search results, and only doing so for Google Scholar, based on users either not clicking on academic papers or clicking and then rapidly going back to the search results for something else. [...]

The changes were announced in February 2013 on the private HighWire Forum for publishers that are on that platform. It was announced by a representative from Google Scholar. I’m not sure if I’m allowed to repost that here, and I haven’t seen it publicly stated anywhere. But it’s fairly easy to demonstrate if you have access to a recent journal article that’s limited to subscription access. Do a search on a sentence from the abstract and then do a search on text from deep within the article. Compare between Google and Google Scholar."

Update:
http://log.netbib.de/archives/2015/02/19/google-scholar-aufgewertet/