I'm not sure if the general public can acccess this at the moment, but crossref.org and google have got together to provide a pilot full text searching of scholarly journals for 29 leading journal papers. For more info, click here: http://www.crossref.org/crossrefsearch.html

I can't seem to find an entry page for the cross-ref search engine, but I got to it through the IEEE Xplore cross-ref page, but I'm not sure if that it is only available because of QUT's subscription to IEEE:
http://ieeexplore.ieee.org/search/crefsearch.html

- David
cebidae.blogspot.com

The text above is also on my blog at
http://cebidae.blogspot.com/2004/10/google-fulltext-research-paper-search.html

Currently, CrossRef Search full text search is accessed via any of the 29 member publications' web pages. eg 'Nature's' CrossRef Search is at <http://www.nature.com/dynasearch/xrs/>. It seems to work OK, with no restrictions. In fact, when complete, CrossRef Search will be freely available to (eg) any library to place a CrossRef Search box on their website (it will have a Google logo on it!).