The journal this citation is taken from is Unione Matematica Italiana. Bollettino. A. The electronic text of this bulletin is not available online. If you are based at Cambridge, Glasgow or Edinburgh Universities then you can find a copy in their University libraries.
If you go to this link you can find the closest library to you that has a copy.
Otherwise, it's on Google books at , which might give you more information on how you might get a copy.