I usually need to find some articles in other languages (French and German, etc). I googled the reference provided on the book but I seldom found what I need. For example, how can I find this article
What website should I use? I tried to use my university's library but I couldn't find any such articles.
On
Instead of searching for the article, see if your university has access to the journal in which the article is published. If you can login to the journal's website using your university credentials then they should have a database of all publications and you can find it there by tracking the year/volume number.
With the aid of Google ("elem math") to find the journal and then Zentralblatt to get the right page number, I found it here:
https://www.e-periodica.ch/digbib/view?pid=edm-001:1965:20#142
It's Zentralblatt (which gives limited but useful access to everybody) and AMS Math Reviews (if you are a member or have access via your institution) that are the real stars here: people that I talk to who work in Computer Science and many other disciplines are amazed to learn that mathematics has these wonderful resources that collate so much of the literature.