Where to find digitized old papers on the internet?

Suppose the question is "How can I find old papers?" ... (so old that they are not on-line).

If it is "not even in the library" ... then see a librarian. He/she can get it by interlibrary loan.

Perhaps it is worth mentioning that several important journals have been digitized by GDZ. It is one of reasonable places where to look for older papers. (If you can't find it through the subscription of your institution.)

Here is list of mathematical journals available at GDZ.

In fact, Google Scholar search finds several versions of the paper mentioned in the question. One of them is eudml link which links further to GDZ.

Several other reasonable possibilities are mentioned in the answers to this question: Finding a paper.