“Article not found” for these 3 DOI (they are old articles, not new)

Hi everybody, these are the 2 DOI (2, not 3, sorry) :



I know Sci-Hub won’t work for recent articles, but these are supposedly older than that.OpenAccessButton doesn’t work either.And authors don’t answer for the moment.

Can anybody please help ? I really need them for my ongoing research. Thanks in advance !