1) regular web: check for currently working domains [here](https://wadauk.github.io/scihub_ck/index.html)
2) These IP addresses rarely change: http://22.214.171.124/ and http://126.96.36.199/
3) https://scihub22266oqcxt.onion (only via Tor; spotty access)
4) Telegram Messenger: send your DOI to @scihubot
If none of the “regular web” links are working, your DNS records may be censored. Try using Tor instead.
If nothing works, the server is down. This rarely lasts longer than one day.