Unfortunately:

    400
    Bad Request
    Your request has been blocked by our server's security policies.

EDIT: Oh, I'm getting that even on their main page.

https://www.isitdownrightnow.com/phys.org.html says:

    Down Forever? The site has been unreachable for more than 120 days. If the site is live or if you have further information about the site status, please comment below...

This sounds pretty unlikely. I wonder what's up. Also I can reach it from my cell phone.

If it's useful, here [1] is the study.

[1] - https://www.sciencedirect.com/science/article/abs/pii/S09608...

Something isn't (or wasn't) right at your/their end. I can reach the site without issues right now.