It appears that at least two mobile internet providers are blocking access to NIH studies. For instance, I was unable to load this from my phone using 4G and had to connect using separate wifi. Several others have confirmed this. For instance:
https://www.ncbi.nlm.nih.gov/m/pubmed/21716201/
If you're unable to view the link, it discusses the carcinogenic effects of low intensity microwave radiation from devices such as mobile phones and wireless modems.
Edit: Appears that all NIH studies are blocked, e.g.,
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3746332/
So perhaps it's a DDOS prevention routing issue.