http://us63bgjkxwpyrpvsqom6kw3jcy2yujbplkhtzt64yykt42ne2ms7p4yd.onion
Don't feel bad about using it; governments / medical institutions are basing some decisions on the paid studies - and you have the right to know just how solid they are. To download a study, you usually just need its PMID number. Technology Ciphers by Ritter - Best cryptography resource out there, by a mile.