You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'ORDER BY `year`, issue ) QQ WHERE `year`<2100 ORDER BY modified DESC LIMIT 0, 5' at line 1 Bibliographies | Miko Flohr
 

Proceedings of the National Academy of Sciences of the United States of America

Bettencourt, L., J. Lobo, D. Helbing, Chr. Kühnert and G.B. West (2007). ‘Growth, innovation, scaling, and the pace of life in cities’. PNAS 104.17: 7301–7306.
Turchin, P. and W. Scheidel (2009). ‘Coin hoards speak of population declines in Ancient Rome’. PNAS 106.41: 17276–17279.
McConnell, J, A. Wilson, M. Arienzo, N. Chellman, S. Eckhardt, E. Thompson, M. Pollard and J. Steffensen (2018). ‘Lead pollution recorded in Greenland ice indicates European emissions tracked plagues, wars, and imperial expansion during antiquity’. PNAS 115.22: 5726–5731.