1991
January January; 138 (1): 1 - 257	February February; 138 (2): 261 - 513	March March; 138 (3): 515 - 780
April April; 138 (4): 781 - 1057	May May; 138 (5): 1059 - 1291	June June; 138 (6): 1293 - 1555
July July; 139 (1): 1 - 241	August August; 139 (2): 245 - 466	September September; 139 (3): 469 - 696
October October; 139 (4): 701 - 957	November November; 139 (5): 961 - 1189	December December; 139 (6): 1195 - 1513