1991
January January; 57 (1): 1 - 331	February February; 57 (2): 333 - 624	March March; 57 (3): 625 - 891
April April; 57 (4): 893 - 1276	May May; 57 (5): 1277 - 1579	June June; 57 (6): 1581 - 1872
July July; 57 (7): 1873 - 2108	August August; 57 (8): 2109 - 2445	September September; 57 (9): 2447 - 2781
October October; 57 (10): 2783 - 3055	November November; 57 (11): 3057 - 3404	December December; 57 (12): 3405 - 3683