The Nikkei stock index briefly topped the 37,000-point threshold for the first time in 34 years on Friday, buoyed by a weaker yen and robust earnings, although gains were limited as some investors moved to lock in recent gains. The 225-issue Nikkei Stock Average ended up 34.14 points, or 0.09 percent, from Thursday at 36,897.42, its highest close since Feb. 19, 1990. The broader Topix index finished 4.75 points, or 0.19 percent, lower at 2,557.88. On the top-tier Prime Market, gainers were led by oil and coal, and nonferrous metal issues, while marine transportation, and textile and apparel sh…