Women have been rapidly climbing the employment and wage ladders in recent decades. But only a small fraction have made it to the top rungs — and their progress may be slowing. New research shows that after making big strides in the 1980s and ’90s, the number of women breaking into the top 1 percent of earners has stalled. Women account for only 16 percent of the 1 percent, a number that has remained essentially flat over the past decade, according to a paper by three economists.