We introduce two new measures of the performance of a scientist. One measure, referred to as the hα-index, generalizes the well-known h-index or Hirsch index. The other measure, referred to as the gα-index, generalizes the closely related g-index. We analyze theoretically the relationship between the hα- and gα-indices on the one hand and some simple measures of scientific performance on the other hand. We also study the behavior of the hα- and gα-indices empirically. Some advantages of the hα- and gα-indices over the h- and g-indices are pointed out.