  I propose the coefficient, $t_h$, and its modification $N_t$ which in a
simple way reflect dynamics of scientific activity of an individual researcher.
I determine $t_h$ as a time period (from some moment in the past till the
present moment) during which papers responsible for 1/2 of the total citation
index were published. Parameter $N_t$ represents average of the citation index
over this period: $N_t={\mathrm{C.I.}}/2t_h$.
