The drastic rise of the proton structure function
$F_2(x,Q^2)$ when the Bj\"orken variable $x$ decreases, seen at HERA for
a large span of $Q^2$, may be damped when $x\to 0$ and $Q^2$ increases
beyond $\sim$ several hundreds \g2. This phenomenon observed in the
Regge type models is discussed in terms of the effective Pomeron
intercept and of the derivative $B_x=\partial{\ell n
F_2(x,Q^2)}/\partial{\ell n(1/x)}$. The method of the overlapping bins
is used to extract the derivatives $B_x$ and $B_Q=\partial{\ell n
F_2(x,Q^2)}/\partial{Q^2}$ from the data on $F_2$ for $6.0\cdot
10^{-5}\le x\le 0.61$ and $1.2 \le Q^2$ (\g2) $\le 5000$. It is shown
that the extracted derivatives are well described by recent Regge models
with the Pomeron intercept equal one.

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