  We infer the period ($P$) and size ($R_p$) distribution of Kepler transiting
planet candidates with $R_p\ge 1 R_{\rm Earth}$ and $P < 250$ days hosted by
solar-type stars. The planet detection efficiency is computed by using measured
noise and the observed timespans of the light curves for $\sim 120,000$ Kepler
target stars. We focus on deriving the shape of planet period and radius
distribution functions. We find that for orbital period $P>10$ days, the planet
frequency d$N_p$/d$\log$P for "Neptune-size" planets ($R_p = 4-8 R_{\rm
Earth}$) increases with period as $\propto P^{0.7\pm0.1}$. In contrast,
d$N_p$/d$\log$P for "super-Earth-size" ($2-4 R_{\rm Earth}$) as well as
"Earth-size" ($1-2 R_{\rm Earth}$) planets are consistent with a nearly flat
distribution as a function of period ($\propto P^{0.11\pm0.05}$ and $\propto
P^{-0.10\pm0.12}$, respectively), and the normalizations are remarkably similar
(within a factor of $\sim 1.5$ at $50 $ days). Planet size distribution evolves
with period, and generally the relative fractions for big planets ($\sim 3-10
R_{\rm Earth}$) increase with period. The shape of the distribution function is
not sensitive to changes in selection criteria of the sample. The implied
nearly flat or rising planet frequency at long period appears to be in tension
with the sharp decline at $\sim 100$ days in planet frequency for low mass
planets (planet mass $m_p < 30 M_{\rm Earth}$) recently suggested by HARPS
survey. Within $250$ days, the cumulative frequencies for Earth-size and
super-Earth-size planets are remarkably similar ($\sim 28 %$ and $25%$), while
Neptune-size and Jupiter-size planets are $\sim 7%$, and $\sim 3%$,
respectively. A major potential uncertainty arises from the unphysical impact
parameter distribution of the candidates.
