  Temperature dependence of resistivity of single crystals of
Fe$_{1-x}$Co$_x$Se and FeSe$_{1-y}$S$_y$ is studied in detail under zero and
high magnetic field (magnetoresistance), the latter of which enables to monitor
the temperature ($T$) evolution of resistivity below the onset of
superconducting transition temperature ($T_{\rm c}$). In FeSe$_{1-y}$S$_y$,
$T$-linear dependence of resistivity is prominent in $y$ = 0.160 below 40 K,
whereas it changes to a Fermi-liquid(FL)-like $T^2$ one below 10 K in $y$ =
0.212. These suggest that the quantum critical point (QCP) originating from the
electronic nematicity resides around $y$ = 0.160 and the fluctuation in QCP
gives rise anomalous $T$-linear dependence in resistivity in a wide $T$ range.
In Fe$_{1-x}$Co$_x$Se, resistivity gradually changes from linear- to quadratic-
$T$-dependent one at low temperatures in the range between $x$ = 0.036 and
0.075. These could be interpreted by scenarios of both the nematic QCP and the
crossover in the ground states between the orthorhombic nematic phase and the
tetragonal phase. The anomalies found as $T$-linear resistivity are discussed
in terms of orbital and spin fluctuation arising from the nematic QCP.
