  We present a study of molecular outflows using six molecular lines (including
12CO/13CO/C18O/HCO+(J = 1-0) and SiO/CS(J = 2-1)) toward nine nearby high-mass
star-forming regions with accurate known distances. This work is based on the
high-sensitivity observations obtained with the 14-m millimeter telescope of
Purple Mountain Observatory Delingha (PMODLH) observatory. The detection rate
of outflows (including 12CO, 13CO, HCO+, and CS) is 100\%. However, the
emission of SiO was not detected for all sources. The full line widths ($\Delta
V$) at 3$\sigma$ above the baseline of these molecular lines have the
relationship $\Delta V_{\rm ^{12}CO} > \Delta V_{\rm HCO^{+}} > \Delta V_{\rm
CS} \approx \Delta V_{\rm ^{13}CO} > \Delta V_{\rm ^{18}CO}$. 12CO and HCO+ can
be used to trace relatively high-velocity outflows, while 13CO and CS can be
employed to trace relatively low-velocity outflows. The dynamical timescales of
the 13CO and CS outflows are longer than those of the 12CO and HCO+ outflows.
The mechanical luminosities, masses, mass-loss rates and forces of all outflows
(including 12CO, 13CO, HCO+, and CS) are correlated with the bolometric
luminosities of their central IRAS sources.
