  Within a quark combination model, we study systematically the yields and
rapidity spectra of various hadrons in central Au+Au collisions at
$\sqrt{s_{NN}}= 200$ GeV. We find that considering the difference in rapidity
between net-quarks and newborn quarks, the data of multiplicities, rapidity
distributions for $\pi^{\pm}$, $K^{\pm}$, $p(\bar{p})$ and, in particular the
ratios of charged antihadron to hadron as a function of rapidity, can be well
described. The effect of net-quarks on various hadrons is analysed, and the
rapidity distributions for $K^{0}_{s}$, $\Lambda(\bar{\Lambda})$,
$\Sigma^{+}(\bar{\Sigma}^{_-})$, $\mathrm{\Xi^{-}}$ ($\mathrm{\bar{\Xi}^{_+}}$)
and $\mathrm{\Omega^{-}}(\mathrm{\bar{\Omega}}^{_+})$ are predicted. We discuss
the rapidity distribution of net-baryon, and find that it reflects exactly the
energy loss of colliding nuclei.
