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We perform a next-to-leading order QCD analysis to world data on polarized structure functions $g_1$ and $g_2$ in fixed-flavor number scheme. We include target mass corrections and higher twist effects in our fitting procedure and study their non-negligible effects on physically interesting quantities. Twist-3 contributions to both polarized structure functions are determined and the accuracy of the extracted polarized parton distribution functions (PPDFs) is improved. $3^He$ and $3^H$ polarized structure functions are described based on our fit result. Moreover, sum rules are derived and compared with available theoretical and experimental results
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