短语词组短语thermal asymmetric interlaced pcr 温度不对称pcrthermal asymmetric interlaced pcr tail -pcr 热不对称嵌套pcrtouchdown asymmetric PCR touchdown 不对称PCRasymmetric PCR hybridization 不对称PCR杂交asymmetric PCR -SSCP 不对称PCR 返回 asymmetric pcr