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Yun Qian*, Yudi Lin, Tiemei Zhang, Jianling Bai, Feng Chen, Yi Zhang, Senlin Luo and Hongbing Shen
* Corresponding author: Yun Qian dr_yunqian@yahoo.cn
BMC Public Health 2010, 10:139 doi:10.1186/1471-2458-10-139
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