美国巴尔的摩马里兰大学的罗伯特·普鲁文斯和他的同事做过一项典型的研究。根据他的研究，笑是一件极其严肃的事情。
According to a classic study of laughter by Robert Provine of the University of Maryland, Baltimore County, and his colleagues, laughter is an unexpectedly serious business.
美国马里兰，巴尔的摩人体暴露PM 2.5和示踪元素。
Personal exposures to PM2.5 mass and trace elements in Baltimore, MD, USA.
美国马里兰，巴尔的摩人体暴露PM 2.5和示踪元素。
Personal exposures to PM2.5 mass and trace elements in Baltimore, MD, USA.
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