罗伯特·威尔基Robert Leon Wilkie Jr. (born August 2, 1962) is an American lawyer and government official serving as the United States Secretary of Veterans Affairs. He was co
贝切定律贝切定律(英文;Birch's law),是美国地球物理学家弗朗西斯·贝切(英语:Francis Birch (geophysicist))于1961年建立的,指出在平均原子量为 M