Very early risers and longtime night owls have a hard time ever changing, says David F. Dinges, chief of sleep and chronobiology at the University of Pennsylvania's Perelman School of Medicine.
宾夕法尼亚佩雷尔曼医学院睡眠和时间生物学主任大卫·丁格斯说，起得很早的人和长时间的夜猫子很难突然改变。
But the story of 1938 also shows how hard it is to apply these insights.Even under f.
但是，1938年的故事同时也告诉我们，要采用这些见解是多么的困难。
We choose to go to the moon and other things, not because they are easy, but because they are hard. —— John F. Kennedy.
我们选择去月球和其他的东西，而不是因为它们容易，而是因为他们是很难的。
"Pilots are most impressed by the minimal number of hard switches in the F-35 cockpit," he explains.
“飞行员们对于F - 35座舱内减少到最低限度的硬件开关留下了深刻印象，”他解释说。
F your photo is not online, click "Upload" and browse for the image on your computer's hard drive or connected device, such as a digital camera, USB card reader, or flash drive.
如果你的照片不是在线的，点击“上传”，然后从你的电脑硬盘或者连接设备如数码相机，读卡器以及闪存盘中浏览上传照片。
The results showed that the F-series composited brazed materials can be used efficiently to remove the residual stress within brazing join of hard alloy and steel.
实验指出，使用F系列银复合钎料，对消除上述材料焊缝的残余应力的效果明显。
The results showed that the F-series composited brazed materials can be used efficiently to remove the residual stress within brazing join of hard alloy and steel.
实验指出，使用F系列银复合钎料，对消除上述材料焊缝的残余应力的效果明显。
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