Synchronized embryogenic cultures at different developmental stages were obtained by controlling 2,4-D concentration and developmental time.

通过对2，4-D浓度及生长发育时间的控制获得了高度同步化的各发育阶段体胚材料。

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"There was a lower concentration of dopamine markers in the brain of individuals with A.D.H.D., specifically in the areas of the brain that are involved with reward and motivation."

VOA: special.2009.09.29

Mr. MCWHORTER: I'd like to see a little more concentration on our own community, and then we'll get to Africa.

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This noise consisted mainly of the high-pitched whirr of the CPU fan, but it was barely noticeable -- to the point where if you got distracted, you'd have to re-focus your concentration just to make out the sound.

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The third major change is the concentration of activity in Washington, D.

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