缓慢的、持续的变化可能是环境稳定时期的常态，而新物种的快速进化发生在环境压力时期。
Slow, continuous change may be the norm during periods of environmental stability, while rapid evolution of new species occurs during periods of environment stress.
也可以在特定时期内调用该工具一定的次数，帮助您了解随着时间的变化数据库中的变动情况。
The utility can also be invoked a specified number of times within a specified period of time, to help you understand changes over time.
在一定时间范围内，科学家们已经可以准切的指出该地区每周的天气变化，而这也是到目前为止测绘出的最精确的气象历史。
In some stretches, the scientists were able to pinpoint what the region's weather was like from one week to the next — by far the most detailed climate history ever produced.
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