妇女的平均月经周期是28天。
并非所有的医生都完全地了解生育周期。
进行周期性检查以确保高标准得以维持。
Periodic checks are taken to ensure that high standards are maintained.
这个周期一直循环往复。
每一种新产品都会有一个相对较长的使用周期。
我们必须避免类似20世纪80年代那样破坏性的繁荣-萧条周期。
We must avoid the damaging boom-bust cycles which characterized the 1980s.
更新周期的循环永远不会结束。
那么我的元素周期表是错的吗？
你知道太阳活动是有周期的。
这并不是说生物钟的周期是固定不变的。
This is not to suggest that the period of this biological clock is immutably fixed.
地球轨道的周期性变化会影响地球的气候。
Periodic changes in Earth's orbit could affect Earth's climate.
早期的元素周期表有空缺，缺少一些元素。
Early versions of the periodic table had gaps, missing elements.
他经历了周期性的变化。
这使人们确信天文周期已经存在了数十亿年。
It assures that the astronomical cycles have been in existence for billions of years.
这种周期性轨道只是彗星生命中的一个阶段。
This kind of periodic orbit is only a phase in a comet's life.
这能解释为什么它在元素周期表中缺失了吗？
正确的选择将消除沟通周期中可能出现的故障。
Proper selection will eliminate one source of likely breakdown in the communication cycle.
正确的选择将消除沟通周期中可能出现的故障。
Proper selection will eliminate one source of likely breakdown in the communication cycle.
鱼类的生命周期使其成为一种人类的基本食物。
Their life cycle helps man provide himself with a basic food—fish.
鼻翼两边的阻力呈现一种有规律的周期性变化。
There is a regular cycle of change in resistance between the two sides of the nose.
哈里森教授，你是在说周期表是可以预测的吗？
Professor Harrison, were you saying that the periodic table is predictive?
元素周期表的结构似乎限制了潜在元素的数量。
The structure of the periodic table appeared to limit the number of possible elements.
爸爸，我需要记住一个关于植物繁殖周期的单元。
Dad, I need to memorize a unit about the reproductive cycle of plants.
您可以根据工作和休息之间的周期来管理自己的能量。
You manage your energy in cycles that vary between work and rest.
地磁活动是地球磁场的自然变化，其波动周期为11年。
Geomagnetic activity, the natural variations in Earth's magnetic field, it fluctuates in 11-year cycles.
这些相同的变化周期对该区域稀少的人口产生了重大影响。
These same cycles of change had momentous impacts on the sparse human populations of the region.
如果雄蛙能够设法不经历这样的冻结周期就更可能交配成功。
If the male frog could manage not to go through this freezing cycle, he'd probably have more success in mating.
现在我们继续讨论，谈谈轨道，特别是那些所谓的周期轨道彗星。
Let's continue our discussion now by talking about orbits, especially those of the so-called periodic-orbit comets.
经济活动常常遵循周期性模式。
我签订的三年期合同已于上周期满。
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