Over the years, waves of farmers have surged into the towns and cities, some seasonally, some for an extended period of time.

多年以来，一波又一波的农民拥入城镇，有些是季节性的，有些是持续一段时间的。

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But on soft soils, vibrations from long-period seismic waves are amplified, possibly exacerbating the swaying of skyscrapers.

但是，在松软的土层上，长周期地震波的震动会被放大，可能使摩天大楼的摇摆更加剧烈。

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Adjust the exciting period, learning a wave of high waves.

调节好兴奋期，学习一浪高一浪。

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The hydraulic compression of the waves compressed me over a period of three seconds until I heard three bones fracturing in my shoulders.

FORBES: Larry Ellison

The period of the chop is shorter, since waves have less room to build than they do at sea.

FORBES: Windy City Sailing

The Pew Center conducted two waves of polling over a seven-day period between September 8 and Tuesday.

CNN: Latest presidential polls vary widely