Electrons on the outer surface of liquid helium form a nearly ideal two-dimensional electron system.

液氦外表面上的电子层构成一个近理想二维电子系统。

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However, more recent data imply that at least some parts of the planet did in fact experience long periods in the past during which liquid water existed on the surface.

然而，更新的数据表明，至少在该星球表面的一些部分的确存在过液态水，且存在于过去很长的一段时间内。

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Photographic evidence suggests that liquid water once existed in great quantity on the surface of Mars.

照片证据表明，液态水曾大量存在于火星表面。

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Or,they can be more complex such as using liquid glazes to change the color or shininess of the clay surface.

VOA: special.2009.09.09

Discovery of volcanic ice flows and melting of ice on the surface of Europa that support the premise of liquid oceans underneath.

CNN: Galileo moves on to Europa

In addition to containing the vast majority of the liquid freshwater on the surface of our planet, humans use lakes for more purposes than any other type of water system.

UNESCO: Summary

But, she says, it is still unclear if liquid on the surface of Titan is in the form of puddles, lakes or oceans although the arrival of a spacecraft called Cassini in 2004 might solve the mystery when it drops a probe into Titan's atmosphere.

ECONOMIST: Comparative meteorology