如果组合键是标准，那么就不可能很快发生变化。

If composite keys are the standard, then that's not likely to change any time soon.

youdao

这样的重复是创建组合键所必需的。

This duplication is required to create the composite key.

youdao

某些时候使用组合键的原因是所选键在某些方面与最终用户的业务领域相关联。

Composite keys are sometimes used because the choice of key relates in some way to the end-user business domain.

youdao

And the last bond that we have here is a carbon-carbon bond, and this is our last p orbitals that are coming together.

最后一个键是碳碳键，这是最后一个组合的p轨道。

麻省理工公开课 - 化学原理课程节选

There's not two bonds, that's one pi bond, and the reason is because it's 2 p orbitals coming together, and remember p orbitals have electron density above and below the axis, so when they come together, it kind of looks like one bonds, but essentially what we have here is one pi bond.

这不是两个键，这是一个π键，因为这是两个2p轨道组合而成的，记住p轨道在键轴之上,和键轴之下都有电子密度，当它们靠近时，这看着很像两个键，但本质上它是一个π键。

麻省理工公开课 - 化学原理课程节选