理论研究和实际应用之间存在时滞。
There is a time-lag between theoretical research and practical applications.
这是太阳能的最大缺陷——当太阳光变弱或者不存在时，人们该怎么解决。
That is the biggest drawback to solar energy, the problem of what do you do in cases where the sun's light is weak or virtually non-present.
当我尽我所能去想象一种永远令人向往或有吸引力的存在时，根本想象不出。总会变成一场噩梦。
When I do my best to imagine some kind of existence that would be desirable or attractive forever, it just doesn't work. It becomes a nightmare.
下一个块在备份目录不存在时创建该目录。
The next block creates the backup directory if it does not exist.
机遇存在时利用现有资产。
只有在文件存在时，-f操作符才返回true。
当这些选项存在时，最佳实践是转而关注于使用队列。
While these options exist, it is considered a best practice to instead concentrate on using queues.
当积压存在时，它们必须是需要的并可管理的。
当没有任何实现存在时，调用失败返回给父类。
When no implementation is present, the call falls through to the parent class.
我们说，当一个二元函数存在时，就有梯度向量。
So, we said when we have a function of two variables, we have the gradient vector.
只有当旧行为继续与旧值共同存在时，类型扩展才是安全的。
As long as the old behavior continues to exist with the old values, then type expansion is safe.
当你感觉有人威胁到你的存在时，你会反击以拯救自己。
When you feel that someone isthreatening your existence, you fight back to save yourself.
当你感觉有人威胁到你的存在时，你会反击以拯救自己。
When you feel that someone is threatening your existence, you fight back to save yourself.
当意识到这样的网站根本不存在时，他决定自己来建一个。
When he realized a site like that didn't exist, he decided to build it.
但是，也只有在保存古老语言与文化的愿望的确存在时，它才会有效。
But that will only work if the will to keep old languages and cultures alive really exists.
Soft和weak引用在引用不复存在时可被清除。
Soft and weak references can be cleaned up when they are no longer referenced.
当PI virtualizer存在时，使用这个VM参数。
在有大质量物体存在时，例如恒星，空间-时间会被扭曲或弯曲。
Space-time can be distorted or curved by the presence of massive objects, such as stars.
您需要管理这样的异常：每当所选的库不存在时就会抛出该异常。
You need to manage the exception that is thrown whenever the chosen library is not present. The example, then, has to be updated.
您已经看到了当 URL不存在时应该如何检查 404错误。
You've already seen how to check for a 404 error when a URL doesn't exist.
当设备可能不存在时，DSF特别有助于执行设备驱动程序内核代码。
DSF is especially helpful in executing device driver kernel code where the device may not be present.
当这些测量结合起来去确定代谢综合征的存在时，这种模式保持一样。
The pattern held when the measurements were combined to determine the presence of metabolic syndrome.
第二个方法接受一个布尔参数，这个参数用于判定会话不存在时是否创建新会话。
The second method accepts a boolean argument that determines whether or not a new Session will be created if it does not yet exist.
归根结底，正是我们对他人存在时的所感所受决定了我们自我茂盛的程度。
Ultimately it is how we feel in the presence of the other that will determine the degree to which we flourish.
不单单是惠伦怀疑一个充满活力的房地产市场不存在时美国经济将如何应对。
Mr Whalen is not alone in wondering how the American economy will cope without a buoyant property market.
他们还指出，当一种成熟的决策方法已经存在时，任何其他的方法都必须与其保持一致。
They also pointed out that mature design methods exist already and that any additional method must align with these.
而当我告诉三年级同学说圣诞老人是异教传统它并不存在时，就没人能够容忍了。
There was no tolerance when I told my third-grade class that Santa Claus was pagan and a lie.
反之当货币主义不再作为政策而存在时，通货膨胀目标被证明是比其更加有效的。
Whereas monetarism buckled as a policy, inflation targeting has proved far more effective.
反之当货币主义不再作为政策而存在时，通货膨胀目标被证明是比其更加有效的。
Whereas monetarism buckled as a policy, inflation targeting has proved far more effective.
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