英语中气体名词前用不用加the

不能这样不分具体情况就说的啦.
Where is the oxygen you bought yesterday? 不就有the?
the oxygen in this bottle不就一定得加the?
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Bertrandsky 说：
“但当气体名词修饰名词时,可以使用定冠词the
如：the nitrogen cycle ——氮循环；
the element nitrogen —— 氮元素”
两例中的 the 与气体 nitrogen 没有关系了!
在"the nitrogen cycle"中,短语中心是 the cycle,nitrogen 作定语.用了 the 不是因为有 nitrogen.我们不能说,在 the tall tree 中用了the 是因为有了 tall (作定语).在 the university student 中用了 the 也不是因为有university.
在the element nitrogen 中,更是另外一回事啦. nitrogen 作的是the element 的同位语.the 与nitrogen 没直接关系.
例子：The word vis-a-vis is from French. (vis-a-vis 这个词来自法语.)
The sentence "Long time no see" is calqued from Chinese.

Bertrandsky 还说：
“楼上(指ylyuan68)说的the oxygen 大概是指 the oxygen bottle/tank等,省略‘容器’名词
而the oxygen in this bottle,此处特指瓶装的氧气可以加定冠词”
------------这这这这这.解释.
Where is the oxygen you bought yesterday?
怎么也不可能等于：
Where is the oxygen bottle/tank you bought yesterday?
Where is the oxygen you bought yesterday?
倒是极可能等于：
Where is the bottled oxygen you bought yesterday?
(说极有可能,只是因为也有可能是罐装的或袋装的--我是外行,不知是否有袋装的氧气.不管怎么说,the bottled oxygen (瓶/罐装的氧气) 与 the oxygen bottle (氧气瓶/罐)已经是云泥之别了.)
在 "Where is the oxygen you bought yesterday?”中用 the 就是一简单特指,特指昨天买的氧气,与是瓶是罐的没关系.与The apples I bought yesterday were eaten by the squirrels. 中 apple 前面的 the 的用法毫无二致.
在 "the oxygen in the bottle"中,之所以说/写成 the oxygen 仅仅是因为特指瓶中的氧气.
the oxygen you bought yesterday
the oxygen in the bottle
都是因为特指,才在oxygen 前加了the.没有别的原因.
道理是这样的：一般来说,物质名词表抽象概念即为不特指,而不特指就不加 the,所以要说成 lack of oxygen (缺氧).lack of the oxygen (表缺特定的氧---岂不怪哉?)
I know the use of the definite article "the" is very confusing, and to many it is a mission impossible. What is more discouraging is grammatical theory does not really help that much. And oftentimes theoretical explanation could make things more complex and frustrating. It is my personal experience that language intuition is the most helpful, and this intuition could most effectively be developed by reading extensively. Don't let yourselves be boggled down by grammar proper. Remember "English is crazy." When you have learned 500 grammatical rules, you will run into an equal number of exceptions, or perhaps even more. And don't be surprised. This is what English is like. CRAZY. I'm going to drop this topic and I don't want to come back. Enjoy your study of "the".