Thanks for the reply. That's definitely right.
However, what I originally mean is sometimes I need to search for one English word within Chinese or Japanese but it cannot work. I understand that the English word would be a substring within a word. However I find when I search for a Chinese word within a pure Chinese sentence (also looks like a substring within a "word"), it works. Let me be specific.
Now the fact is that, for pure Chinese sentences, like
谢谢你的回复。
in which a word might be composed by one, two or several characters, and there is no space between two words, which means in English grammar we should make it
谢谢 你 的 回复。
(thanks for) (you) ('s) (reply.)
but we don't. When I search within it (I mean the first sentence 谢谢你的回复。) for one, two or several characters like 你, 回复 or sth else, the search results turn out to be right! In this case I guess 你 is also a substring within a string (word), but the search does work.
Secondly, when we want to use one English word within the Chinese sentence, we usually just put it in the sentence using the rule I've mentioned above, which means, no space between word and word, like
我喜欢Joplin这个软件。
What confuse me is that in this case when I search for Joplin it does not work. I understand in English environment the case is that I should search for Joplin within the sentence
I like the software called Joplin.
in which Joplin. is a word rather than a substring, and according to some rules we can throw away the dot and find Joplin.
It seems to me that there are two sets of rules for different languages and I wonder if there is any measure to search for Joplin within
我喜欢Joplin这个软件。
I hope I've made myself understood 
.
PS. For the example I mentioned last time, the fact is at* returns all items.
