Hello,
I tried to search a document with a sub-word but failed.
Does DT always require full word?
For example, Instead of searching with ‘google’, can i use ‘goo’ to find documents containing ‘google’?
Until now, the result is negative.
Wildcards work only for document Names.
But you can use the Phrase operator. I would suggest using “goog” instead of “goo” in order to avoid results that include “good”, “lagoon” and so forth. “Googl” might be still better to filter results.
The fractions of a second for typing an extra letter or two can save a lot of time while examining search results. 
Thank you for your reply.
At the first time, I didn’t understand what you mean by “phrase” search.
But, I tried to click the “magnifier” icon beside the text box to input the search keyword, everything is solved. (A drop-down menu was pulled out and it was the key to change the search method.)
Now, I can get the result I wanted. Thanks again.
- Jerome
I always use the Search window (Tools > Search), because I can see at a glance all of the search settings, and because it can be much more powerful in use.
This is also the window that will open if you select a text string and use the Lookup command (Command-Slash). A new Search window opens with the selected text already entered in the query field.
The Search window is more powerful than the search field in view windows, as it provides a number of additional options. This is the one to use if you wish to search a specific group, search for State, Label or Lock characteristics, or quickly vary your query conditions, etc.
So if you wish to learn all the tricks available in DEVONthink searches, I suggest using the Search window.