Google Books search results and API results are different

Question

I'm currently using Google Books API(https://developers.google.com/books/docs/v1/using)

And It's weird that search results from the actual website or mobile app and search results from the API are different.

see my pic.

this is mobile app

this is website

and this is my query

https://www.googleapis.com/books/v1/volumes?q=r김란주&langRestrict=ko&maxResults=10&startIndex=0

I searched korean word "김란주".

What have I missed?

I tried query parameters. (https://developers.google.com/books/docs/v1/using#api_params)

But I didn't get the same result as the app or site.

And I found same situation. (The results of the Google books API and the website are different)

please help me. thx.