Perhaps you should try some spelling variations:
"doc canh tranh tren" » "doc canh trinh tren", "doc canh tran tren", "doc canh tranh trong", "doc hanh tranh tren", "do canh tranh tren", "doi canh tranh tren"
"thuoc sach dinh tren" » "hoc sach dinh tren", "nuoc sach dinh tren", "thuat sach dinh tren", "thuoc sach kinh tren", "thuoc hoach dinh tren", "thuoc xac dinh tren", "thuoc sach dinh trong", "thuoc sach dinh tri", "thuoc sach dinh dien"
"tu sach danh tren" » "tu sach tranh tren", "tu sach dao tren", "tu sach dung tren", "tu sach doanh tren", "tu sach dan tren", "tu sach lanh tren", "thu sach danh tren", "su sach danh tren", "te sach danh tren"

Try widening your search to All Fields.

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (("tu sach danh tren") or ((("thuoc sach dinh tren") or ("doc canh tranh tren"))))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("tu sach danh tren") OR ((("thuoc sach dinh tren") OR ("doc canh tranh tren")))).
• Removing quotes may allow a broader search: (( tu sach danh tren ) or ((( thuoc sach dinh tren ) or ( doc canh tranh tren )))).
• Adding a wildcard symbol may retrieve word variants: (("tu sach danh tren") or ((("thuoc sach dinh tren") or ("doc canh tranh tren"))))*.