Perhaps you should try some spelling variations:
tranh nghien » trinh nghien, tron nghien, trong nghien
tinh nghien » trinh nghien, kinh nghiem, tinh nghe
sach tranh » canh tranh
hanh tinh » hanh trinh, nhanh tinh, thanh tinh
nghien d » nghiem d, nghien o, nghiem de
tu hanh » du hanh, lu hanh, thuc hanh
so sach » so sanh, bo sach, co sach
de hoc » te hoc, dien hoc
du hoc » tu hoc, duoc hoc
d hoc » ad hoc, y hoc, _ hoc

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

• Performing a fuzzy search may retrieve terms with similar spellings: (( tu hanh tinh nghien ((de hoc) or (du hoc)) ) or ( so sach tranh nghien d hoc ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( tu hanh tinh nghien ((de hoc) OR (du hoc)) ) OR ( so sach tranh nghien d hoc )).
• Adding a wildcard symbol may retrieve word variants: (( tu hanh tinh nghien ((de hoc) or (du hoc)) ) or ( so sach tranh nghien d hoc ))*.