Perhaps you should try some spelling variations:
dua tren » dung tren
dang nam » dong nam, dan nam, dung nam
hanh tai » thanh tai, hang tai, han tai
cho hoc » co hoc, khoa hoc
cuu tre » cua tre, cau tren, cau treo
va hanh » van hanh, va thanh, va danh
tu sach » thu sach, su sach, te sach
hieu va » lieu va, hieu qua
nam hoi » nam khoa
y dang » ky dang, 2 dang, _ dang

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 y dang nam hoi. hieu va ((chon loc) OR (cho hoc)) va hanh tai ((cuu tre) or (dua tren))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach y dang nam hoi. hieu va ((chon loc) OR (cho hoc)) va hanh tai ((cuu tre) OR (dua tren)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach y dang nam hoi. hieu va ((chon loc) OR (cho hoc)) va hanh tai ((cuu tre) or (dua tren))".
• Adding a wildcard symbol may retrieve word variants: tu sach y dang nam hoi. hieu va ((chon loc) OR (cho hoc)) va hanh tai ((cuu tre) or (dua tren))*.