Perhaps you should try some spelling variations:
dau tieng » dau tien, cau tieng, day tieng
hanh tai » thanh tai, hang tai, han tai
cac khoi » cac thoi, cac khoan, cach thoi
hieu van » hieu va, thien van, lieu va
tay lang » tai lang, tay tang, tay quang
van cam » van nam, van lam, van cau
cam duc » cam xuc, cao duc, pham duc
va hanh » van hanh, va thanh, va danh
ty lang » ty xang, ty hang, tu lang
cuu tre » cua tre, cau tren, cau treo
tu sach » thu sach, su sach, te sach

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 ((ty lang) OR (tay lang)) cac khoi. hieu van cam duc va hanh tai ((cuu tre) or (dau tieng))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ((ty lang) OR (tay lang)) cac khoi. hieu van cam duc va hanh tai ((cuu tre) OR (dau tieng)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ((ty lang) OR (tay lang)) cac khoi. hieu van cam duc va hanh tai ((cuu tre) or (dau tieng))".
• Adding a wildcard symbol may retrieve word variants: tu sach ((ty lang) OR (tay lang)) cac khoi. hieu van cam duc va hanh tai ((cuu tre) or (dau tieng))*.