Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hieu van » hieu va, thien van, lieu va
nam thuc » nam thuoc, am thuc, nam thu
vu nang » vuc nang, va nang, vu dang
cao hoa » cao hoat, cao khoa, cau hoa
thuc xa » thuc xay, tuc xa, thuc va
xa hanh » xa thanh, xa khanh, va hanh

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((te sach) OR (toc sach)) vu nang cao hoa. hieu van nam thuc xa hanh ((dai cua) or (lai chau)) tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((te sach) OR (toc sach)) vu nang cao hoa. hieu van nam thuc xa hanh ((dai cua) OR (lai chau)) tre*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((te sach) OR (toc sach)) vu nang cao hoa. hieu van nam thuc xa hanh ((dai cua) or (lai chau)) tre*".