Perhaps you should try some spelling variations:
trinh thuc » trinh tu, trinh thi
canh trinh » canh tranh, hanh trinh, canh tinh
hanh khoa » hang khoa, anh khoa, hanh hoa
sach tri » sach tai, sach tren, sach truc
tri tham » thi tham, tri cham, tri tam
tham cac » thac cac, thoai cac, tham canh
cac khoa » cac khoan, cac khoi, dac khoa
khoa pho » khoa phu, khoa khoa, khoa phau
bo sach » co sach, hoc sach
khoa he » hoa he, khoa hoc, khong he
te canh » ve canh, te danh, re canh

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

• Performing a fuzzy search may retrieve terms with similar spellings: (( bo sach tri tham cac khoa he thong ) or ( te canh trinh thuc hanh khoa pho thong ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( bo sach tri tham cac khoa he thong ) OR ( te canh trinh thuc hanh khoa pho thong )).
• Adding a wildcard symbol may retrieve word variants: (( bo sach tri tham cac khoa he thong ) or ( te canh trinh thuc hanh khoa pho thong ))*.