Perhaps you should try some spelling variations:
trinh thiet » trinh viet, trinh thi
hanh trinh » canh tranh, hanh chinh
sach trinh » sach kinh, sach tren, sac tinh
sach tranh » canh tranh
nghien dau » nghiem dau, nghiep dau, nghien cuu
thiet de » thiet ke, nhiet de, thiet yeu
ly hanh » ly anh, ly hang, lu hanh
dau hoc » dai hoc, du hoc, dan hoc
de hoc » te hoc, du hoc, dien hoc

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

• If you are trying to use Boolean operators, they must be ALL CAPS: (( ly hanh trinh thiet de hoc ) OR ( thu ((sach trinh) OR (sach tranh)) nghien dau hoc ))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( ly hanh trinh thiet de hoc ) or ( thu ((sach trinh) OR (sach tranh)) nghien dau hoc ))~".
• Adding a wildcard symbol may retrieve word variants: (( ly hanh trinh thiet de hoc ) or ( thu ((sach trinh) OR (sach tranh)) nghien dau hoc ))*.