Perhaps you should try some spelling variations:
thiet hach » thien hach, thuyet hach, thiet hai
hoc thiet » hoc thieu, hoc thuyet, hoc hien
canh manh » canh tranh, cach mang, van manh
lanh manh » lanh tranh, lan anh, van manh
nhung don » nhung van, nhung bo
dung cong » dung trong
san toan » van toan, dan toan, manh toan
toan cao » toan ban, toan tap

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: hoc thiet hach - ((canh manh) OR (lanh manh)) cua ((nhung don) OR (dung cong)) san toan cao~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "hoc thiet hach - ((canh manh) OR (lanh manh)) cua ((nhung don) or (dung cong)) san toan cao~".
• Adding a wildcard symbol may retrieve word variants: hoc thiet hach - ((canh manh) OR (lanh manh)) cua ((nhung don) or (dung cong)) san toan cao*.