a tough nut

n.

难对付的人， 与之打交道有危险的人；

A Tough Nut
A Tough Nut
A Tough Nut
The coccidian oocyst: a tough nut to crack!
A Hard Nut to Crack: The Protection of Technological Measures
The lymph follicle: a hard nut to crack
Introduction to the special issue on multiword expressions: Having a crack at a hard nut
Speciation of Se in Bertholletia excelsa (Brazil nut): a hard nut to crack?
Work-ability evaluation: A piece of cake or a hard nut to crack?
A Tough Nut for Proof Procedures
Why patient safety is such a tough nut to crack.
The Chlamydial Type III Secretion Mechanism: Revealing Cracks in a Tough Nut
Nutrition: a hard nut to crack. An exploration of the knowledge, attitudes and activities of qualified nurses in relation to nutriti...