The paper also puts forward opinions on the principles of the general survey of folk cultural l.

The general principle of phenomenological method in “returning back to real things themselves”;

The choice principle of chemistry activity-class content and its setting;

Introduced choice principle of parting surface and attentions in designing injection mold.

This paper introduces systemically the properties, the applications and the choice principle of welding materials used in long- distance transpon pipeline.

Attribute classification and selection principles of the evaluation indexes for science and technology journals;

The structure property, load distribution, selection principle, application scope and points for attention of cylindrical roller bearing used on surface-grinding machine were analyzed.

This paper briefly introduces the principles,components and classification of the leakage protector,and emphatically expounds the selection principles of the leakage protector,and puts forward some items needing attention in the erection and operation of the leakage protector.

The paper introduces classification of water supply pipe,and compares synthetic capacity of different pipe,discusses about choosing principles of pipe,proposes suggestion for pipe\'s selection.