Gear drawing standards - part 1: for spur, helical, doublehelical and rack.
齿轮制图标准。第1部分：正齿。螺旋齿。双螺旋齿和齿条。
2
When carries various chemical modifications on doublehelical molecular of optically active, we can always gain derivatives which have specific properties.
在具有光学活性的螺旋分子母体上进行各种化学修饰，可以获得许多具有特殊性能的衍生物。
3
Objective To evaluate the clinical value of doublehelical ct angiography (DHCTA) and coronary artery calcification (CAC) detection in diagnosis of coronary heart disease (CHD).