a helical content的用法和样例：
- Spirillum A helically shaped bacterium.
- The SARS viral nucleocapsid is tubular with a helical symmetry.
- A printer that forms dot matrix characters by means of linear, ridged print hammers that impact paper and ribbon against a helical ridge on a rotating cylinder.
- A helical buckling of pumping rods has taken place in the course of downstroke of pumping.
- A maxi- mum peak power of 660mW at 260.0nm was obtained with a helical hol- low cathode of 1.2m length, 6mm inner diameter and 9mm coil pitch.