| Share | Phrase |
| 36.40% | heterocyclic [physical/chemical] compound |
| 26.99% | heterocyclic [physical/chemical] amine |
| 19.24% | heterocyclic [physical/chemical] group |
| 12.05% | heterocyclic [physical/chemical] monomer |
| 3.05% | heterocyclic [physical/chemical] structure |
| 2.24% | heterocyclic [physical/chemical] ring |