Not a DOI

The resolution service at https://doi.org resolves DOIs. You have attempted to resolve core/services/aop-cambridge-core/content/view/43819B490B72F072154DBDEAFE9807E8/S0007125000172125a.pdf/cross-national-prevalence-and-correlates-of-adult-attention-deficit-hyperactivity-disorder.pdf, which is not a DOI.

core/services/aop-cambridge-core/content/view/43819B490B72F072154DBDEAFE9807E8/S0007125000172125a.pdf/cross-national-prevalence-and-correlates-of-adult-attention-deficit-hyperactivity-disorder.pdf may be a Handle (DOIs are a special sort of Handle). If core/services/aop-cambridge-core/content/view/43819B490B72F072154DBDEAFE9807E8/S0007125000172125a.pdf/cross-national-prevalence-and-correlates-of-adult-attention-deficit-hyperactivity-disorder.pdf is a valid Handle you should be able to resolve it at https://hdl.handle.net.