The phrase "all the existing studies" is correct and usable in written English.
You can use it when referring to the totality of studies that are currently available on a particular topic.
Example: "In order to draw a comprehensive conclusion, we must consider all the existing studies related to climate change."
Alternatives: "all current research" or "all available studies".
In all, the existing studies suggested that xylitol can reduce MS levels in saliva and plaque and reduce tooth decay.
12 We have systematically searched the literature and reviewed all the existing studies testing the association between bisphosphonates and esophageal or gastric cancer and performed a meta-analysis.
As a final comment, we need to acknowledge that all the existing studies operated in a policy context where no rewards or incentives existed to promote the use of patient decision support and were being done in parallel in a period where considerable resources were being invested in the adoption of electronic health care records.
All the existing studies on this topic have been focused on the longitudinally distributed mean concentration, far from enough to fully characterize the transport process with tremendous cross-sectional concentration nonuniformity.
Most of the errors were in documentation on matters in which all the existing studies point to no serious problem of siting design, or construction of the pipeline.
All the existing studies reconstructed ancestral states for male and female ornaments.
Almost all of the existing studies on product architecture adopt the research framework of comparing the advantages and disadvantages of modular architecture with those of integral architecture.
The simulation performance were all acceptable compared with the existing studies.
The existing studies all deal with TN associated with multiple sclerosis and are small open-label trials.
Our results extend almost all the related existing studies on the non-monotone time-delayed reaction-diffusion equations.
It was found that the simplified transition lines provide a good approximation of the regime transitions for all existing studies within the allowable range of the map.
