To date, it remains unclear which search systems are most appropriate for evidence synthesis and why. Advice on which search engines and bibliographic databases to choose for systematic searches is limited and lacking systematic, empirical performance assessments.
Según este estudio, Google Scholar no es un buen buscador de artículos científicos:
Nevertheless, overall, Google Scholar's search precision has been found to be significantly lower than 1% for systematic searches [25]. This is not surprising, since our findings show that Google Scholar does not support many of the features required for systematic searches. Our findings support the criticism of Bramer et al [33], Bramer et al [34], and Boeker et al [25] and indicate that Google Scholar's coverage and recall is an inadequate reason to use it as principal search system in systematic searches [53]. If a system such as Google Scholar fails to deliver retrieval capabilities that allow a reviewer to search systematically with high levels of recall, precision, transparency, and reproducibility, its coverage is irrelevant for query-based search. Google Scholar's extraordinary coverage acting as a multidisciplinary compendium of scientific world knowledge should not blind users to the fact that users' ability to access this compendium is severely limited, especially in terms of a systematic search.
En Improving the Reliability of Literature Reviews: Detection of Retracted Articles through Academic Search Engines se puede leer:
In summary, no database provides 100% coverage of the scientific production in a specific area, which makes it necessary to use several of them in order to obtain greater coverage of the information retrieved.