There are two criteria by which a successful search may be judged:
retrieving what you need
retrieving all you need
Precision and recall are inversely proportional. A highly precise search will find few items (low recall) but most, if not all, of the results will be exactly what you need. A search designed for high recall will retrieve much more of what you need but will also include more material that you do not (low precision).
A literature review requires high recall results - that need for thoroughness involves more time, effort and different search strategies than the simple type of keyword searching used for precision.
Can you describe your information need using one simple sentence or question?
Without a clear idea of the project, you may not be able to determine which are the best resources to search, what terminology should be used in those resources, and if the results are appropriate and sufficient.
If you're having difficulty getting your project described succinctly, try using a PICO chart to identify the concepts involved:
For a compressor cascade (P), what is the influence of free stream turbulence (I) on air flow (O)?
Can molecular modeling (I) be more cost effective (O) than lump modeling (C) for heavy oil refining (P)?
Is solar-power (I) feasible (O) for running residential air-conditioning in desert climates (P)?
Searching within a resource is always a multi-part process:
A. Start with a P AND I search
B. Expand the P AND I search to include synonyms
C. Search using the database's controlled vocabulary for P AND I
D. Where do the C (comparison) and O (outcome) come into the search strategy?
E. For the most important documents you found, use citation searching to find even more:
Scientists would rather share each other's underwear than use each other's nomenclature