Perhaps you should try some spelling variations:
"genotype variation method" » "genotypic variation method", "genome variation method", "phenotypic variation method", "genotype variational method", "genotype variational methods", "genotype evaluation method"
"genotype radiation method" » "genotypic variation method", "genotype evaluation method", "genotype modulation method", "genotype irradiation method", "genotype remediation methods", "genotype calibration method"
"isotope dilution method" » "isotope solution method", "isotope solution methods", "isotope evaluation method"

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (("isotope dilution method") or ((("genotype variation method") OR ("genotype radiation method"))))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("isotope dilution method") OR ((("genotype variation method") OR ("genotype radiation method")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"isotope dilution method\") or (((\"genotype variation method\") OR (\"genotype radiation method\"))))".
• Removing quotes may allow a broader search: (( isotope dilution method ) or ((( genotype variation method ) OR ( genotype radiation method )))).
• Adding a wildcard symbol may retrieve word variants: (("isotope dilution method") or ((("genotype variation method") OR ("genotype radiation method"))))*.