'substantial fluctuations' is correct and usable in written English.
You can use it to describe a situation where there are large, noticeable changes in a particular measurement. For example: Over the past year, the stock market has seen substantial fluctuations in value.
However in July, ionosonde measurements indicate substantial fluctuations with several peaks with magnitude consistently and radically than the IRI ones.
However, this overall share has contained substantial fluctuations between day and night and also fluctuations dependent on the availability of wind and sun [8].
On the other hand, substantial fluctuations in wine composition may require adjustments of operational conditions or the use of specific control loops to prevent an off-specification product.
The results presented here reveal that AR 6 most readily detaches/unfolds from the AR domain, undergoing substantial fluctuations at room temperature.
Shallow lakes in a continental, low Arctic setting are found to undergo substantial fluctuations in heavy-isotope content during the annual cycle due to extreme seasonality in water balance processes.
The design and operation of power plants that use waste, thermally exploitable waste products and biomass as fuels are considered difficult because there are substantial fluctuations in the fuel composition and the resulting energy content.
What's more, the abundance of many circRNAs exhibited substantial fluctuation in response to synaptogenesis, consistent with the idea that circRNAs might regulate synaptic function during development (You et al., 2015).
The plot shows substantial fluctuation in both the AA and CG simulations.
To avoid substantial fluctuation in the blood concentrations of cyclosporine, it has to be administered by continuous intravenous infusion.
It is obvious that residues of Apo protein from 70 to 100 exhibit substantial fluctuation, but the three candidates remain stable.
Data examined on adults also show substantial fluctuation, varying from 3 days (range = 2-6 days) to 14 ± 8 days [ 22, 24].
