论文写作中，何时用主动语态，何时用被动语态？

主动语态-主语为行动的实施方。
被动语态-主语为行动的接收方。

在撰写科学论文时我们会使用各种各样的时态。下面是一些在不同时态下使用主动语态和被动语态的例子：

1.现在时-通常在概论，讨论和结论中使用的时态

Example 1:
Active: Vitamin A increases the risk of hair loss.
Passive: The risk of hair loss is increased by vitamin A.

Example 2:
Active: Volatile organic compounds (VOCs) emitted from industries and vehicle exhausts can induce a series of environmental problems, including photochemical smog, broken ozonosphere, and environmental pollution.

Passive: A series of environmental problems, including photochemical smog, broken ozonosphere, and environmental pollution, can be induced by volatile organic compounds (VOCs) emitted from industries and vehicle exhausts.

2.现在时-通常在目标中使用的时态

Example 1:
Active: In this study, we present our design of an electric hot water tank.
Passive: In this study, a design of an electric hot water tank is presented.

Example 2:
Active: This study develops an efficient methodology to examine a space–time continuous dataset for urban irrigation water use.
Passive: An efficient methodology to examine a space–time continuous dataset for urban irrigation water use is developed in this study.

3.现在完成时-通常在概论，讨论和总结中使用的时态

Example 1:
Active: Previous studies have used comparative analysis of ORF2 sequences to elucidate phylogenetic relationships among different FCV isolates.

Passive: Comparative analysis of ORF2 sequences has been used in previous studies to elucidate phylogenetic relationships among different FCV isolates.

Example 2:
Active: Only a small number of empirical studies have focused on the patterns and mechanisms behind disease clusters at small spatial scales, especially in wild host–pathogen systems [2].
Passive: The patterns and mechanisms behind disease clusters at small spatial scales, especially in wild host–pathogen systems, have been focused on by only a small number of empirical studies [2].

4.过去时：通常用于材料与方法/结果

Example 1:
Active: We determined the presence of larvae by dip netting.
Passive: The presence of larvae was determined by dip netting.

Example 2:
Active: We evaluated the number of haplotypes (h), haplotypes (Hd), and nucleotides (π) using the DnaSP 5.10 program [3].

Passive: The number of haplotypes (h), haplotypes (Hd), and nucleotides (π) was evaluated using the DnaSP 5.10 program [3].

Example 3:
Active: We found a strong correlation between above-ground and below-ground biomass accumulation in Platanus occidentalis.

Passive: A strong correlation was found between above-ground and below-ground biomass accumulation in Platanus occidentalis.