您可以使用波浪号（~）来放置下标，使用插入符号（^）来放置上标;然后使用sprintf来获得预期的数字格式：

---
title: "Table won't work"
author: "Exhausted student"
date: "2022/01/28"
output: 
  bookdown::word_document2
---

```{r table, echo=F, warning=F, message=F}
library(tidyverse)

expSup <- function(x, digits=3) {
  sprintf(paste0("%05.", digits, "f x 10^%d^"), x/10^floor(log10(abs(x))), floor(log10(abs(x))))
}

a <- tibble(
  constants = c("c", "N~A~", "h", "e", "H~2~0"),
  values = expSup(c(2.998e8, 6.022e-23, 6.626e-34, -1.602e-19, 18.02))
)

knitr::kable(a)

![](https://i.stack.imgur.com/mnpjw.png)

对于此open issue，一个选项可能福尔斯禁区：
1.创建html文档
1.为下标插入html标记
1.打开html文件（不是查看器）

1. ctrl+c，然后在你的word文件中ctrl+v。

---
output: html_document
---

```{r table, echo=F, warning=F, message=F}
library(tidyverse)
library(gt)
a <- tibble(
    constants = c("c", "N<sub>A</sub>", "h","e","H<sub>2</sub>O"),
    values = c(2.998e8, 6.022e23, 6.626e-34, -1.602e-19, 18.02)
)
a %>%
  mutate(constants = map(constants, html)) %>%
  gt() %>%
  fmt_scientific(values)

Maël's answer中的expSup()函数将科学格式转换为markdown格式。对于我的脚本，我稍微修改了一下函数：

exp_sup <- function(x, digits = 3) {
  sprintf(paste0("%05.", digits, "f $\\times$ 10^%d^"), x / 10^floor(log10(abs(x))), floor(log10(abs(x))))
}

我将"f x 10^%d^"更改为"f $\\times$ 10^%d^"，以便显示正确的乘法符号（×）。

使用flextable

这种格式在Kable中运行良好。但是，我的大部分工作流需要flextable来制作标题/交叉引用/出版样式/等等。不幸的是，尽管expSup函数自动将科学符号格式化为markdown，但它不能使markdown语法在flextable中运行。
然而，ftExtra::colformat_md()可以。因此，通过将修改后的exp_sup()函数与ftExtra组合，我最终能够生成一个学术外观的表：

下面是我最终输出的代码;如果您也试图制作可重复的学术报告与大量的表格在Word格式，希望这有帮助！

---
title: "The tables work!"
author: "Satisfied Student"
date: "2022/01/28"
output: 
  bookdown::word_document2:
    reference_docx: styleRef.docx
---
```{r setup, include = F}
library(easypackages)
packages(
  "tidyverse",
  "flextable", # This works best for my workflow
  "ftExtra", # For markdown formatting work in flextable
  "officer" # You can customize appearance/format/etc. of caption *prefixes*
)

knitr::opts_chunk$set(
  warning = FALSE,
  message = FALSE,
  echo = FALSE,

  # Make the table caption format definable in reference_docx styles
  tab.cap.style = "Table Caption",

  # Make "Table 1:" prefixes not bold
  tab.cap.fp_text = fp_text_lite(bold = FALSE)

  # The tab.cap settings MUST be in a separate chunk from tables
)

# Converts scientific format to markdown
exp_sup <- function(x, digits = 3) {
  sprintf(paste0("%05.", digits, "f $\\times$ 10^%d^"), x / 10^floor(log10(abs(x))), floor(log10(abs(x))))
}
# The $\\times$ makes proper multiply symbols

a <- tibble(
  constants = c("c", "N~A~", "h", "e", "H~2~O"),
  values = c(2.998e8, 6.022e23, 6.626e-34, -1.602e-19, 18.02)
)

a %>%
  mutate(values = exp_sup(values)) %>%
  flextable() %>%
  set_caption(
    caption = "(ref:foo)", # Produces formatted caption text
    style = "Table Caption"
  ) %>%
  colformat_md() %>% # Subscript/superscript works in flextable now!
  theme_booktabs() %>% # The 3-part-table used in academics
  align(align = "center", part = "all") %>% #Align everything to center
  set_table_properties(layout = "autofit") # Comfortable width/height every cell

(ref:foo) A scientifically formatted flextable with ^superscripts^ and ~subscripts~

## 更新：在表标题中使用markdown

以前我使用文本引用（例如`(ref:foo)`）在表格标题中使用markdown格式。现在似乎无法正确渲染。（截至2023年4月。不知道是哪个包导致的）
要解决这个问题，您可以将markdown标题写为字符串，然后将其传递给`set_caption()`中的`ftExtra::as_paragraph_md()`。例如：

tab_caption <- "A scientifically formatted flextable with ^superscripts^ and ~subscripts~"

a %>%
flextable() %>%
set_caption(
caption = ftExtra::as_paragraph_md(tab_caption), # <- Here
style = "Table Caption"
) %>%
colformat_md() %>%
theme_apa() %>% # The 3-part-table used in academics
align(align = "center", part = "all") %>%
set_table_properties(layout = "autofit")

您的代码应如下所示：

{r table, echo=F, warning=F, message=F}
library(tidyverse)
a <- tibble(
constants = c("c", "NA", "h", "e", "$H_2O$"),
values = c("$2.998 * {10^{8}}$", "$6.022 * {10^{-23}}$", "$6.626 * {10^{-34}}$", "$-1.602 * {10 ^{-19}}$", "$1.802 * {10^{1}}$")
)

knitr::kable(format = "html", a, digits = 35)

它会给予你这样的输出：