首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   6751篇
  免费   613篇
  国内免费   6篇
  2022年   57篇
  2021年   120篇
  2020年   82篇
  2019年   78篇
  2018年   110篇
  2017年   105篇
  2016年   163篇
  2015年   247篇
  2014年   264篇
  2013年   329篇
  2012年   445篇
  2011年   451篇
  2010年   298篇
  2009年   262篇
  2008年   374篇
  2007年   381篇
  2006年   327篇
  2005年   334篇
  2004年   301篇
  2003年   288篇
  2002年   282篇
  2001年   124篇
  2000年   138篇
  1999年   122篇
  1998年   92篇
  1997年   73篇
  1996年   67篇
  1995年   45篇
  1994年   54篇
  1993年   47篇
  1992年   73篇
  1991年   70篇
  1990年   80篇
  1989年   71篇
  1988年   49篇
  1987年   48篇
  1986年   46篇
  1985年   52篇
  1984年   36篇
  1983年   40篇
  1982年   47篇
  1981年   43篇
  1980年   41篇
  1979年   48篇
  1978年   39篇
  1977年   29篇
  1976年   29篇
  1975年   38篇
  1974年   31篇
  1973年   31篇
排序方式: 共有7370条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
Bird specimens collected by 19th century explorer and ornithologist Prince Maximilian of Wied-Neuwied form one of the foundation collections of the American Museum of Natural History in New York. However, parts of his collection remained in Germany and came to the Museum Wiesbaden. Since Wied described numerous new species without designating types, some of these specimens might be type material. Here we present a catalog of the 30 Wiesbaden specimens associated with him and discuss their potential type status. We conclude that 17 individuals in 11 species are potential type specimens that should be considered in future taxonomic work.  相似文献   
5.
6.
On the antennal tip of Eurypauropus ornatus are 3 threadlike sensilla—the flagella, and a single spheroid sensillum—the globulus. Each of the 3 flagella is innervated by 2 groups of sensory cells. One group contains 4 cells, the other, 5. All cells of the “four group” and 3 of the “five group” are comprised of single cilia and unbranched dendrites which extend along the lumen of the flagellum. Two cells of the “five group” have double cilia and pairs of unbranched dendrites. One pair also enters the flagellum and the other pair terminates beneath the flagellar base to form a concentric array of lamellae. No pores are present in the cuticular wall. Eight sensory cells innervate the globulus. They are arranged in 3 groups, one triplet and 2 pairs, in addition to a single cell. The single cell contains a pair of cilia whose unbranched dendrites differentiate into tubular bodies that are inserted into the base of the globulus. Each of the other 7 sensory cells has a single cilium. Their unbranched dendrites penetrate into the globulus in 3 groups as described for the sensory cells. The dendrites in each group terminate in an individual pore channel at the globulus tip and completely fuse with the electron-dense material that plugs the pore channel. Based on structural similarities to sensilla having known functions, it is probable that the flagella and the globulus are chemoreceptors, the former responding to odors, the latter sensitive to substances in aqueous solution.  相似文献   
7.
The ventral sebaceous gland of the Djungarian hamster is a macroscopically visible organ situated in the midventral area of the abdominal wall. It consists of densely packed acini arranged in lobules with common excretory ducts. The rich vascular network of the gland is characterized by fenestrated capillaries. Fenestrated endothelium has not yet been reported as a characteristic and regular finding within sebaceous glands. Results are discussed with regard to proliferation rate of sebocytes and the demand of fluid and nutrient supply.  相似文献   
8.
New World bats have recently been discovered to harbor influenza A virus (FLUAV)-related viruses, termed bat-associated influenza A-like viruses (batFLUAV). The internal proteins of batFLUAV are functional in mammalian cells. In contrast, no biological functionality could be demonstrated for the surface proteins, hemagglutinin (HA)-like (HAL) and neuraminidase (NA)-like (NAL), and these proteins need to be replaced by their human counterparts to allow spread of batFLUAV in human cells. Here, we employed rhabdoviral vectors to study the role of HAL and NAL in viral entry. Vectors pseudotyped with batFLUAV-HAL and -NAL were able to enter bat cells but not cells from other mammalian species. Host cell entry was mediated by HAL and was dependent on prior proteolytic activation of HAL and endosomal low pH. In contrast, sialic acids were dispensable for HAL-driven entry. Finally, the type II transmembrane serine protease TMPRSS2 was able to activate HAL for cell entry indicating that batFLUAV can utilize human proteases for HAL activation. Collectively, these results identify viral and cellular factors governing host cell entry driven by batFLUAV surface proteins. They suggest that the absence of a functional receptor precludes entry of batFLUAV into human cells while other prerequisites for entry, HAL activation and protonation, are met in target cells of human origin.  相似文献   
9.
10.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号