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   137071篇
  免费   22898篇
  国内免费   9776篇
  2024年   169篇
  2023年   1347篇
  2022年   3187篇
  2021年   6141篇
  2020年   5793篇
  2019年   8163篇
  2018年   7989篇
  2017年   7103篇
  2016年   8535篇
  2015年   10664篇
  2014年   11632篇
  2013年   12512篇
  2012年   12151篇
  2011年   10800篇
  2010年   8663篇
  2009年   6871篇
  2008年   6715篇
  2007年   5699篇
  2006年   5010篇
  2005年   4026篇
  2004年   3499篇
  2003年   3229篇
  2002年   2796篇
  2001年   2315篇
  2000年   2005篇
  1999年   1944篇
  1998年   1123篇
  1997年   1084篇
  1996年   1023篇
  1995年   899篇
  1994年   855篇
  1993年   669篇
  1992年   869篇
  1991年   662篇
  1990年   504篇
  1989年   484篇
  1988年   377篇
  1987年   363篇
  1986年   283篇
  1985年   294篇
  1984年   167篇
  1983年   173篇
  1982年   112篇
  1981年   96篇
  1980年   66篇
  1979年   84篇
  1977年   63篇
  1975年   58篇
  1974年   54篇
  1973年   56篇
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
101.
A cDNA library was prepared from poly(A) mRNA extracted from 9-day hamster-yolk-sac erythroid cells. Two clones containing inserts coding for embryonic beta-like z or y globin-chains were isolated. Their identity was confirmed by (a) translation of hybrid selected mRNAs and (b) nucleotide sequence analysis of the inserts and comparison to the embryonic beta-like globin genes of Balb/c mouse. Availability of sequences for embryonic and adult globin cDNAs will aid in investigations of the molecular mechanisms of the globin switch in hamster YSEC.  相似文献   
102.
103.
104.
Ovarian cancer G protein-coupled receptor 1 (OGR1) is a proton-sensing molecule that can detect decreases in extracellular pH that occur during inflammation. Although OGR1 has been shown to have pro-inflammatory functions in various diseases, its role in autoimmunity has not been examined. We therefore sought to determine whether OGR1 has a role in the development of T cell autoimmunity by contrasting the development of experimental autoimmune encephalomyelitis between wild type and OGR1-knockout mice. OGR1-knockout mice showed a drastically attenuated clinical course of disease that was associated with a profound reduction in the expansion of myelin oligodendrocyte glycoprotein 35-55-reactive T helper 1 (Th1) and Th17 cells in the periphery and a reduced accumulation of Th1 and Th17 effectors in the central nervous system. We determined that these impaired T cell responses in OGR1-knockout mice associated with a reduced frequency and number of dendritic cells in draining lymph nodes during EAE and a higher production of nitric oxide by macrophages. Our studies suggest that OGR1 plays a key role in regulating T cell responses during autoimmunity.  相似文献   
105.
106.
107.
108.
Wing geometry helps to identify mosquito species, even cryptic ones. On the other hand, temperature has a well‐known effect on insect metric properties. Can such effects blur the taxonomic signal embedded in the wing? Two strains of Aedes albopictus (laboratory and field strain) were examined under three different rearing temperatures (26, 30 and 33 °C) using landmark‐ and outline‐based morphometric approaches. The wings of each experimental line were compared with Aedes aegypti. Both approaches indicated similar associations between wing size and temperature. For the laboratory strain, the wing size significantly decreased as the temperature increased. For the field strain, the largest wings were observed at the intermediate temperature. The two morphometric approaches describing shape showed different sensibilities to temperature. For both strains and sexes, the landmark‐based approach disclosed significant wing shape changes with temperature changes. The outline‐based approach showed lesser effects, detecting significant changes only in laboratory females and in field males. Despite the size and shape changes induced by temperature, the two strains of Ae. albopictus were always distinguished from Ae. aegypti. The present study confirms the lability of size. However, it also suggests that, despite environmentally‐induced variation, the architecture of the wing still provides a strong taxonomic signal.  相似文献   
109.
The human milk microbiome is vertically transmitted to offspring during the postnatal period and has emerged as a critical driver of infant immune and metabolic development. Despite this importance in humans, the milk microbiome of nonhuman primates remains largely unexplored. This dearth of comparative work precludes our ability to understand how species‐specific differences in the milk microbiome may differentially drive maternal effects and limits how translational models can be used to understand the role of vertically transmitted milk microbes in human development. Here, we present the first culture‐independent data on the milk microbiome of a nonhuman primate. We collected milk and matched fecal microbiome samples at early and late lactation from a cohort of captive lactating vervet monkeys (N = 15). We found that, similar to humans, the vervet monkey milk microbiome comprises a shared community of taxa that are universally present across individuals. However, unlike in humans, this shared community is dominated by the genera Lactobacillus, Bacteroides, and Prevotella. We also found that, in contrast to previous culture‐dependent studies in humans, the vervet milk microbiome exhibits greater alpha‐diversity than the gut microbiome across lactation. Finally, we did not find support for the translocation of microbes from the gut to the mammary gland within females (i.e., “entero‐mammary pathway”). Taken together, our results show that the vervet monkey milk microbiome is taxonomically diverse, distinct from the gut microbiome, and largely stable. These findings demonstrate that the milk microbiome is a unique substrate that may selectively favor the establishment and persistence of particular microbes across lactation and highlights the need for future experimental studies on the origin of microbes in milk.  相似文献   
110.
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