首页 | 官方网站   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   96886篇
  免费   20427篇
  国内免费   5652篇
生物科学   122965篇
  2024年   101篇
  2023年   856篇
  2022年   1438篇
  2021年   4059篇
  2020年   4422篇
  2019年   6432篇
  2018年   6378篇
  2017年   6039篇
  2016年   6931篇
  2015年   8276篇
  2014年   8851篇
  2013年   9366篇
  2012年   8268篇
  2011年   7431篇
  2010年   6552篇
  2009年   5001篇
  2008年   4361篇
  2007年   3668篇
  2006年   3200篇
  2005年   2769篇
  2004年   2336篇
  2003年   2188篇
  2002年   1792篇
  2001年   1524篇
  2000年   1453篇
  1999年   1284篇
  1998年   673篇
  1997年   612篇
  1996年   639篇
  1995年   545篇
  1994年   556篇
  1993年   416篇
  1992年   606篇
  1991年   477篇
  1990年   410篇
  1989年   364篇
  1988年   296篇
  1987年   291篇
  1986年   264篇
  1985年   252篇
  1984年   174篇
  1983年   172篇
  1982年   135篇
  1981年   82篇
  1980年   89篇
  1979年   117篇
  1978年   84篇
  1977年   84篇
  1976年   82篇
  1974年   101篇
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
91.
92.
93.
94.
95.
96.
97.
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   
98.
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   
99.
C. P. W. Warren  K. S. Tse 《CMAJ》1974,110(4):425-427,429
Using a solid-phase radioimmunoassay, serum IgE level was determined in 46 normal subjects, 53 patients with bronchial asthma, 44 patients with chronic bronchitis and / or emphysema, and 19 patients with restrictive lung disease. Sputum IgE was measured simultaneously in 51 of the subjects. The range of serum IgE concentration in the normal subjects was wide. It varied between 15 and 750 ng/ml with a mean of 135 ng. Asthmatic patients had significantly higher levels of serum IgE with a mean of 579 ng/ml, but only 30% fell outside the normal 95% confidence limits. Patients with chronic bronchitis, emphysema and restrictive lung diseases had normal IgE levels. There was a significant correlation between serum and sputum IgE levels.  相似文献   
100.
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-23

京公网安备 11010802026262号