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   182篇
  免费   25篇
  国内免费   15篇
  2023年   3篇
  2022年   3篇
  2021年   10篇
  2020年   4篇
  2019年   3篇
  2018年   2篇
  2017年   2篇
  2016年   6篇
  2015年   9篇
  2014年   6篇
  2013年   8篇
  2012年   15篇
  2011年   12篇
  2010年   15篇
  2009年   14篇
  2008年   9篇
  2007年   12篇
  2006年   7篇
  2005年   11篇
  2004年   4篇
  2003年   9篇
  2002年   4篇
  2001年   4篇
  2000年   6篇
  1999年   5篇
  1998年   7篇
  1997年   4篇
  1996年   2篇
  1995年   2篇
  1994年   1篇
  1993年   2篇
  1989年   2篇
  1988年   2篇
  1987年   3篇
  1986年   2篇
  1985年   1篇
  1984年   1篇
  1982年   1篇
  1981年   1篇
  1978年   1篇
  1977年   4篇
  1976年   2篇
  1966年   1篇
排序方式: 共有222条查询结果,搜索用时 15 毫秒
91.

Background  

Zerumbone is a cytotoxic component isolated from Zingiber zerumbet Smith, a herbal plant which is also known as lempoyang. This new anticancer bioactive compound from Z. zerumbet was investigated for its activity and mechanism in human liver cancer cell lines.  相似文献   
92.
93.
This study explores diet differences between two populations of wild Bornean orangutans (Pongo pygmaeus wurmbii) to assess whether a signal of social learning can be detected in the observed patterns. The populations live in close proximity and in similar habitats but are separated by a river barrier that is impassable to orangutans in the study region. We found a 60% between‐site difference in diet at the level of plant food items (plant species–organ combinations). We also found that individuals at the same site were more likely to eat the same food items than expected by chance. These results suggest the presence of diet (food selection) traditions. Detailed tests of three predictions of three models of diet acquisition allowed us to reject a model based on exclusive social learning but could not clearly distinguish between the remaining two models: one positing individual exploration and learning of food item selection and the other one positing preferential social learning followed by individual fine tuning. We know that maturing orangutans acquire their initial diet through social learning and then supplement it by years of low‐level, individual sampling. We, therefore, conclude that the preferential social learning model produces the best fit to the geographic patterns observed in this study. However, the very same taxa that socially acquire their diets as infants and show evidence for innovation‐based traditions in the wild paradoxically may have diets that are not easily distinguished from those acquired exclusively through individual learning. Am J Phys Anthropol 143:175–187, 2010. © 2010 Wiley‐Liss, Inc.  相似文献   
94.
葡萄球菌是动物中重要的机会性病原体,耐甲氧西林金黄色葡萄球菌(MRSA)因其多药耐药的特征日益成为动物和公众健康的主要威胁。由于动物与动物及人畜间存在相互传染的风险,在控制MRSA感染的整个体系中,分析MRSA在动物中的流行显得尤为重要。  相似文献   
95.
Like many primates, orangutans face fluctuations in fruit availability. We show that in Ketambe (Sumatra), fruit availability fluctuations have very little influence on orangutan diet. Most importantly, the percentages of fruits including figs, fruits excluding figs, and figs in their diet do not differ significantly between periods of varying fruit availability. In addition, there is no trace of ketones in orangutan urine samples during periods of varying fruit availability. Unlike 1 orangutan population in Borneo, orangutans in Sumatra experience no prolonged negative energy budget because of fluctuations in fruit availability. Dietary data from other Sumatran and Bornean orangutan populations indicate that the pattern might be representative for a more general difference between Sumatra and Borneo, and we discuss how this might have affected orangutan reproduction and life history for the 2 species.  相似文献   
96.
We have used the in vitro selection method to search for catalytically active variants of the antigenomic delta ribozyme with mutations in the regions that constitute the ribozyme active site: L3, J1/4 and J4/2. In the initial combinatorial library 16 nt positions were randomized and the library contained a full representation of all possible sequences. Following ten cycles of selection-amplification several catalytically active ribozyme variants were identified. It turned out that one-third of the variants contained only single mutation G80U and their activity was similar to that of the wild-type ribozyme. Unexpectedly, in the next one-third of the variants the C76 residue, which was proposed to play a crucial role in the ribozyme cleavage mechanism, was mutated. In these variants, however, a cytosine residue was present in a neighboring position to the polynucleotide chain. It shows that the ribozyme catalytic core possesses substantial ‘structural plasticity’ and the capacity of functional adaptation. Four selected ribozyme variants were subjected to more detailed analysis. It turned out that the variants differed in their relative preferences towards Mg2+, Ca2+ and Mn2+ ions. Thus, the functional properties of the variants were dependent on both the structure of their catalytic sites and divalent metal ions performing catalysis.  相似文献   
97.
萨仁 《西北植物学报》2006,26(6):1256-1258
根据对标本的研究及文献资料的整理,证实了西伯利亚岩黄芪在中国的分布;山竹岩黄芪在新疆的分布新记录。另外,还报道了地中海岩黄芪在陕西的栽培记录。  相似文献   
98.
基于2001—2018年MODIS NDVI数据,采用累计归一化植被指数(NDVI)的Logistic曲线曲率极值法,识别内蒙古植被枯黄期及其时空变化特征,并在生态区尺度上分析枯黄期对气候因子和NDVI的响应特征。结果表明: 研究期间,内蒙古植被平均枯黄期主要集中在第260~280天。森林生态区枯黄期为第270~280天,从南向北推迟;草原生态区枯黄期最早,介于第257~273天,从东北向西南逐渐推迟;荒漠生态区枯黄期为第270~283天,东北向西南呈推迟态势。2001—2018年间,3个生态区植被枯黄期均呈不显著推迟趋势。植被生产力从东北向西南逐渐降低,在时间上呈增加趋势的面积大于呈减小趋势的面积。全内蒙古和各生态区植被枯黄期受季前2~3个月降水量的正面影响较大,与季前平均温度、最高温度和最低温度均呈正相关关系。全内蒙古和各生态区,8和9月植被生产力的增加(或减少)将推迟(或提前)植被枯黄期,而6和7月植被生产力的增加(或减少)将提前(或推迟)草原和荒漠生态区植被枯黄期。  相似文献   
99.
100.
单MYB转录因子成员RSM(RADIALIS-like SANT/MYB)突变,倒置黑暗诱导的叶绿素减少,原因有待确定;为了揭示RSM如何调控叶绿素积累,本研究运用基因工程途径,获得了普通烟草和马铃薯体内抑制和过量表达StRSM 1阳性转化株系,测定了阳性转化株系的叶绿素积累等生理表型;结果显示,普通烟草和马铃薯体内抑制RSM 1表达,显著增加了叶绿素积累,叶色随之加深;RSM 1过量表达,显著减少叶绿素积累,叶色变浅。叶绿素代谢相关基因表达测定结果显示,StRSM 1过量表达增加了黑暗下叶绿素结合蛋白CP24基因的表达,改变了其表达模式。以上结果表明,转录因子StRSM 1响应光照反向调控叶绿素积累,叶绿素结合蛋白CP24参与了StRSM 1对叶绿素积累的调控。结果有助于进一步明确RSM 1如何响应光照和深刻理解RSM 1参与的光照响应。  相似文献   
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