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   89篇
  免费   0篇
  国内免费   18篇
系统科学   5篇
丛书文集   3篇
综合类   99篇
  2021年   1篇
  2020年   1篇
  2018年   13篇
  2017年   4篇
  2016年   1篇
  2015年   1篇
  2014年   1篇
  2013年   3篇
  2012年   20篇
  2011年   13篇
  2007年   1篇
  2005年   12篇
  2004年   2篇
  2003年   9篇
  2002年   5篇
  2001年   1篇
  2000年   1篇
  1999年   6篇
  1998年   6篇
  1997年   1篇
  1996年   1篇
  1995年   3篇
  1992年   1篇
排序方式: 共有107条查询结果,搜索用时 234 毫秒
101.
The outbreak of SARS sets an urgent task to reveal the origin of human SARS-CoV, i.e. its relation to other known species of coronavirus, and to trace the genetic variation in the spreading process of SARS. Partial answer to the problem may be obtained from phylogenetic analy-sis of available genomes. We call a phylogenetic tree of different species of coronavirus including the human SARS-Cov a CoV Tree and that of different isolates of SARS-CoV a SARS Tree. CoV trees have been c…  相似文献   
102.
在常用的计算时间阈值识别方法的基础上,提出了一种改进的基于 URL 页面类型、页面信息量和访问时间的平均阈值识别方法.针对不同的页面类型采用不同的阈值计算方法设置时间阈值,相对于已有的对所有用户页面使用单一的先验阈值和现有动态阈值计算,该方法能够更真实地反映用户会话的情况,且识别的准确率有了较大提高.  相似文献   
103.
The expression patterns of eight defense- related genes in the herbivore-infested and jasmonate- treated (jasmonic acid, JA and its derivative MeJA) rice leaves were analyzed using RT-PCR. The results showed that Spodoptera litura Fabricius (Lepidoptera: Noctuidae) herbi-vory induced the expression of lipoxygenase (LOX) and al-lene oxide synthase (AOS) genes that are involved in the jasmonate-signaling pathway. Moreover, S. litura damage resulted in the expression of farnesyl pyrophosphate syn-thase (FPS), Bowman-birk proteinase inhibitor (BBPI), phenylalanine ammonia-lyase (PAL) and other rice defense- related genes that were also induced by aqueous JA treat-ment or gaseous MeJA treatment. These indicated that in rice leaves, the JA-related signaling pathway was involved in the S. litura-induced chemical defense. Mechanical damage and brown planthopper (BPH), Nilaparvata lugens (St錶) (Homoptera: Delphacidae) damage induced the expression of LOX gene, but both treatments did not induce the expression of AOS gene. However, BPH damage induced the expression of acidic pathogen-related protein 1 (PR-1a), Chitinase (PR-3), and PAL genes, which is involved in the salicylate- signaling pathway. It was suggested that salicylate-related signaling pathway or other pathways, rather than jas-monate-signaling pathway was involved in the BPH-induced rice plant defense.  相似文献   
104.
Ionizing radiation (IR) causes severe cellular damage both directly and indirectly and disrupts RNA integrity. RNA strand breaks are the most frequent type of damage caused by IR. RNA damage is involved in the development of degenerative diseases, including Alzheimer’s disease and Parkinson’s disease. However, the mechanism of mRNA damage and any resulting pathophysiological outcomes are poorly understood. This is partly because there is a lack of sensitive tools to monitor damage randomly occurring in RNA,...  相似文献   
105.
Captive populations provide a precious genetic resource for endangered animals and a source of individuals for reintroduction to depleted habitats. Therefore, accuracy in determining paternity is of vital importance for managing captive populations and in selecting representative individuals of known genetic characteristics for release. In this study, we established a fast and effective method to conduct paternity testing for captive giant pandas in the Wolong population. This technique uses two highly poly...  相似文献   
106.
介绍了在室温下设计合成的一种功能化离子液体1,2-二甲基-3-丁基咪唑硫酸氢盐离子液体[mmBim][HSO4]均为在不同温度下测定了该离子液体的密度、表面张力、粘度和电导率等性质,并根据特定的经验方程,估算了该离子液体的热膨胀系数、标准熵和晶格能等性质参数,为该离子液体的预期应用提供了重要的数据参考.  相似文献   
107.
以1-甲酰基-2-甲氧基薁-3-甲酸甲酯为反应底物,通过与邻苯二胺缩合、烷基化、脱羧等过程,成功地制备了新型薁并[1,2-f]苯并[1,4]二氮卓类衍生物.反应收率良好、操作简单、条件温和.产物结构通过红外光谱、核磁共振谱、质谱及元素分析证实.  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