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   395篇
  免费   36篇
  2023年   3篇
  2022年   3篇
  2021年   8篇
  2019年   7篇
  2018年   9篇
  2017年   12篇
  2016年   13篇
  2015年   8篇
  2014年   8篇
  2013年   13篇
  2012年   18篇
  2011年   25篇
  2010年   14篇
  2009年   6篇
  2008年   15篇
  2007年   18篇
  2006年   19篇
  2005年   16篇
  2004年   13篇
  2003年   12篇
  2002年   10篇
  2001年   11篇
  2000年   26篇
  1999年   8篇
  1998年   6篇
  1997年   8篇
  1995年   3篇
  1992年   4篇
  1991年   9篇
  1990年   7篇
  1989年   10篇
  1988年   10篇
  1987年   3篇
  1986年   3篇
  1985年   5篇
  1984年   6篇
  1982年   3篇
  1979年   5篇
  1978年   7篇
  1977年   5篇
  1975年   4篇
  1974年   3篇
  1973年   3篇
  1972年   2篇
  1971年   2篇
  1970年   5篇
  1969年   2篇
  1968年   2篇
  1967年   2篇
  1966年   6篇
排序方式: 共有431条查询结果,搜索用时 15 毫秒
11.
Sampling properties of DNA sequence data in phylogenetic analysis   总被引:26,自引:6,他引:20  
We inferred phylogenetic trees from individual genes and random samples of nucleotides from the mitochondrial genomes of 10 vertebrates and compared the results to those obtained by analyzing the whole genomes. Individual genes are poor samples in that they infrequently lead to the whole-genome tree. A large number of nucleotide sites is needed to exactly determine the whole-genome tree. A relatively small number of sites, however, often results in a tree close to the whole-genome tree. We found that blocks of contiguous sites were less likely to lead to the whole-genome tree than samples composed of sites drawn individually from throughout the genome. Samples of contiguous sites are not representative of the entire genome, a condition that violates a basic assumption of the bootstrap method as it is applied in phylogenetic studies.   相似文献   
12.
13.
Systematic studies of the effectivity of aerosols of the mixtures of DDVP and pyrethroids tested on house flies revealed synergism among the mentioned substances the degree of which was determined by the composition of the mixtures. Among the formulae under study, the mixture of DDVP and neopynamin in a ratio 9 : 1 is of greatest interest.  相似文献   
14.
15.
16.
Seven cell lines transformed by adenovirus type 5 and its DNA were obtained. It was shown that different cell lines contain the fragments of viral DNA which differ in length and number of copies per DNA of diploid cells. They contain from the left end 6% of the viral DNA to complete or almost complete viral genome. All studied cell lines were sensitive to reinfection with adenovirus type 5. They produced no virus being cocultivated with cell sensitive to the virus. No cell line was able to induce tumors even in immunosuppressed newborn rats. All cell lines formed colonies in soft agar. The level of virus-specific antigens was higher in cells that contained a large part of the viral genome. The methods used did not allow to correlate the biological properties of the transformed cells with the length and the number of copies of the integrated part of the viral genome.  相似文献   
17.
18.
19.
Antonie van Leeuwenhoek - The diversity of anaerobic microorganisms in terrestrial mud volcanoes is largely unexplored. Here we report the isolation of a novel sulfate-reducing alkaliphilic...  相似文献   
20.
Water hyacinth Eichhornia crassipes is considered the most damaging aquatic weed in the world. However, few studies have quantified the impact of this weed economically and ecologically, and even fewer studies have quantified the benefits of its control. This paper focuses on water loss saving as the benefit derived from biological control of this plant between 1990 and 2013 at New Year’s Dam, Alicedale, Eastern Cape, South Africa. Estimates of water loss due to evapotranspiration from water hyacinth vary significantly; therefore, the study used three different rates, high, medium and low. A conservative raw agriculture value of R 0.26 per m3 was used to calculate the benefits derived by the water saved. The present benefit and cost values were determined using 10% and 5% discount rates. The benefit/cost ratio at the low evapotranspiration rate was less than one, implying that biological control was not economically viable but, at the higher evapotranspiration rates, the return justified the costs of biological control. However, at the marginal value product of water, the inclusion of the costs of damage to infrastructure, or the adverse effects of water hyacinth on biodiversity, would justify the use of biological control, even at the low transpiration rate.  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