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   517篇
  免费   27篇
  544篇
  2024年   6篇
  2022年   4篇
  2021年   6篇
  2020年   5篇
  2019年   4篇
  2018年   10篇
  2017年   5篇
  2016年   12篇
  2015年   23篇
  2014年   19篇
  2013年   35篇
  2012年   37篇
  2011年   31篇
  2010年   26篇
  2009年   26篇
  2008年   24篇
  2007年   27篇
  2006年   18篇
  2005年   11篇
  2004年   20篇
  2003年   18篇
  2002年   13篇
  2001年   13篇
  2000年   12篇
  1999年   11篇
  1998年   9篇
  1997年   4篇
  1996年   3篇
  1993年   5篇
  1992年   9篇
  1991年   9篇
  1990年   8篇
  1989年   3篇
  1988年   5篇
  1987年   6篇
  1986年   4篇
  1985年   6篇
  1984年   4篇
  1983年   3篇
  1982年   4篇
  1976年   5篇
  1975年   2篇
  1974年   2篇
  1973年   3篇
  1970年   2篇
  1969年   2篇
  1967年   3篇
  1966年   2篇
  1962年   2篇
  1938年   2篇
排序方式: 共有544条查询结果,搜索用时 0 毫秒
1.
2.
A series of novel 1,7-disubstituted oxyindoles were shown to be potent and selective EP3 receptor antagonists. Variation of substitution pattern at the C-3 position of indole enhanced in vitro metabolic stability of the resulting derivatives. Series 27a–c showed >1000-fold selectivity over a panel of prostanoid receptors including IP, FP, EP1, EP2 and EP4. These agents also featured low CYP inhibition and good activity in the functional rat platelet aggregation assay.  相似文献   
3.
Chromatin immunoprecipitation (ChIP) assays allow the efficient characterization of the in vivo occupancy of genomic regions by DNA-binding proteins and thus facilitate the prediction of cis-regulatory sequences in silico and guide their validation in vivo. For these reasons, these assays and their permutations (e.g., ChIP-on-chip and ChIP-sequencing) are currently being extended to several non-mainstream model organisms, as the availability of specific antibodies increases. Here, we describe the development of a polyclonal antibody against the Brachyury protein of the marine invertebrate chordate Ciona intestinalis and provide a detailed ChIP protocol that should be easily adaptable to other marine organisms.  相似文献   
4.
1. A cactus, Opuntia stricta , has invaded almost 16 000 ha of conserved, natural habitatand has become a major weed problem in Kruger National Park (KNP), South Africa.
2. The main objectives in the control of O. stricta are to reduce the density of the weed and to curb long-range dispersal of seeds by preventing young plants from reaching the size (28 cladodes) at which they start to produce fruits.
3. Herbicides have failed to provide satisfactory control of O. stricta because the weed infestations are replenished from seeds in the soil and from small plants that are overlooked during spraying.
4. A phycitid moth, Cactoblastis cactorum , was released in KNP during 1988 in an attempt to control O. stricta biologically.
5. Population counts of the biological control agent and of the weed over a 5-year period showed that, even though C. cactorum has not provided complete control of O. stricta in KNP, the moderate levels of larval damage have stunted the growth of O. stricta and have considerably extended the time that the young plants take to reach sexual maturity.
6. Comparisons of modelled (i.e. with no C. cactorum ) and actual populations of O. stricta showed that C. cactorum is making a substantial contribution to the control of O. stricta in residual infestations of the weed that have been treated with herbicides.
7. The need for long-term evaluation studies in biological weed control is demon strated by the development of an integrated management programme for effective control of O. stricta .  相似文献   
5.
The present study describes the development of an alloplasmic haploid-inducer in durum wheat cv Cando. This cultivar possesses the homozygous wheat-rye translocation 1BL/1RS from the 6x-wheat cv Veery. The nucleus of 4x-Cando-Veery 1BL/1RS was introduced into Aegilops kotschyi cytoplasm by initially using (kotschyi)-Salmon as the maternal parent. In the cross of this alloplasmic durum line with Cando-Veery 1BL/1RS, which was used as the recurrent pollen parent, haploids (n=14) were produced. The frequency of haploids increased from 5.7% in the F1 generation to 14% in the BC1 generation. The presence of rye chromosome arm 1RS and the concomitant loss of 1BS in (kotschyi)-Cando-Veery 1BL/1RS are necessary for haploid induction. Proposals are made which may enable the use of haploids produced by nucleo-cytoplasmic interactions in future wheat breeding programs.  相似文献   
6.
Summary C-banding patterns and nucleolar activity were analyzed in Dasypyrum villosum, its added chromosomes to hexaploid wheat and the hexaploid amphiploid Triticum dicoccum-D. villosum. Two different populations of the allogamous species D. villosum (2n= 14, VV) from Greece and Italy were analyzed showing a similar polymorphism for C-banding pattern. Six of the seven addition lines were identified by their characteristic C-banding pattern. No polymorphism between both members of each added alien chromosome was found. Furthermore, nucleolar activity and competition were studied by using silver staining procedure. In D. villosum only one chromosome pair, A, was found to be responsible for organizing nucleoli. The results obtained in the amphiploid and in the addition lines demonstrate that nucleolar activity is restricted to SAT-chromosomes 1B and 6B of wheat, while those of D. villosum remain inactive.  相似文献   
7.
8.
Globally, rain-fed wetlands provide critical habitat for a wide range of amphibian species, however, information on the use of rain-fed wetlands by Australian frog species is extremely limited. This study examined the distribution of frog breeding in rain-fed wetlands following the first significant rain event after a period of severe drought (2002–2009) in order to predict how frog communities may be affected in the future by changed climate. Tadpole communities along with vegetation and water quality variables were described in 35 rain-fed wetlands across the South West Slopes and Riverina bioregions of inland south-eastern Australia. In addition, weekly tadpole surveys were conducted in a subset of these wetlands to describe temporal patterns of occupancy. Despite the protracted dry period prior to this study 50% of the rain-fed wetlands surveyed contained tadpoles. However, frog communities were species poor with only five species recorded. The majority of wetlands were dominated be a single species, Limnodynastes tasmaniensis which is also common within permanent waterbodies such as farm dams and irrigation infrastructure in both bioregions. Tadpoles of two burrowing species L. interioris and Neobatrachus sudelli were restricted to a small number of wetlands mostly in the South West Slopes. The composition of tadpole communities changed over time, and Crinia parinsignifera was the only species that continued to breed over winter. The dominance of generalist species within rain-fed wetlands indicates that characteristics such as dispersal capability, flexibility in breeding times and the ability to utilise created habitats may be more important than burrowing ability and longevity when predicting vulnerability to climate change.  相似文献   
9.
The c-myc gene encodes superimposed RNA polymerase II and III promoters   总被引:25,自引:0,他引:25  
J Chung  D J Sussman  R Zeller  P Leder 《Cell》1987,51(6):1001-1008
  相似文献   
10.
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