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   3088篇
  免费   217篇
  3305篇
  2024年   2篇
  2023年   42篇
  2022年   79篇
  2021年   143篇
  2020年   105篇
  2019年   126篇
  2018年   120篇
  2017年   99篇
  2016年   147篇
  2015年   209篇
  2014年   202篇
  2013年   231篇
  2012年   246篇
  2011年   226篇
  2010年   138篇
  2009年   103篇
  2008年   156篇
  2007年   148篇
  2006年   134篇
  2005年   119篇
  2004年   97篇
  2003年   82篇
  2002年   68篇
  2001年   45篇
  2000年   18篇
  1999年   15篇
  1998年   21篇
  1997年   15篇
  1996年   17篇
  1995年   12篇
  1994年   12篇
  1993年   13篇
  1992年   14篇
  1991年   9篇
  1990年   8篇
  1989年   9篇
  1988年   8篇
  1987年   6篇
  1986年   8篇
  1985年   6篇
  1984年   7篇
  1983年   5篇
  1982年   11篇
  1981年   5篇
  1979年   3篇
  1978年   3篇
  1977年   4篇
  1974年   4篇
  1973年   1篇
  1968年   1篇
排序方式: 共有3305条查询结果,搜索用时 0 毫秒
1.
Genome-wide analysis of the SET DOMAIN GROUP family in grapevine   总被引:1,自引:0,他引:1  
The SET DOMAIN GROUP (SDG) proteins represent an evolutionarily-conserved family of epigenetic regulators present in eukaryotes and are putative candidates for the catalysis of lysine methylation in histones. Plant genomes analyses of this family have been performed in arabidopsis, maize, and rice and functional studies have shown that SDG genes are involved in the control of plant development. In this work, we describe the identification and structural characterization of SDG genes in the Vitis vinifera genome. This analysis revealed the presence of 33 putative SDG genes that can be grouped into different classes, as it has been previously described for plants. In addition to the SET domain, the proteins identified possessed other domains in the different classes. As part of our study regarding the growth and development of grapevine, we selected eight genes and their expression levels were analyzed in representative vegetative and reproductive organs of this species. The selected genes showed different patterns of expression during inflorescence and fruit development, suggesting that they participate in these processes. Furthermore, we showed that the expression of selected SDGs changes during viral infection, using as a model Grapevine Leafroll Associated Virus 3-infected symptomatic grapevine leaves and fruits. Our results suggest that developmental changes caused by this virus could be the result of alterations in SDG expression.  相似文献   
2.
The potential for reducing the occurrence of shallow landslides through targeted reforestation of critical parts of a river basin is explored through mathematical modelling. Through the systematic investigation of land management options, modelling allows the optimum strategies to be selected ahead of any real intervention in the basin. Physically based models, for which the parameters can be evaluated using physical reasoning, offer particular advantages for predicting the effects of possible future changes in land use and climate. Typically a physically based landslide model consists of a coupled hydrological model (for soil moisture) and a geotechnical slope stability model, along with an impact model, such as basin sediment yield. An application of the SHETRAN model to the 65.8-km2 Guabalcón basin in central Ecuador demonstrates a technique for identifying the areas of a basin most susceptible to shallow landsliding and for quantifying the effects of different vegetation covers on landslide incidence. Thus, for the modelled scenario, increasing root cohesion from 300 to 1500 Pa causes a two-thirds reduction in the number of landslides. Useful information can be obtained even on the basis of imperfect data availability but model output should be interpreted carefully in the light of parameter uncertainty.  相似文献   
3.
4.
Reduced noradrenaline turnover in brown adipose tissue of lactating rats   总被引:3,自引:0,他引:3  
Brown adipose tissue properties as well as noradrenaline turnover in the tissue were determined in 15-day lactating rats and virgin controls. Brown adipose tissue thermogenic activity was reduced in lactating rats as shown by a decrease in weight, cytochrome oxidase activity and mitochondrial GDP-binding. The noradrenaline turnover rate was lower in brown adipose tissue from lactating rats. It is suggested that diminished sympathetic activity in brown adipose tissue may be a major cause of the reduced tissue thermogenic activity during lactation.  相似文献   
5.
With the eventual goal of characterizingLegionella pneumophila serogroup 1 plasmids at the molecular level, we have analyzed the plasmid contents of 78 clinical and environmental Spanish isolates. After selection of a suitable alkaline lysis method, we detected plasmids with approximate molecular weights of 25, 36, 40, 61, 80, 85, 90, and 95 megadalton (MDal). Several factors (i.e., wide temporal and geographic distribution, high frequency in both clinical and environmental isolates, and apparent high copy number after subculturing) make the 36 MDal type IA plasmid an appropriate plasmid for further molecular studies.  相似文献   
6.
Tracheal insufflation of tumor necrosis factor (TNF; 5 micrograms or 1.2 x 10(5) U) markedly enhanced the survival of adult rats exposed to 100% O2: 12 of 17 rats (71%) survived for greater than 11 days, whereas 30 of 30 control (Hanks' balanced salt solution) insufflated rats (100%) died within 3 days of O2 exposure. Insufflation of gamma-interferon (5 micrograms) or intraperitoneal injection of up to 40 micrograms TNF did not afford any protection. At 55 h after O2 exposure, TNF-insufflated rats showed less pulmonary edema, as determined by the extravascular lung water content-to-bloodless lung dry weigh ratio and less alveolar capillary leak as determined by the protein content in the bronchoalveolar lavage fluid, than control insufflated rats similarly exposed. This protection against O2 toxicity by TNF insufflation was associated with increased lung superoxide dismutase, catalase, and glutathione peroxidase activities. The enhancement of lung antioxidant enzyme activities was noted at 55 h of O2 exposure, when control animals began to die of O2 toxicity. This temporal relationship suggests that TNF-induced increase in antioxidant enzyme activities contributes, at least in part, to the observed protection.  相似文献   
7.
Natural aggregates of Baby Hamster Kidney cells were grown in stirred vessels operated as repeated-batch cultures during more than 600 hours. Different protocols were applied to passaging different fractions of the initial culture: single cells, large size distributed aggregates and large aggregates. When single cells or aggregates with the same size distribution found in culture are used as inoculum, it is possible to maintain semi-continuous cultures during more than 600 hours while keeping cell growth and viability. These results suggest that aggregate culture in large scale might be feasible, since a small scale culture can easily be used as inoculum for larger vessels without noticeable modification of the aggregate chacteristics. However, when only the large aggregates are used as inoculum, it was shown that much lower cell concentrations are obtained, cell viability in aggregates dropping to less than 60%. Under this selection procedure, aggregates maintain a constant size, larger than under batch experiments, up to approximately 400 hours; after this time, aggregate size increases to almost twice the size expected from batch cultures.  相似文献   
8.
Soil micronutrients are capital for the delivery of ecosystem functioning and food provision worldwide. Yet, despite their importance, the global biogeography and ecological drivers of soil micronutrients remain virtually unknown, limiting our capacity to anticipate abrupt unexpected changes in soil micronutrients in the face of climate change. Here, we analyzed >1300 topsoil samples to examine the global distribution of six metallic micronutrients (Cu, Fe, Mn, Zn, Co and Ni) across all continents, climates and vegetation types. We found that warmer arid and tropical ecosystems, present in the least developed countries, sustain the lowest contents of multiple soil micronutrients. We further provide evidence that temperature increases may potentially result in abrupt and simultaneous reductions in the content of multiple soil micronutrients when a temperature threshold of 12–14°C is crossed, which may be occurring on 3% of the planet over the next century. Altogether, our findings provide fundamental understanding of the global distribution of soil micronutrients, with direct implications for the maintenance of ecosystem functioning, rangeland management and food production in the warmest and poorest regions of the planet.  相似文献   
9.
In the framework of the European project aimed at the sequencing of the Bacillus subtilis genome the DNA region located between gerB (314°) and sacXV (333°) was assigned to the Institut Pasteur. In this paper we describe the cloning and sequencing of a segment of 97 kb of contiguous DNA. Ninety-two open reading frames were predicted to encode putative proteins among which only forty-two were found to display significant similarities to known proteins present in databanks, e.g. amino acid permeases, proteins involved in cell wall or antibiotic biosynthesis, various regulatory proteins, proteins of several dehydrogenase families and enzymes II of the phosphotransferase system involved in sugar transport. Additional experiments led to the identification of the products of new B. subtilis genes, e.g. galactokinase and an operon involved in thiamine biosynthesis.  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