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   668篇
  免费   63篇
  731篇
  2024年   1篇
  2023年   11篇
  2022年   15篇
  2021年   30篇
  2020年   28篇
  2019年   25篇
  2018年   18篇
  2017年   22篇
  2016年   27篇
  2015年   32篇
  2014年   45篇
  2013年   46篇
  2012年   69篇
  2011年   51篇
  2010年   38篇
  2009年   39篇
  2008年   39篇
  2007年   42篇
  2006年   31篇
  2005年   28篇
  2004年   20篇
  2003年   17篇
  2002年   15篇
  2001年   3篇
  2000年   3篇
  1999年   2篇
  1998年   10篇
  1997年   6篇
  1996年   5篇
  1995年   2篇
  1993年   3篇
  1992年   1篇
  1991年   1篇
  1990年   1篇
  1989年   1篇
  1988年   1篇
  1984年   1篇
  1981年   2篇
排序方式: 共有731条查询结果,搜索用时 671 毫秒
121.

This paper presents a simple multi-band metamaterial absorber for terahertz applications. The unit cell of the proposed structure consists of a single square ring having gaps at the centers on three of its sides. The proposed absorber produces three absorption bands for all polarizations and hence the design can be considered as insensitive to polarization variation. It provides an average absorption of 96.92% for the TE polarization with a peak absorption of 99.44% at 3.87 THz and for the TM polarization, it provides an average absorption of 98.4% with a peak absorption of 99.86% at 3.87 THz. An additional absorption peak is observed for the TE polarization at 1.055 THz that gradually diminishes with the increase in polarization angle and completely vanishes for the TM polarization. Thus, the structure displays a hybrid polarization response with polarization insensitivity in three bands and polarization sensitivity in one band. Parametric analysis has been carried out validating the optimal selection of the design parameters. The simplicity of the design and its combined polarization sensitive and polarization insensitive absorption characteristics can find tremendous applications in the field of terahertz imaging and sensing.

  相似文献   
122.
123.
124.
Parametric methods for identifying laterally transferred genes exploit the directional mutational biases unique to each genome. Yet the development of new, more robust methods—as well as the evaluation and proper implementation of existing methods—relies on an arbitrary assessment of performance using real genomes, where the evolutionary histories of genes are not known. We have used the framework of a generalized hidden Markov model to create artificial genomes modeled after genuine genomes. To model a genome, “core” genes—those displaying patterns of mutational biases shared among large numbers of genes—are identified by a novel gene clustering approach based on the Akaike information criterion. Gene models derived from multiple “core” gene clusters are used to generate an artificial genome that models the properties of a genuine genome. Chimeric artificial genomes—representing those having experienced lateral gene transfer—were created by combining genes from multiple artificial genomes, and the performance of the parametric methods for identifying “atypical” genes was assessed directly. We found that a hidden Markov model that included multiple gene models, each trained on sets of genes representing the range of genotypic variability within a genome, could produce artificial genomes that mimicked the properties of genuine genomes. Moreover, different methods for detecting foreign genes performed differently—i.e., they had different sets of strengths and weaknesses—when identifying atypical genes within chimeric artificial genomes.  相似文献   
125.

Background

Studies from high-income countries have shown that women receive less aggressive diagnostics and treatment than men in acute coronary syndromes (ACS), though their short-term mortality does not appear to differ from men. Data on gender differences in ACS presentation, management, and outcomes are sparse in India.

Methods and Results

The Detection and Management of Coronary Heart Disease (DEMAT) Registry collected data from 1,565 suspected ACS patients (334 women; 1,231 men) from ten tertiary care centers throughout India between 2007–2008. We evaluated gender differences in presentation, in-hospital and discharge management, and 30-day death and major adverse cardiovascular event (MACE; death, re-hospitalization, and cardiac arrest) rates. Women were less likely to present with STEMI than men (38% vs. 55%, p<0.001). Overall inpatient diagnostics and treatment patterns were similar between men and women after adjustment for potential confounders. Optimal discharge management with aspirin, clopidogrel, beta-blockers, and statin therapy was lower for women than men, (58% vs. 65%, p = 0.03), but these differences were attenuated after adjustment (OR = 0.86 (0.62, 1.19)). Neither the outcome of 30-day mortality (OR = 1.40 (0.62, 3.16)) nor MACE (OR = 1.00 (0.67, 1.48)) differed significantly between men and women after adjustment.

Conclusions

ACS in-hospital management, discharge management, and 30-day outcomes did not significantly differ between genders in the DEMAT registry, though consistently higher treatment rates and lower event rates in men compared to women were seen. These findings underscore the importance of further investigation of gender differences in cardiovascular care in India.  相似文献   
126.
本文首次分析了野鲮鱼 (Labeodyocheilus)等位酶的变异情况。通过对 17个酶系统的研究 ,发现 2 8个可以稳定检测的位点 ,其中 8个位点具有多态性。使用这 8个等位酶位点 ,分析了取自不同河流 ,即Satluj、Yamuna和Tons河的样本的遗传多样性情况。结果显示 ,不同样本间存在显著的遗传异质性 ,各位点的表观杂合度介于 0 0 392 (Yamuna河 )与 0 0 4 87(Tons河 )之间。因此 ,本研究所筛选出的多态性等位酶位点为研究该野鲮鱼的种群遗传结构奠定了基础  相似文献   
127.
High night temperature (HNT) is a major constraint to sustaining global rice production under future climate. Physiological and biochemical mechanisms were elucidated for HNT‐induced grain yield and quality loss in rice. Contrasting rice cultivars (N22, tolerant; Gharib, susceptible; IR64, high yielding with superior grain quality) were tested under control (23°C) and HNT (29°C) using unique field‐based tents from panicle initiation till physiological maturity. HNT affected 1000 grain weight, grain yield, grain chalk and amylose content in Gharib and IR64. HNT increased night respiration (Rn) accounted for higher carbon losses during post‐flowering phase. Gharib and IR64 recorded 16 and 9% yield reduction with a 63 and 35% increase in average post‐flowering Rn under HNT, respectively. HNT altered sugar accumulation in the rachis and spikelets across the cultivars with Gharib and IR64 recording higher sugar accumulation in the rachis. HNT reduced panicle starch content in Gharib (22%) and IR64 (11%) at physiological maturity, but not in the tolerant N22. At the enzymatic level, HNT reduced sink strength with lower cell wall invertase and sucrose synthase activity in Gharib and IR64, which affected starch accumulation in the developing grain, thereby reducing grain weight and quality. Interestingly, N22 recorded lower Rn‐mediated carbon losses and minimum impact on sink strength under HNT. Mechanistic responses identified will facilitate crop models to precisely estimate HNT‐induced damage under future warming scenarios.  相似文献   
128.
Cultivated peanut is grown worldwide as richsource of oil and protein. A broad genetic base is needed for cultivar improvement. The objectives of this study were to develop highly informative simple sequence repeat(SSR)markers and to assess the genetic diversity and population structure of peanut cultivars and breeding lines from different breeding programs in China, India and the US. A total of 111 SSR markers were selected for this study, resulting in a total of 472 alleles. The mean values of gene diversity and polymorphic information content(PIC) were 0.480 and 0.429, respectively.Country-wise analysis revealed that alleles per locus in three countries were similar. The mean gene diversity in the US,China and India was 0.363, 0.489 and 0.47 with an average PIC of 0.323, 0.43 and 0.412, respectively. Genetic analysis using the STRUCTURE divided these peanut lines into two populations(P_1, P_2), which was consistent with the dendrogram based on genetic distance(G_1, G_2) and the clustering of principal component analysis. The groupings were related to peanut market types and the geographic origin with a few admixtures. The results could be used by breeding programs to assess the genetic diversity of breeding materials to broaden the genetic base and for molecular genetics studies.  相似文献   
129.
130.
Rapid prototyping of distributed systems can be achieved by integrating commercial off-the-shelf (COTS) components. With components as the building blocks, it is important to predict the performance of the system based on the performance of individual components. In this paper, performance prediction of a system consisting of a small number of components is investigated under different inter-component communication patterns, and the number of threads provided by components. Based on the experimental results, it can be inferred that the proposed composition rules provide a reasonably accurate prediction of the performance of a system made out of these components.
Barrett R. BryantEmail:
  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