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   4200篇
  免费   176篇
  国内免费   228篇
化学   1125篇
晶体学   9篇
力学   49篇
综合类   21篇
数学   2038篇
物理学   1362篇
  2023年   22篇
  2022年   90篇
  2021年   94篇
  2020年   64篇
  2019年   55篇
  2018年   72篇
  2017年   72篇
  2016年   59篇
  2015年   51篇
  2014年   77篇
  2013年   263篇
  2012年   150篇
  2011年   336篇
  2010年   243篇
  2009年   468篇
  2008年   439篇
  2007年   361篇
  2006年   377篇
  2005年   231篇
  2004年   116篇
  2003年   81篇
  2002年   190篇
  2001年   142篇
  2000年   118篇
  1999年   71篇
  1998年   76篇
  1997年   40篇
  1996年   63篇
  1995年   29篇
  1994年   35篇
  1993年   8篇
  1992年   12篇
  1991年   10篇
  1990年   4篇
  1989年   7篇
  1988年   5篇
  1987年   5篇
  1986年   3篇
  1985年   6篇
  1984年   5篇
  1983年   5篇
  1981年   7篇
  1980年   7篇
  1979年   8篇
  1978年   5篇
  1977年   3篇
  1975年   3篇
  1974年   2篇
  1973年   6篇
  1959年   2篇
排序方式: 共有4604条查询结果,搜索用时 15 毫秒
81.
Additive manufacturing technologies, generally grouped under the name of 3D printing, are experiencing an explosion of interest during the last few years. The possibility of fast prototyping enabled by 3D printing has been recognized as a crucial booster for device fabrication and general scientific advancements. In this review, attention is focused on the latest developments in the field of redox flow batteries which are, similar to other energy related devices, characterized by the recent adoption of 3D printing methods for the fabrication of key components. Whether simply to investigate flow phenomena, test new designs or fabricate final-product components with custom features, the use of 3D printing can critically drive this field of research towards better performing energy-storage systems. The latest and most representative examples of redox flow battery studies will be discussed, categorized in relation to the electrolyte used and whether the devices are employed in aqueous or non-aqueous applications.  相似文献   
82.
Many proteins in living organisms are glycosylated. As their glycan patterns exhibit protein-, cell-, and tissue-specific heterogeneity, changes in the glycosylation levels could serve as useful indicators of various pathological and physiological states. Thus, the identification of glycoprotein biomarkers from specific changes in the glycan profiles of glycoproteins is a trending field. Lectin microarrays provide a new glycan analysis platform, which enables rapid and sensitive analysis of complex glycans without requiring the release of glycans from the protein. Recent developments in lectin microarray technology enable high-throughput analysis of glycans in complex biological samples. In this review, we will discuss the basic concepts and recent progress in lectin microarray technology, the application of lectin microarrays in biomarker discovery, and the challenges and future development of this technology. Given the tremendous technical advancements that have been made, lectin microarrays will become an indispensable tool for the discovery of glycoprotein biomarkers.  相似文献   
83.
Tatsuaki Wada 《Physics letters. A》2011,375(20):2037-2040
Gauss? principle in statistical mechanics is generalized for a q-exponential distribution in nonextensive statistical mechanics. It determines the associated stochastic and statistical nonextensive entropies which satisfy Greene-Callen principle concerning on the equivalence between microcanonical and canonical ensembles.  相似文献   
84.
We report first-principles calculations of the current-voltage characteristic and the conductance of carbon-based molecular wires with different length capped with sulfur ends between two metallic electrodes made of different metals. The optimized molecular structure of carbon chain in the junction is presented on the structure of polyyne. The conductance of the polyyne wires shows oscillatory behavior depending on the number of carbon atoms (triple bonds). Current rectification is found and rectification direction presents inversion with the odd and even number of carbon atoms.  相似文献   
85.
We generalize the usual two-strategy prisoner?s dilemma game to a multi-strategy game, in which the strategy variable s is allowed to take q different fractional values lying between 0 and 1. The fractional-valued strategies signify that individuals are not absolutely cooperative or defective, instead they can adopt intermediate strategies. Simulation results on 1D and 2D lattices show that, compared with the binary strategy game, the multi-strategy game can sustain cooperation in more stringent defective environments. We give a comprehensive analysis of the distributions of the survived strategies and we compare pairwise the relative strength and weakness of different strategies. It turns out that some intermediate strategies survive the pure defection because they can reduce being exploited and at the same time benefit from the spatial reciprocity effect. Our work may shed some light on the intermediate behaviors in human society.  相似文献   
86.
We discuss Hardy?s paradox and weak measurements by using multitasking diagrams, which are introduced to illustrate the progress of quantum probabilities through the double interferometer system. We explain how Hardy?s paradox is avoided and elaborate on the outcome of weak measurements in this context.  相似文献   
87.
新型锥透镜产生局域空心光束   总被引:6,自引:0,他引:6       下载免费PDF全文
张前安  吴逢铁  郑维涛  马亮 《物理学报》2011,60(9):94201-094201
首次提出产生局域空心光束(Bottle beam)的另一类新型锥透镜模型.讨论了凹凸两种模型,分别是在传统轴棱锥的底部磨削和胶合圆台结构形成.研究结果表明平面波正入射新型凹锥透镜可产生单个Bottle beam,正入射新型凸锥透镜可形成具有周期性的Bottle beam.通过几何光学分析了产生Bottle beam的原理,计算了Bottle beam的相关参数.由衍射积分理论分析和模拟了新型锥透镜后的光强分布特性,所得分析结果与几何光学分析基本符合. 关键词: 新型锥透镜 Bottle beam 轴棱锥 Bessel光  相似文献   
88.
A novel approach to prepare 4-anilinoquinazoline derivatives based on the transformation of indoline-2,3-dione to formamidine was developed. The processes with this approach are simple, efficient, and environmentally friendly. The efficiency of this approach was evaluated by synthesizing 17 4-anilinoquinazolines and comparing the obtained yields with those achievable through conventional synthetic methods. It was the first time that compounds 8d, 8e, 8h, and 13bf were synthesized. The characteristics of the IR and the UV spectra of these compounds and the effects of their substituents on the spectra were observed.  相似文献   
89.
Kre?n's formula provides a parametrization of the generalized resolvents and Štraus extensions of a closed symmetric operator with equal possibly infinite defect numbers in a Hilbert space in terms of Nevanlinna families in a parameter space. The aim of this note is to give a simple complete analytical proof of Kre?n's formula.  相似文献   
90.
Estimating Turán densities of hypergraphs is believed to be one of the most challenging problems in extremal set theory. The concept of ‘jump’ concerns the distribution of Turán densities. A number α∈[0,1) is a jump for r-uniform graphs if there exists a constant c>0 such that for any family F of r-uniform graphs, if the Turán density of F is greater than α, then the Turán density of F is at least α+c. A fundamental result in extremal graph theory due to Erd?s and Stone implies that every number in [0,1) is a jump for graphs. Erd?s also showed that every number in [0,r!/rr) is a jump for r-uniform hypergraphs. Furthermore, Frankl and Rödl showed the existence of non-jumps for hypergraphs. Recently, more non-jumps were found in [r!/rr,1) for r-uniform hypergraphs. But there are still a lot of unknowns regarding jumps for hypergraphs. In this paper, we propose a new but related concept-strong-jump and describe several sequences of non-strong-jumps. It might help us to understand the distribution of Turán densities for hypergraphs better by finding more non-strong-jumps.  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