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   24767篇
  免费   971篇
  国内免费   919篇
化学   7185篇
晶体学   879篇
力学   696篇
综合类   70篇
数学   14508篇
物理学   3319篇
  2023年   198篇
  2022年   214篇
  2021年   245篇
  2020年   383篇
  2019年   650篇
  2018年   624篇
  2017年   582篇
  2016年   551篇
  2015年   516篇
  2014年   797篇
  2013年   2226篇
  2012年   1081篇
  2011年   1673篇
  2010年   1625篇
  2009年   1685篇
  2008年   1734篇
  2007年   1641篇
  2006年   1364篇
  2005年   1056篇
  2004年   964篇
  2003年   812篇
  2002年   602篇
  2001年   451篇
  2000年   371篇
  1999年   404篇
  1998年   326篇
  1997年   345篇
  1996年   394篇
  1995年   327篇
  1994年   350篇
  1993年   302篇
  1992年   236篇
  1991年   140篇
  1990年   119篇
  1989年   123篇
  1988年   83篇
  1987年   100篇
  1986年   105篇
  1985年   201篇
  1984年   160篇
  1983年   102篇
  1982年   129篇
  1981年   112篇
  1980年   108篇
  1979年   72篇
  1978年   89篇
  1977年   85篇
  1976年   78篇
  1975年   27篇
  1974年   34篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
A finite support product of ω1 clones of Jensen's minimal Π21 singleton forcing is used to define a model in which any non-empty analytically definable set of reals contains an analytically definable real (the full basis theorem), but there is no analytically definable wellordering of the reals.  相似文献   
2.
We solve a combinatorial question concerning eigenvalues of the universal intertwining endomorphism of a subset representation.  相似文献   
3.
4.
Luca Cimbaro 《哲学杂志》2019,99(12):1499-1514
A unified theory captures both brittle and ductile fracture. The fracture toughness is proportional to the applied stress squared and the length of the crack. For purely brittle solids, this criterion is equivalent to Griffith's theory. In other cases, it provides a theoretical basis for the Irwin-Orowan formula. For purely ductile solids, the theory makes direct contact with the Bilby-Cottrell-Swinden model. The toughness is highest in ductile materials because the shielding dislocations in the plastic zone provide additional resistance to crack growth. This resistance is the force opposing dislocation motion, and the Peach-Koehler force overcomes it. A dislocation-free zone separates the plastic zone from and the tip of the crack. The dislocation-free zone is finite because molecular forces responsible for the cohesion of the surfaces near the crack tip are not negligible. At the point of crack growth, the length of the dislocation-free zone is constant and the shielding dislocations advance in concert. As in Griffith's theory, the crack is in unstable equilibrium. The theory shows that a dimensionless variable controls the elastoplastic behaviour. A relationship for the size of the dislocation-free zone is derived in terms of the macroscopic and microscopic parameters that govern the fracture.  相似文献   
5.
Parkinson's disease is a neurodegenerative disorder involving a functional protein, α-synuclein, whose primary function is related to vesicle trafficking. However, α-synuclein is prone to form aggregates, and these inclusions, known as Lewy bodies, are the hallmark of Parkinson's disease. α-synuclein can alter its conformation and acquire aggregating capacity, forming aggregates containing β-sheets. This protein's pathogenic importance is based on its ability to form oligomers that impair synaptic transmission and neuronal function by increasing membrane permeability and altering homeostasis, generating a deleterious effect over cells. First, we establish that oligomers interfere with the mechanical properties of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) membrane, as demonstrated by nanoindentation curves. In contrast, nanoindentation revealed that the α-synuclein monomer's presence leads to a much more resistant lipid bilayer. Moreover, the oligomers’ interaction with cell membranes can promote lactate dehydrogenase (LDH) release, suggesting the activation of cytotoxic events.  相似文献   
6.
7.
In this paper, we propose a sufficient and necessary condition for the boundedness of all the solutions for the equation x¨+n2x+g(x)=p(t) with the critical situation that |02πp(t)e?intdt|=2|g(+)?g(?)| on g and p, where nN+, p(t) is periodic and g(x) is bounded.  相似文献   
8.
The present review discusses the theory and application of van't Hoff analysis in chiral chromatography, with main focus on liquid chromatography. The topics considered include the physical meaning of van't Hoff equation's parameters, interpretation of thermodynamic data in terms of retention and enantioseparation mechanisms, abnormal behavior of van't Hoff plots, and best practices to avoid biased results.  相似文献   
9.
10.
Nonclassical light states are important for both conceptual and practical reasons: they are basic ingredients in testing and exploring quantum foundations, and are crucial resources in quantum technologies. Various useful criteria have been developed to detect nonclassicality in the literature, and several meaningful measures of nonclassicality have been introduced and measured experimentally. In this work, by use of a non-Hermitian generalization of the Wigner-Yanase-Dyson skew information and playing with operator ordering in evaluating average photon number, we develop a novel family of criteria for detecting nonclassicality of light based on Lieb's concavity, which is a deep and powerful result concerning interaction between quantum states and observables. We elucidate the information-theoretic as well as the physical meaning of the criteria, and illustrate their effectiveness in capturing and quantifying nonclassicality of various important light states.  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