全文获取类型
收费全文 | 635篇 |
免费 | 10篇 |
专业分类
化学 | 365篇 |
晶体学 | 7篇 |
力学 | 38篇 |
数学 | 122篇 |
物理学 | 113篇 |
出版年
2021年 | 4篇 |
2020年 | 3篇 |
2019年 | 4篇 |
2017年 | 3篇 |
2016年 | 6篇 |
2015年 | 13篇 |
2014年 | 12篇 |
2013年 | 34篇 |
2012年 | 26篇 |
2011年 | 31篇 |
2010年 | 32篇 |
2009年 | 15篇 |
2008年 | 36篇 |
2007年 | 34篇 |
2006年 | 28篇 |
2005年 | 22篇 |
2004年 | 27篇 |
2003年 | 28篇 |
2002年 | 18篇 |
2001年 | 12篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 8篇 |
1997年 | 7篇 |
1996年 | 12篇 |
1995年 | 8篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 8篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 13篇 |
1981年 | 12篇 |
1980年 | 8篇 |
1979年 | 18篇 |
1978年 | 9篇 |
1977年 | 10篇 |
1976年 | 4篇 |
1974年 | 5篇 |
1973年 | 8篇 |
1972年 | 7篇 |
1970年 | 4篇 |
1969年 | 3篇 |
1962年 | 5篇 |
排序方式: 共有645条查询结果,搜索用时 437 毫秒
21.
Andreas Meister Sigrun Ortleb Thomas Sonar Martina Wirz 《Journal of computational physics》2012,231(23):7722-7729
This paper gives a first numerical comparison of the Discontinuous-Galerkin-(DG) and Spectral-Difference-Method (SD) under almost equivalent conditions for smooth test cases. 相似文献
22.
Andrés Alessandro León Baldelli Blaise Bourdin Jean-Jacques Marigo Corrado Maurini 《Continuum Mechanics and Thermodynamics》2013,25(2-4):243-268
We study multi-fissuration and debonding phenomena of a thin film bonded to a stiff substrate using the variational approach to fracture mechanics. We consider a reduced one-dimensional membrane model where the loading is introduced through uniform inelastic (e.g., thermal) strains in the film or imposed displacements of the substrate. Fracture phenomena are accounted for by adopting a Griffith model for debonding and transverse fracture. On the basis of energy minimization arguments, we recover the key qualitative properties of the experimental evidences, like the periodicity of transverse cracks and the peripheral debonding of each regular segment. Phase diagrams relate the maximum number of transverse cracks that may be created before debonding takes place, as a function of the material properties and the sample’s geometry. The theoretical results are illustrated with numerical simulations obtained through a finite element discretization and a regularized variational formulation of the Ambrosio–Tortorelli type, which is suited to further extensions in two-dimensional settings. 相似文献
23.
Aaron Breivogel Michael Meister Dr. Christoph Förster Dr. Frédéric Laquai Prof. Dr. Katja Heinze 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(41):13745-13760
The synergy of push–pull substitution and enlarged ligand bite angles has been used in functionalized heteroleptic bis(tridentate) polypyridine complexes of ruthenium(II) to shift the 1MLCT absorption and the 3MLCT emission to lower energy, enhance the emission quantum yield, and to prolong the 3MLCT excited‐state lifetime. In these complexes, that is, [Ru(ddpd)(EtOOC‐tpy)][PF6]2, [Ru(ddpd‐NH2)(EtOOC‐tpy)][PF6]2, [Ru(ddpd){(MeOOC)3‐tpy}][PF6]2, and [Ru(ddpd‐NH2){(EtOOC)3‐tpy}][PF6]2 the combination of the electron‐accepting 2,2′;6′,2′′‐terpyridine (tpy) ligand equipped with one or three COOR substituents with the electron‐donating N,N′‐dimethyl‐N,N′‐dipyridin‐2‐ylpyridine‐2,6‐diamine (ddpd) ligand decorated with none or one NH2 group enforces spatially separated and orthogonal frontier orbitals with a small HOMO–LUMO gap resulting in low‐energy 1MLCT and 3MLCT states. The extended bite angle of the ddpd ligand increases the ligand field splitting and pushes the deactivating 3MC state to higher energy. The properties of the new isomerically pure mixed ligand complexes have been studied by using electrochemistry, UV/Vis absorption spectroscopy, static and time‐resolved luminescence spectroscopy, and transient absorption spectroscopy. The experimental data were rationalized by using density functional calculations on differently charged species (charge n=0–4) and on triplet excited states (3MLCT and 3MC) as well as by time‐dependent density functional calculations (excited singlet states). 相似文献
24.
25.
Thi Thu Van Nguyen Jean-Jacques Strodiot Van Hien Nguyen 《Journal of Global Optimization》2009,44(2):175-192
In this article we present a new and efficient method for solving equilibrium problems on polyhedra. The method is based on
an interior-quadratic proximal term which replaces the usual quadratic proximal term. This leads to an interior proximal type
algorithm. Each iteration consists in a prediction step followed by a correction step as in the extragradient method. In a
first algorithm each of these steps is obtained by solving an unconstrained minimization problem, while in a second algorithm
the correction step is replaced by an Armijo-backtracking linesearch followed by an hyperplane projection step. We prove that
our algorithms are convergent under mild assumptions: pseudomonotonicity for the two algorithms and a Lipschitz property for
the first one. Finally we present some numerical experiments to illustrate the behavior of the proposed algorithms. 相似文献
26.
27.
Jean-Jacques Aaron Zouhair Mechbal Alain Adenier Cyril Parkanyi Vaclav Kozmik Jiri Svoboda 《Journal of fluorescence》2002,12(2):231-239
The structural and solvent effects on the electronic absorption and fluorescence spectra, and fluorescence quantum yields, of four new fused benzothiophene derivatives, including benzothieno[3,2b]-thiophene (BTT), benzothieno[3,2-b]benzothiophene (BTBT), 6-methoxy[1]benzothieno[3,2b]-thiophene (MeOBTT), and benzothieno[3,2-b]indole (BTI) were investigated at 295 K. The luminescence properties of the corresponding conductive oligomers, poly(BTT) and poly (MeOBTT), electrosynthesized in acetonitrile, were also studied. Satisfactory McRae, Suppan, and Kawski-Chamma-Viallet solvatochromic correlations were established for the four monomers in most solvents. A weak negative solvatochromic behavior was found for these compounds, indicating that their dipole moments are slightly lower in the excited singlet state than in the ground state. Kamlet-Abboud-Taft multiparametric correlations were also obtained for absorption and fluorescence wave numbers and quantum yields, demonstrating the existence of specific solute-solvent interactions. In the case of the oligomers, important red-shifts of the fluorescence emission maxima ( 90–110 nm) relative to the corresponding monomers were observed, which shows the extent of conjugated segments in the oligomer chains. 相似文献
28.
29.
Bruce A. Carlson Jean-Jacques Katz Herbert C. Brown 《Journal of organometallic chemistry》1974,67(2):C39-C42
Treatment of hindered borinic esters, R2 BOR′; with an equimolar quantity of α,α-dichloromethyl methyl ether and lithium triethylcarboxide yields the α-chloroboronic esters, R2 CHClB(OCH3)OR′, in excellent yields. In cases where the steric requirements of R are not sufficient, the steric requirements of R′ can be increased to achieve the synthesis. 相似文献
30.