全文获取类型
收费全文 | 2021篇 |
免费 | 2篇 |
国内免费 | 11篇 |
专业分类
化学 | 1384篇 |
晶体学 | 12篇 |
力学 | 28篇 |
数学 | 352篇 |
物理学 | 258篇 |
出版年
2022年 | 11篇 |
2020年 | 14篇 |
2019年 | 7篇 |
2018年 | 13篇 |
2017年 | 9篇 |
2016年 | 13篇 |
2015年 | 11篇 |
2014年 | 21篇 |
2013年 | 104篇 |
2012年 | 83篇 |
2011年 | 97篇 |
2010年 | 73篇 |
2009年 | 41篇 |
2008年 | 103篇 |
2007年 | 106篇 |
2006年 | 125篇 |
2005年 | 133篇 |
2004年 | 112篇 |
2003年 | 94篇 |
2002年 | 79篇 |
2001年 | 16篇 |
2000年 | 22篇 |
1999年 | 21篇 |
1998年 | 21篇 |
1997年 | 32篇 |
1996年 | 33篇 |
1995年 | 16篇 |
1994年 | 35篇 |
1993年 | 32篇 |
1992年 | 15篇 |
1991年 | 21篇 |
1990年 | 23篇 |
1989年 | 20篇 |
1988年 | 21篇 |
1987年 | 18篇 |
1986年 | 17篇 |
1985年 | 30篇 |
1984年 | 31篇 |
1983年 | 15篇 |
1982年 | 53篇 |
1981年 | 41篇 |
1980年 | 36篇 |
1979年 | 34篇 |
1978年 | 30篇 |
1977年 | 36篇 |
1976年 | 25篇 |
1975年 | 18篇 |
1974年 | 19篇 |
1973年 | 13篇 |
1971年 | 8篇 |
排序方式: 共有2034条查询结果,搜索用时 15 毫秒
141.
Dominique Petit Jean-Pierre Korb Pierre Levitz Jean LeBideau David Brevet 《Comptes Rendus Chimie》2010,13(4):409-411
We present the first results of the nuclear magnetic relaxation dispersion (NMRD) of the confined proton-bearing cation (BMI) and fluorine-bearing anion (TFSI) pair of ionic liquids (Li+-ionogels) confined within a silica-like mesoporous matrices designed for lithium batteries. These results are in favour of a very-correlated dynamical motion of the anion–cation pair within the solid and disordered silica matrix. 相似文献
142.
Olfa Labidi Rose-Noëlle Vannier Jean-Pierre Wignacourt 《Journal of solid state chemistry》2008,181(9):2268-2273
Reinvestigation of PbBiOXO4 (X=V, P, As) thermal behaviour revealed a phase transition for V- and P-compounds, but no transition for the As-compound. As shown by single-crystal X-ray diffraction and high-resolution neutron powder diffraction, α-PbBiOVO4 transforms to β-PbBiOVO4 at 550 °C. The two PbBiOPO4 varieties are isomorph to the vanadate forms, while PbBiOAsO4 adopts the β-type structure whatever the temperature. PbBiP1−xOAsxO4 and PbBiV1−xOMxO4 (M=As, P, Cr, Mn) solid solutions display both triclinic and monoclinic domains, and the α→β transition temperature is a function of the substitution rate. The ionic conductivity of these compounds was investigated by impedance spectroscopy. The analysis of free space in the β-PbBiOVO4 structure allows to propose a one-dimensional oxygen diffusion pathway along [010] when the temperature increases. 相似文献
143.
Jean-Pierre Dussault 《Computational Optimization and Applications》2009,44(3):373-383
We refine the speed of convergence analysis for the quadratic augmented penalty algorithm. We improve the convergence order
from 4/3 to 3/2 for the first order multiplier iteration. For the second order iteration, we generalize the analysis, and
consider a primal–dual variant which asymptotically reduces to a Newton step for the optimality conditions. 相似文献
144.
145.
N. Ressayre 《Transformation Groups》2005,10(2):255-265
Let G be a connected reductive algebraic group defined on an algebraically
closed field k of characteristic different from 2. Let B denote the flag variety of G. Let H be a spherical subgroup of G.
F. Knop defined an action of the Weyl group W of G on the finite set of the H-orbits in B. Here, we define an invariant, namely
the type, separating the orbits of W. 相似文献
146.
Fabien Durola Jean-Pierre Sauvage Oliver S. Wenger 《Coordination chemistry reviews》2010,254(15-16):1748-1759
The use of 8,8′-diaryl-substituted 3,3′-biisoquinolines allows the construction of new multi-component assemblies that are inaccessible with the 2,9-diaryl-substituted 1,10-phenanthroline ligands previously developed by the Sauvage group. This is due to the sterically non-hindering nature of the new chelates, which makes three-component entanglements around octahedral metal centres such as iron(II), cobalt(II) and ruthenium(II) readily possible. Among the newly synthesized molecular assemblies are [3]rotaxanes and [3]pseudorotaxanes in which two molecular strings pass through a single macrocycle, as well as molecular shuttles that exhibit greatly improved shuttling kinetics when compared to previously investigated molecular machines that are based on copper(I)/copper(II) redox chemistry. 相似文献
147.
Two original dinuclear (LnYb, 3 and LnEr, 4) and one trinuclear CuIILnIIICuII (LnGd, 5) complexes derived from a polydentate non symmetrical Schiff base ligand H2L have been prepared. The ligand possesses two functions (phenol and oxime) able to coordinate the Ln ions, but structural studies (X-ray diffraction and powder X-ray diffraction) show that the CuII and LnIII ions are only bridged by the oximato (NO) pair. The missing phenoxo bridge is replaced by a surprising pseudo-bridge involving one oxygen atom of the nitrato anion linked to the Cu and Ln ions according to a η2: η1: μ mode. Although this latter contact has no role from the magnetic point of view, it introduces a large deformation of the unique bridging network. The CuYb complex 3 and the trinuclear CuGdCu complex 5 present antiferromagnetic interactions, with a JCuGd interaction equal to ?1.25 cm?1 in 5. The genuine single bridge can be considered as responsible for the antiferromagnetic character of the interaction. 相似文献
148.
Jean-Yves Raty Céline Otjacques Jean-Pierre Gaspard Christophe Bichara 《Solid State Sciences》2010,12(2):193-198
Ge1Sb2Te4 is one of the most commonly used phase change materials, due to the large optical and electrical contrast between a metastable crystalline phase and the amorphous phase. We use ab initio molecular dynamics to generate an amorphous Ge1Sb2Te4 structure. By analysing the distance distributions, we show that the structure can be analysed in terms of 21% of tetrahedrally coordinated Ge atoms and 79% of 3-fold Ge atoms. These are involved in distorted octahedral shells with bond length correlations that are similar to the a-GeTe structure as a consequence of a Peierls-distortion. The electronic properties are shown to be in reasonable agreement with the experiment with an electronic gap of 0.45 eV with. The optical conductivity curve is also in agreement with the experiment, with a maximal conductivity at an energy of ~3 eV. 相似文献
149.
Mamadalieva NZ Janibekov AA Girault JP Lafont R 《Natural product communications》2010,5(10):1579-1582
Chemical investigations of Silene viridiflora (L.) yielded a new ecdysteroid, 20-hydroxyecdysone 20,22-monoacetonide-25-acetate (1), and a known ecdysteroid, 2-deoxypolypodine B-3-beta-D-glucoside (2). The elucidation of the chemical structures was established by 1D and 2D NMR experiments. 相似文献
150.
This paper presents a mathematical design methodology for determining the shape of a trumpet air column that has near-perfect harmonicity, whose components are discontinuity-free, and whose input impedance peak heights are balanced over the playing range. The simulation model employed assumes linear wave propagation and uses cylindrical element discretization with a plane wave approximation. Acoustic measurements are made using a test set-up with an estimated relative measurement error of ±3 cents. Comparisons of measured results are given for the presented design (Macaluso trumpet) and the same trumpet air column with the bell replaced by a commercially used generic trumpet bell of unknown shape (Generic trumpet). For acoustic resonance modes 2-13 (233-1515 Hz), the measured root-mean-square (rms) harmonicity deviation is 5 cents for the Macaluso trumpet, whereas it is 18 cents for the Generic trumpet. However, considering the estimated measurement uncertainty, each of those deviations is somewhat over-stated. For that same range of resonances, the rms deviation between measured and calculated resonance frequencies for the Macaluso trumpet is 3 cents, thus validating the presented simulation model and equations. 相似文献