全文获取类型
收费全文 | 6102篇 |
免费 | 808篇 |
国内免费 | 1429篇 |
专业分类
化学 | 5738篇 |
晶体学 | 40篇 |
力学 | 458篇 |
综合类 | 67篇 |
数学 | 1009篇 |
物理学 | 1027篇 |
出版年
2024年 | 41篇 |
2023年 | 139篇 |
2022年 | 285篇 |
2021年 | 351篇 |
2020年 | 522篇 |
2019年 | 320篇 |
2018年 | 279篇 |
2017年 | 254篇 |
2016年 | 350篇 |
2015年 | 281篇 |
2014年 | 408篇 |
2013年 | 558篇 |
2012年 | 349篇 |
2011年 | 358篇 |
2010年 | 285篇 |
2009年 | 324篇 |
2008年 | 335篇 |
2007年 | 329篇 |
2006年 | 307篇 |
2005年 | 274篇 |
2004年 | 246篇 |
2003年 | 303篇 |
2002年 | 298篇 |
2001年 | 180篇 |
2000年 | 141篇 |
1999年 | 113篇 |
1998年 | 104篇 |
1997年 | 74篇 |
1996年 | 91篇 |
1995年 | 65篇 |
1994年 | 64篇 |
1993年 | 44篇 |
1992年 | 56篇 |
1991年 | 22篇 |
1990年 | 22篇 |
1989年 | 18篇 |
1988年 | 23篇 |
1987年 | 16篇 |
1986年 | 21篇 |
1985年 | 29篇 |
1984年 | 16篇 |
1983年 | 6篇 |
1982年 | 17篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1975年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有8339条查询结果,搜索用时 0 毫秒
21.
A scheme for teleporting a three-particle state is proposed when three pairs of entangled particles are used as quantum channels. Quantum teleportation can be successfully realized with a certain probability if the receiver adopts an appropriate unitary-reduction strategy. The probability of successful teleportation is determined by the smaller coetficients of the three entangled pairs. 相似文献
22.
The use of high-throughput techniques allowed the rapid identification of new catalysts for the enantioselective reduction of imines using polymethylhydrosiloxane (PMHS) as a reducing agent. By a simple modification of the chiral ligand structure that came out of the screening, the enantioselectivity of the reduction was increased from 40% ee to 60% ee. 相似文献
23.
THE COUPLING OF NATURAL BOUNDARY ELEMENT AND FINITE ELEMENT METHOD FOR 2D HYPERBOLIC EQUATIONS 总被引:2,自引:0,他引:2
De-haoYu Qi-kuiDu 《计算数学(英文版)》2003,21(5):585-594
In this paper, we investigate the coupling of natural boundary element and finite element methods of exterior initial boundary value problems for hyperbolic equations. The governing equation is first discretized in time, leading to a time-step scheme, where an exterior elliptic problem has to be solved in each time step. Second, a circular artificial boundary FR consisting of a circle of radius R is introduced, the original problem in an unbounded domain is transformed into the nonlocal boundary value problem in abounded subdomain. And the natural integral equation and the Poisson integral formula are obtained in the infinite domainΩ2 outside circle of radius R. The coupled variational formulation is given. Only the function itself, not its normal derivative at artificial boundary ΓR, appears in the variational equation, so that the unknown numbers are reducedand the boundary element stiffness matrix has a few different elements. Such a coupled method is superior to the one based on direct boundary element method. This paper discusses finite element discretization for variational problem and its corresponding numerical technique, and the convergence for the numerical solutions. Finally, the numerical example is presented to illustrate feasibility and efficiency of this method. 相似文献
24.
The physico-chemical properties and reactivity tested by hydrogen reduction have been studied for two series of NiO-ZnO mixed oxides of various composition. The solid nickel oxide or zinc oxide in interaction with the solution of nitrate of the second component were used as the precursors in each series. The differences in some physico-chemical parameters of the samples in both series were correlated with their reduction behaviour, followed both in iso- and non-isothermal regime. Moreower, the influence of various factors modifying the reactivity of mixed oxides was also investigated and the results were compared with those obtained from earlier studied analogous systems of quite different origin.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
25.
Hans C. Fogedby 《Journal of statistical physics》1992,69(1-2):411-425
We elaborate in some detail on a new phase space approach to complexity, due to Y.-C. Zhang. We show in particular that the connection between maximal complexity and power law noise or correlations can be derived from a simple variational principle. For a 1D signal we find 1/f noise, in accordance with Zhang. 相似文献
26.
Bernard Bialecki 《Numerical Algorithms》1994,8(2):167-184
Cyclic reduction and Fourier analysis-cyclic reduction (FACR) methods are presented for the solution of the linear systems which arise when orthogonal spline collocation with piecewise Hermite bicubics is applied to boundary value problems for certain separable partial differential equations on a rectangle. On anN×N uniform partition, the cyclic reduction and Fourier analysis-cyclic reduction methods requireO(N
2log2
N) andO(N
2log2log2
N) arithmetic operations, respectively. 相似文献
27.
Inhibition of the reduction of Cr(VI) at the magnetite–water interface by calcium carbonate coatings
The effect of calcium carbonate coatings on the reduction of aqueous chromate on the magnetite(1 1 1) surface has been investigated using a combination of synchrotron based X-ray photoemission spectroscopy (PES) and X-ray absorption near edge structure (XANES) spectroscopy, along with laboratory-based powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). CaCO3 coatings (dominantly calcite with minor quantities of aragonite and vaterite) of thicknesses ranging from 10 Å to 20 m were grown on magnetite(1 1 1) surfaces by exposure to supersaturated aqueous solutions followed by evaporation of the solution—a process that mimics pore-water evaporation in vadose zones leading to the formation of caliche and calcium carbonate coatings on mineral grains. Coating thicknesses were determined from attenuation of the Fe 2p photoemission signal by the carbonate coating. For coatings less than 15 Å thick, Cr 2p photoemission and Cr LII, LIII-edge XANES spectra show that chromate is reduced by the underlying magnetite surface; however, as the minimum coating thickness increases beyond 15 Å, the magnetite surface becomes passivated and further chromate reduction ceases. Our findings suggest that carbonate coatings on natural magnetite grains can significantly reduce or eliminate their ability to reduce Cr(VI), which is a toxic and highly mobile environmental contaminant. 相似文献
28.
Dailly A. Schneider R. Billaud D. Fort Y. Ghanbaja J. 《Journal of nanoparticle research》2003,5(3-4):389-393
A novel chemical reduction method using an activated alkaline hydride (LiH or NaH-t-BuONa) in tetrahydrofuran solvent has been applied to antimony salt reduction. X-ray diffraction and transmission electron microscopy studies have been carried out to characterize the morphology and structure of the materials. Alkali hydride nature influence has been proved. In both cases the process allows to prepare antimony particles in nanometer range from few nanometers to about 20nm which could be used as anodic materials for lithium–ion batteries. With lithium hydride well-crystallized particles inclined to agglomeration were observed whereas finely dispersed amorphous particles were pointing out after activated sodium hydride reduction. 相似文献
29.
M.C. Ubaldi V. Stasi U. Colombo D. Piccinin M. Martinelli 《Photonics and Nanostructures》2007,5(2-3):145-148
Roughness reduction of a submicron waveguide profile in chemically amplified negative resist is here performed by proper selection of an alkali-based developer, taking into account that its smaller molecules lead to smoother resist surface by altering the developing mechanism of aggregate extraction performed with standard quaternary ammonium hydroxide. Roughness is then analyzed by means of classical Atomic Force Microscope inspection; furthermore, a non-invasive line edge roughness analysis approach based on top-down scanning electron microscope acquisition gives comparable results, in terms of standard deviation and molecular aggregate periodicity. 相似文献
30.
“选择资费”的多重价格歧视特性 总被引:3,自引:0,他引:3
本文在分析电信业选择资费实例和价格结构的基础上 ,研究了选择资费中的三级和二级价格歧视 ,并提出了多重价格歧视的概念 .研究结果表明 ,电信公司在选择资费中综合运用了三级、二级价格歧视 ,且通过提供多个二部资费计费方案 ,达到双重二级价格歧视和优化二部资费的目的 .选择资费是电信公司应对市场竞争的一种定价策略 ,认识其经济特性有利于我国电信公司和电信管制部门进行科学决策 相似文献