全文获取类型
收费全文 | 362629篇 |
免费 | 4070篇 |
国内免费 | 1785篇 |
专业分类
化学 | 195263篇 |
晶体学 | 5775篇 |
力学 | 15157篇 |
综合类 | 64篇 |
数学 | 42215篇 |
物理学 | 110010篇 |
出版年
2020年 | 2923篇 |
2019年 | 3215篇 |
2018年 | 4151篇 |
2017年 | 4252篇 |
2016年 | 6330篇 |
2015年 | 4051篇 |
2014年 | 6221篇 |
2013年 | 15499篇 |
2012年 | 12383篇 |
2011年 | 14968篇 |
2010年 | 10720篇 |
2009年 | 10573篇 |
2008年 | 14168篇 |
2007年 | 14143篇 |
2006年 | 13376篇 |
2005年 | 12118篇 |
2004年 | 10982篇 |
2003年 | 9763篇 |
2002年 | 9606篇 |
2001年 | 10841篇 |
2000年 | 8195篇 |
1999年 | 6121篇 |
1998年 | 5144篇 |
1997年 | 5033篇 |
1996年 | 4862篇 |
1995年 | 4390篇 |
1994年 | 4441篇 |
1993年 | 4258篇 |
1992年 | 4740篇 |
1991年 | 4761篇 |
1990年 | 4544篇 |
1989年 | 4418篇 |
1988年 | 4338篇 |
1987年 | 4271篇 |
1986年 | 4165篇 |
1985年 | 5477篇 |
1984年 | 5600篇 |
1983年 | 4804篇 |
1982年 | 5119篇 |
1981年 | 4766篇 |
1980年 | 4536篇 |
1979年 | 4834篇 |
1978年 | 5053篇 |
1977年 | 5022篇 |
1976年 | 5079篇 |
1975年 | 4742篇 |
1974年 | 4826篇 |
1973年 | 5024篇 |
1972年 | 3683篇 |
1971年 | 2960篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
G. L. Litvinov 《Journal of Mathematical Sciences》1987,38(2):1734-1761
992.
993.
A fully coupled formulation combining reactive transport and an existing thermo-hydro-mechanical (THM) code is presented.
Special attention has been given to phenomena likely to be encountered in clay barriers used as part of containment systems
of nuclear waste. The types of processes considered include hydrolysis, complex formation, oxidation/reduction reactions,
acid/base reactions, precipitation/dissolution of minerals and cation exchange. Both kinetically-controlled and equilibrium-controlled
reactions have been incorporated. The total analytical concentrations (including precipitated minerals) are adopted as basic
transport variables and chemical equilibrium is achieved by minimizing Gibbs Free Energy. The formulation has been incorporated
in a general purpose computer code capable of performing numerical analysis of engineering problems. A validation exercise
concerning a laboratory experiment involving the heating and hydration of an expansive compacted clay is described. 相似文献
994.
J. Mass M. Avella J. Jimnez M. Callahan E. Grant K. Rakes D. Bliss B. Wang 《Superlattices and Microstructures》2007,42(1-6):306
Understanding the luminescence of ZnO is very important for some applications. In spite of the many studies carried out, there are still some points concerning the origin of some of the luminescence emissions in ZnO crystals that require additional study; in particular, the role of extended defects remains to be a matter of controversy. We present here a cathodoluminescence analysis of the defects generated by Vickers indentation in hydrothermal HTT crystals. Special emphasis was paid to the luminescence band peaking around 3.3 eV. The origin of this band is a matter of controversy, since it has been related to different causes, extended defects being one of the candidates for this emission. The CL images were acquired around crystal defects. It is observed that the 3.3 eV emission is enhanced around the crystal defects; though it is also observed, but weaker, out of the defect regions, which suggests that there exist two luminescence emissions peaking very close to 3.3 eV. The two emissions, one related to structural defects and the other to the LO phonon replica of the free excitonic band, appear very close each other and their relative intensity should determine the shape of the spectrum. 相似文献
995.
Using the concept of a twisted trace density on a cyclic groupoid, a trace is constructed on a formal deformation quantization of a symplectic orbifold. An algebraic index theorem for orbifolds follows as a consequence of a local Riemann-Roch theorem for such densities. In the case of a reduced orbifold, this proves a conjecture by Fedosov, Schulze, and Tarkhanov. Finally, it is shown how the Kawasaki index theorem for elliptic operators on orbifolds follows from this algebraic index theorem. 相似文献
996.
The behaviour of the amplitude-frequency characteristics of families of periodic solutions, produced from the equilibrium position of a system, is established by a qualitative investigation of the equation of the oscillations of a pendulum, the length of which is an arbitrary periodic function of time. The non-local conditions for their stability and instability, expressed in terms of the amplitude and frequency of the oscillations, are obtained. The results are used when discussing the parametric and self-excited oscillatory model of a swing. In the parametric model the length of a swing is a specified periodic function of time, and in the self-excited oscillatory model it is a function of the phase coordinates of the system. For an appropriate choice of these functions, both systems have a common periodic solution. It is shown that the parametric model leads to an erroneous conclusion regarding the instability of the periodic mode, which is in fact realized in the oscillations of a swing, whereas the self-excited oscillatory model indicates its stability. 相似文献
997.
A. S. Boreysho S. L. Druzhinin V. M. Malkov I. A. Kiselev A. V. Morozov A. E. Orlov A. V. Savin I. V. Shatalov V. I. Zapryagaev A. V. Sobolev 《Thermophysics and Aeromechanics》2007,14(4):561-576
The matter of development of a high-performance pressure recovery system (PRS) for a high-power HF/DF laser is discussed.
A sequence of design steps is proposed, which involves estimation of basic characteristics of PRS components with the help
of one-dimensional integral and semi-empirical procedures; simulation, to be performed using three-dimensional non-stationary
Navier — Stokes equations; experimental modelling aimed at verification of the calculation procedures and at refinement of
obtained parameters; and a fullscale experiment. An ejector-type system providing for recovery of pressure from 12 Torr to
atmospheric pressure in the gas-dynamic system of an HF/DF laser of several-tens-kilowatt power is developed. Matching conditions
for parameters of individual PRS components as well as joint functioning of the PRS with a continuous chemical laser in an
integral complex are analysed. Conditions for minimization of mass-dimensional characteristics of the laser-PRS complex necessary
for the development of ground-based mobile systems are identified. 相似文献
998.
K.T.A.L. Burm 《等离子体物理论文集》2007,47(6):458-464
The discharge behaviour of an atmospheric dielectric barrier parallel plate discharge, used for surface treatment, is studied. Since an uniform plasma is preferable for surface treatment, filaments must be avoided in the discharge. The occurrence of filaments can be detected by measuring the current flowing through the discharge. Current and voltage measurements give an indication of the power consumption by the plasma. The power consumption of the plasma as function of the applied frequency is examined. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
999.
In single-objective optimization it is possible to find a global optimum, while in the multi-objective case no optimal solution is clearly defined, but several that simultaneously optimize all the objectives. However, the majority of this kind of problems cannot be solved exactly as they have very large and highly complex search spaces. Recently, meta-heuristic approaches have become important tools for solving multi-objective problems encountered in industry as well as in the theoretical field. Most of these meta-heuristics use a population of solutions, and hence the runtime increases when the population size grows. An interesting way to overcome this problem is to apply parallel processing. This paper analyzes the performance of several parallel paradigms in the context of population-based multi-objective meta-heuristics. In particular, we evaluate four alternative parallelizations of the Pareto simulated annealing algorithm, in terms of quality of the solutions, and speedup. 相似文献
1000.
We investigated that the effect of the number of segregated Li atoms on the rate of oxidation on a LiAl alloy surface. Oxygen molecules adsorbed on the LiAl alloy react with the surface atoms to form stable oxides. The segregated Li atoms at reconstructed surfaces (c(2×2) and (2×1)) enhance the oxidation rate and form stable LiAlOx and Li2O. The degree of enhancement of oxidation by segregated Li atoms varies as a function of O2 exposure and annealing temperature, where the latter is directly related to the mode of surface reconstruction by Li segregation. 相似文献