全文获取类型
收费全文 | 11216篇 |
免费 | 426篇 |
国内免费 | 62篇 |
专业分类
化学 | 8209篇 |
晶体学 | 84篇 |
力学 | 236篇 |
数学 | 1351篇 |
物理学 | 1824篇 |
出版年
2023年 | 72篇 |
2022年 | 89篇 |
2021年 | 128篇 |
2020年 | 208篇 |
2019年 | 170篇 |
2018年 | 134篇 |
2017年 | 117篇 |
2016年 | 272篇 |
2015年 | 259篇 |
2014年 | 288篇 |
2013年 | 523篇 |
2012年 | 768篇 |
2011年 | 953篇 |
2010年 | 452篇 |
2009年 | 300篇 |
2008年 | 706篇 |
2007年 | 763篇 |
2006年 | 800篇 |
2005年 | 795篇 |
2004年 | 620篇 |
2003年 | 527篇 |
2002年 | 456篇 |
2001年 | 131篇 |
2000年 | 121篇 |
1999年 | 117篇 |
1998年 | 96篇 |
1997年 | 107篇 |
1996年 | 129篇 |
1995年 | 98篇 |
1994年 | 107篇 |
1993年 | 91篇 |
1992年 | 97篇 |
1991年 | 78篇 |
1990年 | 73篇 |
1989年 | 58篇 |
1988年 | 70篇 |
1987年 | 49篇 |
1986年 | 37篇 |
1985年 | 107篇 |
1984年 | 61篇 |
1983年 | 45篇 |
1982年 | 65篇 |
1981年 | 73篇 |
1980年 | 55篇 |
1979年 | 54篇 |
1978年 | 45篇 |
1977年 | 49篇 |
1976年 | 45篇 |
1975年 | 42篇 |
1974年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
F. Sibel Salman Jayant R. Kalagnanam Sesh Murthy Andrew Davenport 《Journal of Heuristics》2002,8(2):215-239
For hard optimization problems, it is difficult to design heuristic algorithms which exhibit uniformly superior performance for all problem instances. As a result it becomes necessary to tailor the algorithms based on the problem instance. In this paper, we introduce the use of a cooperative problem solving team of heuristics that evolves algorithms for a given problem instance. The efficacy of this method is examined by solving six difficult instances of a bicriteria sparse multiple knapsack problem. Results indicate that such tailored algorithms uniformly improve solutions as compared to using predesigned heuristic algorithms. 相似文献
32.
A current interpretation of XPS spectra of Ni metal assumes that the main 6 eV satellite is due to a two hole c3d94s2 (c is a core hole) final state effect. We report REELS observation in AES at low voltages of losses (plasmons and inter-band transitions) corresponding to the satellite structures in Ni metal 2p spectra. The satellite near 6 eV is attributed to a predominant surface plasmon loss. A current interpretation of Ni 2p spectra of oxides and other compounds is based on charge transfer assignments of the main peak at 854.6 eV and the broad satellite centred at around 861 eV to the cd9L and the unscreened cd8 final-state configurations, respectively (L is a ligand hole). Multiplet splittings have been shown to be necessary for assignment of Fe 2p and Cr 2p spectral profiles and chemical states. The assignments of Ni 2p states are re-examined with intra-atomic multiplet envelopes applied to Ni(OH)2, NiOOH and NiO spectra. It is shown that the free ion multiplet envelopes for Ni2+ and Ni3+ simulate the main line and satellite structures for Ni(OH)2 and NiOOH. Fitting the NiO Ni 2p spectral profile is not as straightforward as the hydroxide and oxyhydroxide. It may involve contributions from inter-atomic, non-local electronic coupling and screening effects with multiplet structures significantly different from the free ions as found for MnO. A scheme for fitting these spectra using multiplet envelopes is proposed. 相似文献
33.
P. F. Mantica Jr. B. D. Kern B. E. Zimmerman W. B. Walters J. Rikovska N. J. Stone 《Hyperfine Interactions》1992,75(1-4):415-421
The performance of two external plastic scintillator detectors has been tested in an off-line mode using a source of106RuFe at UNISOR/NOF. The measurement of beta asymmetries at various temperatures has resulted in the reproduction of the previously-determined
magnetic dipole moment for the 1+ ground state of106Rh and in addition the conclusion that the sign of this moment is positive. 相似文献
34.
We give a small functorial algebraic model for the 2-stage Postnikov section of the K-theory spectrum of a Waldhausen category and use our presentation to describe the multiplicative structure with respect to biexact functors. 相似文献
35.
The authors introduce a new concept of measure-valued solution for the 3-D incompressible Euler equations in order to incorporate the complex phenomena present in limits of approximate solutions of these equations. One application of the concepts developed here is the following important result: a sequence of Leray-Hopf weak solutions of the Navier-Stokes equations converges in the high Reynolds number limit to a measure-valued solution of 3-D Euler defined for all positive times. The authors present several explicit examples of solution sequences for 3-D incompressible Euler with uniformly bounded local kinetic energy which exhibit complex phenomena involving both persistence of oscillations and development of concentrations. An extensions of the concept of Young measure is developed to incorporate these complex phenomena in the measure-valued solutions constructed here.Partially supported by N.S.F. GrantPartially supported by N.S.F. Grant 84-0223 and 86-11110 相似文献
36.
Summary There has been a rapid growth of interest in techniques for site-directed drug design, fuelled by the increasing availability of structural models of proteins of therapeutic importance, and by studies reported in the literature showing that potent chemical leads can be obtained by these techniques. Structure generation programs offer the prospect of discovering highly original lead structures from novel chemical families. Due to the fact that this technique is more-or-less still in its infancy, there are no case studies available that demonstrate the use of structure generation programs for site-directed drug design. Such programs were first proposed in 1986, and became commercially available in early 1992. They have shown their ability to reproduce, or suggest reasonable alternatives for, ligands in well-defined binding sites. This brief review will discuss the recent advances that have been made in the field of site-directed structure generation. 相似文献
37.
38.
Summary. We examine the convergence characteristics of iterative methods based on a new preconditioning operator for solving the linear
systems arising from discretization and linearization of the steady-state Navier-Stokes equations. With a combination of analytic
and empirical results, we study the effects of fundamental parameters on convergence. We demonstrate that the preconditioned
problem has an eigenvalue distribution consisting of a tightly clustered set together with a small number of outliers. The
structure of these distributions is independent of the discretization mesh size, but the cardinality of the set of outliers
increases slowly as the viscosity becomes smaller. These characteristics are directly correlated with the convergence properties
of iterative solvers.
Received August 5, 2000 / Published online June 20, 2001 相似文献
39.
Lisa Higham David Kirkpatrick Karl Abrahamson Andrew Adler 《Journal of Algorithms in Cognition, Informatics and Logic》1997,23(2):291-328
Probabilistic algorithms are developed for a basic problem in distributed computation, assuming anonymous, asynchronous, unidirectional rings of processors. The problem, known as Solitude Detection, requires that a nonempty subset of the processors, calledcontenders, determine whether or not there is exactly one contender. Monte Carlo algorithms are developed that err with probability bounded by a specified parameter and exhibit either message or processor termination. The algorithms transmit an optimal expected number of bits, to within a constant factor. Their bit complexities display a surprisingly rich dependence on the kind of termination exhibited and on the processors' knowledge of the size of the ring. Two probabilistic tools are isolated and then combined in various ways to achieve all our algorithms. 相似文献
40.
In the study of integrable systems of ODE's arising from a Lax pair with a parameter, the constants of the motion occur as spectral curves. The specific curves depend upon the representation of the Lie algebra. In this paper a Galois theory of spectral curves is given that classifies the spectral curves from an integrable system. The spectral curves correspond to conjugacy classes of certain subgroups of the Weyl group for the Lie algebra. The theory is illustrated with the periodic Toda lattice.Partially supported by a Louisiana Education Quality Support Fund grant LEQSF (87-89)-RD-A-8 相似文献