全文获取类型
收费全文 | 270258篇 |
免费 | 2238篇 |
国内免费 | 987篇 |
专业分类
化学 | 130935篇 |
晶体学 | 4021篇 |
力学 | 14347篇 |
综合类 | 4篇 |
数学 | 49527篇 |
物理学 | 74649篇 |
出版年
2018年 | 11471篇 |
2017年 | 11240篇 |
2016年 | 8195篇 |
2015年 | 2491篇 |
2014年 | 2655篇 |
2013年 | 8087篇 |
2012年 | 8858篇 |
2011年 | 16775篇 |
2010年 | 9885篇 |
2009年 | 10192篇 |
2008年 | 12340篇 |
2007年 | 14601篇 |
2006年 | 6098篇 |
2005年 | 6657篇 |
2004年 | 6413篇 |
2003年 | 6309篇 |
2002年 | 5242篇 |
2001年 | 6001篇 |
2000年 | 4646篇 |
1999年 | 3644篇 |
1998年 | 2912篇 |
1997年 | 2905篇 |
1996年 | 2912篇 |
1995年 | 2628篇 |
1994年 | 2465篇 |
1993年 | 2380篇 |
1992年 | 2837篇 |
1991年 | 2721篇 |
1990年 | 2659篇 |
1989年 | 2698篇 |
1988年 | 2635篇 |
1987年 | 2643篇 |
1986年 | 2456篇 |
1985年 | 3315篇 |
1984年 | 3321篇 |
1983年 | 2749篇 |
1982年 | 2950篇 |
1981年 | 2881篇 |
1980年 | 2797篇 |
1979年 | 2936篇 |
1978年 | 3171篇 |
1977年 | 2978篇 |
1976年 | 2908篇 |
1975年 | 2767篇 |
1974年 | 2711篇 |
1973年 | 2739篇 |
1972年 | 1776篇 |
1968年 | 1939篇 |
1967年 | 2140篇 |
1966年 | 1937篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Parallel discrete event simulation (PDES) is concerned with the distributed execution of large-scale system models on multiple processors. It is an enabler in the implementation of the virtual enterprise concept, integrating semi-autonomous models of production cells, factories, or units of a supply chain. The key issue in PDES is to maintain causality relationships between system events, while maximizing parallelism in their execution. Events can be executed conservatively only when it is safe to do so, sacrificing the extent to which potential parallelism of the system can be exploited. Alternatively, they can be processed optimistically without guarantee of correctness, but incurring the overhead of a rollback to an earlier saved state when causality error is detected. The paper proposes a modified optimistic scheme for distributed simulation of constituent models of a supply chain in manufacturing, which exploits the inherent operating characteristics of its domain. 相似文献
992.
Al-Cu-Fe thin films were prepared by laser induced arc (laser-arc) method from a single source—Al63Cu25Fe12 alloy, which was proved to consist of quasicrystalline phase together with approximant phase. The composition of the deposited films meets the requirement for formation of icosahedral symmetry phase. Quasicrystalline phase was obtained after annealing the amorphous as-deposit film samples. The optical properties of the samples were investigated. Thin film samples of Al, Cu and Fe deposited under the same condition were employed for comparison. The results showed specific reflective properties of Al-Cu-Fe quasicrystal thin film in some wavelength range. The optical conductivity of the films exhibited a negative peak, centered about 440 nm in range of 190 to 800 nm. The Al-Cu-Fe quasicrystal thin films could absorb almost all the ray in the wavelength range from 420nm to 450 nm. The ratio of absorption was greater than 99%. 相似文献
993.
Heinz H. Bauschke Patrick L. Combettes 《Proceedings of the American Mathematical Society》2003,131(12):3757-3766
An iterative method is proposed to construct the Bregman projection of a point onto a countable intersection of closed convex sets in a reflexive Banach space.
994.
By means of a new force sensor based on optical beam deflection (OBD), the mechanical effects of laser-matter interaction underwater at different incident laser energy are investigated in detail. The experimental results show that a target underwater is impacted in turn by laser-plasma ablation force and high-speed liquid-jet impulse induced by bubbles collapse in the vicinity of a solid boundary. Furthermore, the amplitudes of the two forces increase monotonously with laser energy. According to the ablation force detected by the experiment and the theoretical relationship between laser intensity and ablation pressure, the value of liquid-jet impact against a solid boundary can be easily obtained. In addition, based on the model of a collapsing bubble, some characteristic parameters, such as the liquid-jet impact velocity, the maximum bubble radius, the bubble energy can also be obtained at different laser energy, which are valuable in the corresponding research fields. 相似文献
995.
The historical Ehrenfest model dating back to 1907 describes the process of equilibration together with fluctuations around the thermal equilibrium. This approach represents a special case in the dynamics of N uncoupled two-state systems. In this article we present a generalization of the original model by introducing an additional parameter p which denotes the probability of a single state change. Analytical solutions for the probability distribution of the system's state as well as the fluctuation distribution are derived. Interestingly, close inspection of the fluctuation distribution reveals an intrinsic time scale. Sampling the system's state at much slower rates yields the familiar macroscopic exponential distribution for equilibrium processes. For faster measurements a power law extends roughly over log10 N orders of magnitude followed by an exponential tail. At some point, further increases of the sampling rate merely result in a shift of the fluctuation distribution towards higher values leaving plateau at small fluctuation sizes behind. Since the generic solution is rather unwieldy, we derive and discuss simple and intuitive analytical solutions in the limit of small p and large N. Furthermore, we relax the quantization of time by considering a complementary approach in continuous time. Finally we demonstrate that the fluctuation distributions resulting from the two different approaches bear identical characteristic features. 相似文献
996.
H. Petersson 《Acta Mathematica Hungarica》2003,100(1-2):69-81
The PDE-preserving operators O on the space of nuclearly entire functions of bounded type HNb(E) on a Banach space E are characterized. An operator is PDE-preserving when it preserves homogenous solutions to homogeneous convolution equations.
We establish a one to one correspondence between O and a set Σ of sequences of entire functionals, i.e. exponential type functions. In this way, algebraic structures on Σ,
such as ring structures, can be carried over to O and vice versa. In particular, it follows that O is a non-commutative ring (algebra) with unity with respect to composition and the convolution operators form a commutative
subring (subalgebra). We discuss range and kernel properties, for the operators in O, and characterize the projectors (onto polynomial spaces) in O by determining the corresponding elements in Σ.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
997.
We give a purely algebro-geometric proof of the fact that every nonsingular
projective curve can be defined over a finite extension of its moduli field.
This extends a result byWolfart [7] to curves over fields of arbitrary
characteristic.
Received: 30 November 2001 相似文献
998.
We propose a minimum mean absolute error linear interpolator (MMAELI), based on theL
1 approach. A linear functional of the observed time series due to non-normal innovations is derived. The solution equation
for the coefficients of this linear functional is established in terms of the innovation series. It is found that information
implied in the innovation series is useful for the interpolation of missing values. The MMAELIs of the AR(1) model with innovations
following mixed normal andt distributions are studied in detail. The MMAELI also approximates the minimum mean squared error linear interpolator (MMSELI)
well in mean squared error but outperforms the MMSELI in mean absolute error. An application to a real series is presented.
Extensions to the general ARMA model and other time series models are discussed.
This research was supported by a CityU Research Grant and Natural Science Foundation of China. 相似文献
999.
1000.
Ben Morris 《Probability Theory and Related Fields》2003,125(2):259-265
We show that a.s. all of the connected components of the Wired Spanning Forest are recurrent, proving a conjecture of Benjamini,
Lyons, Peres and Schramm. Our analysis relies on a simple martingale involving the effective conductance between the endpoints
of an edge in a uniform spanning tree. We believe that this martingale is of independent interest and will find further applications
in the study of uniform spanning trees and forests.
Received: 20 April 2001 / Revised version: 23 July 2002 / Published online: 14 November 相似文献