首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1994篇
  免费   255篇
  国内免费   195篇
化学   95篇
晶体学   5篇
力学   125篇
综合类   48篇
数学   1867篇
物理学   304篇
  2024年   9篇
  2023年   24篇
  2022年   35篇
  2021年   45篇
  2020年   56篇
  2019年   52篇
  2018年   56篇
  2017年   89篇
  2016年   93篇
  2015年   41篇
  2014年   93篇
  2013年   174篇
  2012年   107篇
  2011年   121篇
  2010年   93篇
  2009年   132篇
  2008年   119篇
  2007年   104篇
  2006年   129篇
  2005年   97篇
  2004年   73篇
  2003年   84篇
  2002年   96篇
  2001年   73篇
  2000年   62篇
  1999年   52篇
  1998年   50篇
  1997年   38篇
  1996年   21篇
  1995年   25篇
  1994年   34篇
  1993年   21篇
  1992年   10篇
  1991年   15篇
  1990年   14篇
  1989年   11篇
  1988年   10篇
  1987年   11篇
  1986年   7篇
  1985年   18篇
  1984年   12篇
  1983年   3篇
  1982年   9篇
  1981年   6篇
  1979年   2篇
  1978年   4篇
  1977年   5篇
  1976年   3篇
  1975年   2篇
  1936年   3篇
排序方式: 共有2444条查询结果,搜索用时 9 毫秒
31.
In this paper, an unstable linear time invariant (LTI) ODE system is stabilized exponentially by the PDE compensato—a wave equation with Kelvin‐Voigt (K‐V) damping. Direct feedback connections between the ODE system and wave equation are established: The velocity of the wave equation enters the ODE through the variable vt(1,t); meanwhile, the output of the ODE is fluxed into the wave equation. It is found that the spectrum of the system operator is composed of two parts: point spectrum and continuous spectrum. The continuous spectrum consists of an isolated point , and there are two branches of asymptotic eigenvalues: the first branch approaches to , and the other branch tends to ?. It is shown that there is a sequence of generalized eigenfunctions, which forms a Riesz basis for the Hilbert state space. As a consequence, the spectrum‐determined growth condition and exponential stability of the system are concluded.  相似文献   
32.
We consider fourth‐order singularly perturbed problems posed on smooth domains and the approximation of their solution by a mixed Finite Element Method on the so‐called Spectral Boundary Layer Mesh. We show that the method converges uniformly, with respect to the singular perturbation parameter, at an exponential rate when the error is measured in the energy norm. Numerical examples illustrate our theoretical findings.  相似文献   
33.
A new family of univariate exponential slash distribution is introduced, which is based on elliptical distributions and defined by means of a stochastic representation as the scale mixture of an elliptically distributed random variable with respect to the power of an exponential random variable. The same idea is extended to the multivariate case. General properties of the resulting families, including their moments and kurtosis coefficient, are studied. And inferences based on methods of moment and maximum likelihood are discussed. A real data is presented to show this family is flexible and fits much better than other related families.  相似文献   
34.
A new non-iterative curve resolution technique for resolving single decay profiles is proposed. The new technique, called DoubleSlicing, is based on the Decra (Direct Exponential Curve Resolution Algorithm) principle. While the original Decra was designed to resolve several decay curves simultaneously and thus fitting common pure exponentials, DoubleSlicing can resolve single decay profiles by a simple double data transformation followed by an analytical and unique three-way decomposition. The new approach is successfully demonstrated on experimental NMR CPMG relaxation data, measured on combinations of unmixed paramagnetic CuSO(4) solutions. Decay signals of the water component were acquired following an innovative experimental design that ensured no interaction between the components present in each sample under observation. DoubleSlicing proved to be accurate in estimating relaxation times differing in one order of magnitude (range: 19.6-159.4ms). Its performance was comparable to discrete exponential fitting with the advantage of being much faster - in terms of computation time, DoubleSlicing outperformed exponential fitting by a factor of four.  相似文献   
35.
夏文华 《大学数学》2006,22(6):33-37
对一类具时滞的Hopfeild型神经网络模型,在非线性神经元激励函数只要求满足Lipschitz连续的条件下,利用推广的Halanay时延微分析不等式、Dini导数以及泛函微分析技术,给出了这类模型的平衡点全局指数稳定性和全局吸引性的充分条件,这些条件易于检验,且改进和推广了前人的结论.此外,此文给出了研究神经网络模型的全局吸引性的微分不等式比较方法.  相似文献   
36.
Aptamers which specifically recognize targets are selected from random oligonucleotide library using systematic evolution of ligands by exponential enrichment (SELEX). In this paper, capillary electrophoresis (CE) as a separation approach has been introduced to SELEX procedure. The high efficiency of CE gives rise to greatly shorten the selection procedure. The results from enzyme-linked assay and dot blot experiment show that an enrichment pool has been obtained after four rounds selection, which can specifically recognize ricin. __________ Translated from Chemical Journal of Chinese Universities, 2006, 27(10): 1,840–1,843 [译自: 高等学校化学学报]  相似文献   
37.
ON THE ASYMPTOTIC BEHAVIOR OF HOPFIELD NEURAL NETWORK WITH PERIODIC INPUTS   总被引:3,自引:0,他引:3  
IntroductionSincethespecialsuperiorityofartificialneuralnetworkstechnologyinvariousengineeringtechniquesfields,suchasoptimization ,associativememories,patternrecognition ,signalprocessingandautomaticcontrol,therehasbeenincreasinginterestintheinvestigati…  相似文献   
38.
研究一类变时滞BAM神经网络平衡点的全局指数稳定性问题.在不要求激励函数全局Lipschitz条件下,通过构造合适的Lyapunov泛函,并结合Young不等式,得到了BAM神经网络模型在一定条件下全局指数稳定的一些充分条件,推广和改进了前人的相关结论,为综合设计指数稳定的时滞BAM神经网络提供了依据.  相似文献   
39.
This paper is concerned with interval general bidirectional associative memory (BAM) neural networks with proportional delays. Using appropriate nonlinear variable transformations, the interval general BAM neural networks with proportional delays can be equivalently transformed into the interval general BAM neural networks with constant delays. The sufficient condition for the existence and uniqueness of equilibrium point of the model is established by applying Brouwer's fixed point theorem. By constructing suitable delay differential inequalities, some sufficient conditions for the global exponential stability of the model are obtained. Two examples are given to illustrate the effectiveness of the obtained results. This paper ends with a brief conclusion. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   
40.
In this study, we introduce newly defined Gamma operators which preserve constants and e2μ·, μ>0 functions. In accordance with this purpose, we focus on their approximation properties such as uniform convergence, rate of convergence, asymptotic formula, and saturation results. Superior properties of introduced operators have been tested both theoretically and numerically in certain senses to highlight the performance of the new constructions of Gamma operators.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号