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   1974篇
  免费   192篇
  国内免费   199篇
化学   84篇
晶体学   1篇
力学   187篇
综合类   50篇
数学   1760篇
物理学   283篇
  2023年   19篇
  2022年   12篇
  2021年   29篇
  2020年   49篇
  2019年   55篇
  2018年   48篇
  2017年   49篇
  2016年   53篇
  2015年   40篇
  2014年   77篇
  2013年   128篇
  2012年   76篇
  2011年   91篇
  2010年   85篇
  2009年   110篇
  2008年   147篇
  2007年   130篇
  2006年   147篇
  2005年   107篇
  2004年   86篇
  2003年   103篇
  2002年   106篇
  2001年   85篇
  2000年   82篇
  1999年   76篇
  1998年   76篇
  1997年   51篇
  1996年   49篇
  1995年   35篇
  1994年   22篇
  1993年   14篇
  1992年   17篇
  1991年   23篇
  1990年   11篇
  1989年   10篇
  1988年   3篇
  1987年   5篇
  1986年   7篇
  1985年   12篇
  1984年   6篇
  1983年   6篇
  1982年   6篇
  1981年   4篇
  1980年   4篇
  1979年   6篇
  1978年   2篇
  1977年   3篇
  1975年   1篇
  1970年   1篇
  1936年   1篇
排序方式: 共有2365条查询结果,搜索用时 15 毫秒
1.
In this paper, the problem of the uniform stability for a class of fuzzy fractional-order genetic regulatory networks with random discrete delays, distributed delays, and parameter uncertainties is studied. Although there is a portion of literature on using fixed point theorems to study the stability of fractional neural networks, most of them required the fractional order to be in 1 2 , 1 . However, the case of the fractional-order belonging to ( 0 , 1 2 ) has not been discussed. To solve it, this work proposes a novel idea of using fixed point theory to study the stability of fuzzy (0,1) order neural networks, the problem of the uniqueness of the solution of the considered genetic regulatory networks is resolved, and a novel sufficient condition to guarantee the uniform stability of above genetic regulatory networks is also derived. Eventually, an example is given to demonstrate that the obtained result is effective.  相似文献   
2.
《Mathematische Nachrichten》2018,291(10):1514-1532
Necessary and sufficient conditions for uniform rotundity of Orlicz function spaces equipped with the p‐Amemiya norm are presented. The obtained results unify, complete and widen the characterization of uniform rotundity of Orlicz spaces. In the case of the ∞‐Amemiya (i.e. the Luxemburg) norm or the 1‐Amemiya (i.e. the Orlicz) norm, these results were known earlier. Some connections with the fixed point theory and the best approximation theory are presented.  相似文献   
3.
In this paper we study the domain of the generator of stable processes, stable-like processes and more general pseudo- and integro-differential operators which naturally arise both in analysis and as infinitesimal generators of Lévy- and Lévy-type (Feller) processes. In particular we obtain conditions on the symbol of the operator ensuring that certain (variable order) Hölder and Hölder–Zygmund spaces are in the domain. We use tools from probability theory to investigate the small-time asymptotics of the generalized moments of a Lévy or Lévy-type process (Xt)t0,
limt0?1t(Exf(Xt)?f(x)),xRd,
for functions f which are not necessarily bounded or differentiable. The pointwise limit exists for fixed xRd if f satisfies a Hölder condition at x. Moreover, we give sufficient conditions which ensure that the limit exists uniformly in the space of continuous functions vanishing at infinity. As an application we prove that the domain of the generator of (Xt)t0 contains certain Hölder spaces of variable order. Our results apply, in particular, to stable-like processes, relativistic stable-like processes, solutions of Lévy-driven SDEs and Lévy processes.  相似文献   
4.
This paper studies the Hankel determinants generated by a discontinuous Gaussian weight with one and two jumps. It is an extension in a previous study, in which they studied the discontinuous Gaussian weight with a single jump. By using the ladder operator approach, we obtain a series of difference and differential equations to describe the Hankel determinant for the single jump case. These equations include the Chazy II equation, continuous and discrete Painlevé IV. In addition, we consider the large n behavior of the corresponding orthogonal polynomials and prove that they satisfy the biconfluent Heun equation. We also consider the jump at the edge under a double scaling, from which a Painlevé XXXIV appeared. Furthermore, we study the Gaussian weight with two jumps and show that a quantity related to the Hankel determinant satisfies a two variables' generalization of the Jimbo‐Miwa‐Okamoto σ‐form of the Painlevé IV.  相似文献   
5.
The objective of this paper is to construct and analyze a fitted operator finite difference method (FOFDM) for the family of time‐dependent singularly perturbed parabolic convection–diffusion problems. The solution to the problems we consider exhibits an interior layer due to the presence of a turning point. We first establish sharp bounds on the solution and its derivatives. Then, we discretize the time variable using the classical Euler method. This results in a system of singularly perturbed interior layer two‐point boundary value problems. We propose a FOFDM to solve the system above. Through a rigorous error analysis, we show that the scheme is uniformly convergent of order one with respect to both time and space variables. Moreover, we apply Richardson extrapolation to enhance the accuracy and the order of convergence of the proposed scheme. Numerical investigations are carried out to demonstrate the efficacy and robustness of the scheme.  相似文献   
6.
数n的汉明重量是指n的二进制字符串表达式中数字1的个数,用Ham(n)来表示.低汉明重量序列在密码系统和编码理论中有非常广泛的应用.本文建立了低汉明重量数的序列表达式,并且利用指数和的上界以及Erdos-Turan不等式证明低汉明重量序列的均匀分布性质,从而确保密码算法的随机性和运算效率.  相似文献   
7.
罗明  李增禄 《运筹与管理》2021,30(8):175-180
研究了供应商歧视定价时网络零售商店内推介策略。首先,以供应商统一定价模型为基准,通过逆推归纳法求解不同推介策略组合下零售商和供应商的均衡利润,研究发现:仅当消费者对两家零售商认知差异较小时四种推介策略组合才能同时成立,且随着推介费用的增大两零售商均衡推介策略依次为:都不推介、仅强势零售商1推介和双向推介。其次,构建供应商歧视定价模型,发现歧视定价有利于弱势零售商2获得市场空间,随着消费者对两家零售商感知差异和推介费用的变化呈现出多样化的均衡推介策略。最后,探讨了两种定价模型下供应商的最优利润,发现受推介策略的影响歧视定价未必能够为供应商带来更多利润。  相似文献   
8.
9.
In this paper we consider the long-time asymptotics of a linear version of the Smoluchowski equation which describes the evolution of a tagged particle moving in a random distribution of fixed particles. The volumes v of these particles are independently distributed according to a probability distribution which decays asymptotically as a power law v?σ. The validity of the equation has been rigorously proved in [22] taking as a starting point a particle model and for values of the exponent σ>3, but the model can be expected to be valid, on heuristic grounds, for σ>53. The resulting equation is a non-local linear degenerate parabolic equation. The solutions of this equation display a rich structure of different asymptotic behaviors according to the different values of the exponent σ. Here we show that for 53<σ<2 the linear Smoluchowski equation is well-posed and that there exists a unique self-similar profile which is asymptotically stable.  相似文献   
10.
Controllable synthesis of atomically ordered intermetallic nanoparticles (NPs) is crucial to obtain superior electrocatalytic performance for fuel cell reactions, but still remains arduous. Herein, we demonstrate a novel and general hydrogel‐freeze drying strategy for the synthesis of reduced graphene oxide (rGO) supported Pt3M (M=Mn, Cr, Fe, Co, etc.) intermetallic NPs (Pt3M/rGO‐HF) with ultrasmall particle size (about 3 nm) and dramatic monodispersity. The formation of hydrogel prevents the aggregation of graphene oxide and significantly promotes their excellent dispersion, while a freeze‐drying can retain the hydrogel derived three‐dimensionally (3D) porous structure and immobilize the metal precursors with defined atomic ratio on GO support during solvent sublimation, which is not afforded by traditional oven drying. The subsequent annealing process produces rGO supported ultrasmall ordered Pt3M intermetallic NPs (≈3 nm) due to confinement effect of 3D porous structure. Such Pt3M intermetallic NPs exhibit the smallest particle size among the reported ordered Pt‐based intermetallic catalysts. A detailed study of the synthesis of ordered intermetallic Pt3Mn/rGO catalyst is provided as an example of a generally applicable method. This study provides an economical and scalable route for the controlled synthesis of Pt‐based intermetallic catalysts, which can pave a way for the commercialization of fuel cell technologies.  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