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   24511篇
  免费   3661篇
  国内免费   2239篇
化学   7999篇
晶体学   154篇
力学   2764篇
综合类   558篇
数学   9715篇
物理学   9221篇
  2024年   50篇
  2023年   612篇
  2022年   485篇
  2021年   627篇
  2020年   659篇
  2019年   598篇
  2018年   580篇
  2017年   843篇
  2016年   977篇
  2015年   790篇
  2014年   1335篇
  2013年   1665篇
  2012年   1340篇
  2011年   1509篇
  2010年   1356篇
  2009年   1534篇
  2008年   1670篇
  2007年   1777篇
  2006年   1470篇
  2005年   1326篇
  2004年   1260篇
  2003年   1032篇
  2002年   967篇
  2001年   815篇
  2000年   686篇
  1999年   652篇
  1998年   570篇
  1997年   497篇
  1996年   443篇
  1995年   418篇
  1994年   274篇
  1993年   256篇
  1992年   190篇
  1991年   219篇
  1990年   151篇
  1989年   99篇
  1988年   142篇
  1987年   84篇
  1986年   73篇
  1985年   69篇
  1984年   53篇
  1983年   33篇
  1982年   36篇
  1981年   45篇
  1980年   31篇
  1979年   33篇
  1978年   21篇
  1977年   13篇
  1976年   11篇
  1974年   9篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
郑海龙 《应用声学》2015,23(3):64-64
针对工业控制系统网络化和良好人机交互性的需求,构建和开发了基于ARM9微处理器的通用工业控制人机界面系统。硬件部分主要讨论了以S3C2440微处理器为核心的硬件电路设计,外围电路模块包括SDRAM及Flash存储器电路、以太网电路、RS-232/RS-422电路、触摸屏及LCD接口等电路,在分析了硬件系统信号完整性的前提下,完成了6层PCB的设计工作。软件部分主要研究了U-Boot移植和内核裁剪技术,编写了相关的硬件设备驱动程序,设计了基于QT/Embedded的人机界面和相关应用程序。论文研究最终实现了工业控制系统的人机交互和控制需求。  相似文献   
952.
In this paper, as a first step to study the global structure of solution, we treat a class of reaction–diffusion systems with competitive interaction, and discuss a uniqueness theorem of radially symmetric solutions for the system. To do this, the comparison principle and the shooting method are employed, and the spatial profile is investigated.  相似文献   
953.
We prove the existence of fast traveling pulse solutions in excitable media with non-local coupling. Existence results had been known, until now, in the case of local, diffusive coupling and in the case of a discrete medium, with finite-range, non-local coupling. Our approach replaces methods from geometric singular perturbation theory, that had been crucial in previous existence proofs, by a PDE oriented approach, relying on exponential weights, Fredholm theory, and commutator estimates.  相似文献   
954.
Let (W,S)(W,S) be a Coxeter system with a strictly complete Coxeter graph. The present paper concerns the set Red(z)Red(z) of all reduced expressions for any z∈WzW. By associating each bc-expression to a certain symbol, we describe the set Red(z)Red(z) and compute its cardinal |Red(z)||Red(z)| in terms of symbols. An explicit formula for |Red(z)||Red(z)| is deduced, where the Fibonacci numbers play a crucial role.  相似文献   
955.
考虑了带二元连续变利息力的Sparre Andersen风险模型.研究了积累值盈余过程的表达式与性质;在利率递增环境下,利用推广后的调节系数方程组与递归技术推导了最终破产概率的上界,结论表明得到的破产概率上界是更为一般的Lundberg指数上界.  相似文献   
956.
We consider the following system of fractional differential equations where is the Riemann‐Liouville fractional derivative of order α,f,g : [0,1] × [0, ∞ ) × [0, ∞ ) → [0, ∞ ). Sufficient conditions are provided for the existence of positive solutions to the considered problem. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
957.
958.
In this paper, sufficient conditions are established for the existence and uniqueness of global solutions to stochastic impulsive systems with expectations in the nonlinear terms. The maximal interval and the estimate of mild solutions are also discussed. These results are obtained by using the fixed point theorem, interval partition, and Lyapunov‐like technique. Finally, examples are given to illustrate the theory. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
959.
In this paper, we study an optimal control problem for the mixed boundary value problem for an elastic body with quasistatic evolution of an internal damage variable. We suppose that the evolution of microscopic cracks and cavities responsible for the damage is described by a nonlinear parabolic equation. A density of surface traction p acting on a part of boundary of an elastic body Ω is taken as a boundary control. Because the initial boundary value problem of this type can exhibit the Lavrentieff phenomenon and non‐uniqueness of weak solutions, we deal with the solvability of this problem in the class of weak variational solutions. Using the convergence concept in variable spaces and following the direct method in calculus of variations, we prove the existence of optimal and approximate solutions to the optimal control problem under rather general assumptions on the quasistatic evolution of damage. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
960.
In this paper, we consider the energy decay rate of a thermoelastic Bresse system with variable coefficients. Assume that the thermo-propagation in the system satisfies the Cattaneo's law, which can eliminate the paradox of infinite speed of thermal propagation in the assumption of the Fourier's law in the classical theory of thermoelasticity. Meanwhile, we also discuss the effect of a boundary viscoelastic damping on the stability of this system. By a detailed spectral analysis, we obtain the expressions of the spectrum and deduce some spectral properties of the system. Then based on the distribution of the spectrum, we prove that the energy of the system with a boundary viscoelastic damping decays exponentially. However, it no longer decays exponentially if there is no boundary damping. Copyright © 2013 John Wiley & Sons, Ltd.  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