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   13716篇
  免费   2257篇
  国内免费   976篇
化学   4180篇
晶体学   57篇
力学   2870篇
综合类   426篇
数学   4350篇
物理学   5066篇
  2024年   39篇
  2023年   190篇
  2022年   367篇
  2021年   623篇
  2020年   498篇
  2019年   370篇
  2018年   358篇
  2017年   545篇
  2016年   653篇
  2015年   520篇
  2014年   729篇
  2013年   1130篇
  2012年   847篇
  2011年   790篇
  2010年   708篇
  2009年   779篇
  2008年   770篇
  2007年   791篇
  2006年   747篇
  2005年   621篇
  2004年   543篇
  2003年   574篇
  2002年   469篇
  2001年   407篇
  2000年   422篇
  1999年   357篇
  1998年   302篇
  1997年   276篇
  1996年   263篇
  1995年   188篇
  1994年   174篇
  1993年   156篇
  1992年   117篇
  1991年   96篇
  1990年   99篇
  1989年   54篇
  1988年   70篇
  1987年   44篇
  1986年   45篇
  1985年   44篇
  1984年   38篇
  1983年   10篇
  1982年   34篇
  1981年   21篇
  1980年   6篇
  1979年   7篇
  1978年   8篇
  1977年   12篇
  1959年   6篇
  1957年   13篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
991.
992.
In this paper, the pattern memory of the second-order neural networks with time-delay are investigated based on the stability theory. Several sufficient conditions are obtained such that the equilibrium point is locally exponential stable when the equilibrium point located in the saturation region. These conditions can be directly derived from the synaptic connection weights and the external input of the second-order neural networks, and be verified easily. In addition, four examples are given to show the effectiveness of the results.  相似文献   
993.
绘系统状态轨线的一种方法   总被引:4,自引:1,他引:3  
符五久 《大学物理》1999,18(2):21-23
介绍了一种作系统运动积分曲线的方法,并运用该方法绘出几个常见动力学系统的状态轨线,说明其实用价值。  相似文献   
994.
We present a model for scheduling power generation at a wind farm, and introduce a particle swarm optimization algorithm with a small world network structure to solve the model. The solution generated by the algorithm defines the operational status of wind turbines for a scheduling horizon selected by a decision maker. Different operational scenarios are constructed based on time series data of electricity price, grid demand, and wind speed. The computational results provide insights into management of a wind farm.  相似文献   
995.
Evaluation of fuzzy regression models by fuzzy neural network   总被引:1,自引:0,他引:1  
In this paper, a novel hybrid method based on fuzzy neural network for approximate fuzzy coefficients (parameters) of fuzzy linear and nonlinear regression models with fuzzy output and crisp inputs, is presented. Here a neural network is considered as a part of a large field called neural computing or soft computing. Moreover, in order to find the approximate parameters, a simple algorithm from the cost function of the fuzzy neural network is proposed. Finally, we illustrate our approach by some numerical examples.  相似文献   
996.
Even though existing algorithms for belief update in Bayesian networks (BNs) have exponential time and space complexity, belief update in many real-world BNs is feasible. However, in some cases the efficiency of belief update may be insufficient. In such cases minor improvements in efficiency may be important or even necessary to make a task tractable. This paper introduces two improvements to the message computation in Lazy propagation (LP): (1) we introduce myopic methods for sorting the operations involved in a variable elimination using arc-reversal and (2) extend LP with the any-space property. The performance impacts of the methods are assessed empirically.  相似文献   
997.
Directed transport of vortices in a Josephson junction network (JJN) with structural disorder is studied using a numerical simulation. Using spatiotemporal modulation of driving currents, the directed transport of vortices occurs even in the presence of disorder under certain conditions. From the analyses of the current–voltage and local voltage characteristics, it is found that the collective motion of vortices has an importance for the occurrence of directed transport.  相似文献   
998.
Mapping the conformational space of a polypeptide onto a network of conformational states involves a number of subjective choices, mostly in relation to the definition of conformation and its discrete nature in a network framework. Here, we evaluate the robustness of the topology of conformational‐space networks derived from Molecular Dynamics (MD) simulations with respect to the use of different discretization (clustering) methods, variation of their parameters, simulation length and analysis time‐step, and removing high‐frequency motions from the coordinate trajectories. In addition, we investigate the extent to which polypeptide dynamics can be reproduced on the resulting networks when assuming Markovian behavior. The analysis is based on eight 500 ns and eight 400 ns MD simulations in explicit water of two 10‐residue peptides. Three clustering algorithms were used, two of them based on the pair‐wise root‐mean‐square difference between structures and one on dihedral‐angle patterns. A short characteristic path length and a power‐law behavior of the probability distribution of the node degree are obtained irrespective of the clustering method or the value of any of the tested parameters. The average cliquishness is consistently one or two orders of magnitude larger than that of a random realization of a network of corresponding size and connectivity. The cliquishness as function of node degree and the kinetic properties of the networks are found to be most dependent on clustering method and/or parameters. Although Markovian simulations on the networks reproduce cluster populations accurately, their kinetic properties most often differ from those observed in the MD simulations. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010  相似文献   
999.
1000.
Provided that 13C‐detected NMR experiments are either preferable or complementary to 1H detection, we report here tools to determine Cα? C′, C′? N, and Cα? Hα residual dipolar couplings on the basis of the CON experiment. The coupling constants determined on ubiquitin are consistent with the subset measured with the 1H‐detected HNCO sequences. Since the utilization of residual dipolar couplings may depend on the mobility of the involved nuclei, we also provide tools to measure longitudinal and transverse relaxation rates of N and C′. This new set of experiments is a further development of a whole strategy based on 13C direct‐detection NMR spectroscopy for the study of biological macromolecules.  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