全文获取类型
收费全文 | 3034篇 |
免费 | 761篇 |
国内免费 | 113篇 |
专业分类
化学 | 373篇 |
晶体学 | 9篇 |
力学 | 736篇 |
综合类 | 70篇 |
数学 | 754篇 |
物理学 | 1966篇 |
出版年
2024年 | 2篇 |
2023年 | 25篇 |
2022年 | 78篇 |
2021年 | 98篇 |
2020年 | 95篇 |
2019年 | 61篇 |
2018年 | 64篇 |
2017年 | 154篇 |
2016年 | 176篇 |
2015年 | 128篇 |
2014年 | 198篇 |
2013年 | 191篇 |
2012年 | 221篇 |
2011年 | 210篇 |
2010年 | 166篇 |
2009年 | 175篇 |
2008年 | 213篇 |
2007年 | 189篇 |
2006年 | 141篇 |
2005年 | 161篇 |
2004年 | 151篇 |
2003年 | 127篇 |
2002年 | 136篇 |
2001年 | 124篇 |
2000年 | 104篇 |
1999年 | 86篇 |
1998年 | 73篇 |
1997年 | 81篇 |
1996年 | 57篇 |
1995年 | 48篇 |
1994年 | 36篇 |
1993年 | 25篇 |
1992年 | 24篇 |
1991年 | 16篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1987年 | 13篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1974年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有3908条查询结果,搜索用时 109 毫秒
131.
132.
In this paper, we propose an adaptive defect-correction method for natural convection (NC) equations. A defect-correction method (DCM) is proposed for solving NC equations to overcome the convection dominance problem caused by a high Rayleigh number. To solve the large amount of computation and the discontinuity of the gradient of the numerical solution, we combine a new recovery-type posteriori estimator in view of the gradient recovery and superconvergent theory. The presented reliability and efficiency analysis shows that the true error can be effectively bounded by the recovery-based error estimator. Finally, the stability, accuracy and efficiency of the proposed method are confirmed by several numerical investigations. 相似文献
133.
This study focuses on the full-form model-free adaptive controller (FFMFAC) for SISO discrete-time nonlinear systems, and proposes enhanced FFMFAC. The proposed technique design incorporates long short-term memory neural networks (LSTMs) and fuzzy neural networks (FNNs). To be more precise, LSTMs are utilized to adjust vital parameters of the FFMFAC online. Additionally, due to the high nonlinear approximation capabilities of FNNs, pseudo gradient (PG) values of the controller are estimated online. EFFMFAC is characterized by utilizing the measured I/O data for the online training of all introduced neural networks and does not involve offline training and specific models of the controlled system. Finally, the rationality and superiority are verified by two simulations and a supporting ablation analysis. Five individual performance indices are given, and the experimental findings show that EFFMFAC outperforms all other methods. Especially compared with the FFMFAC, EFFMFAC reduces the by 21.69% and 11.21%, respectively, proving it to be applicable for SISO discrete-time nonlinear systems. 相似文献
134.
本研究从业主—承包商交互的视角构建了一种RCPSP(resource-constrained project scheduling problem)双层优化模型,即在可更新资源约束条件下,项目双方如何进行交互决策达到双方NPV(Net present value)最大化的目标。首先对研究问题进行界定,构建资源约束下的max-NPV项目调度双层优化模型;然后利用延迟优先规则设计了一种基于时间窗延迟的嵌套式自适应遗传算法来求解该模型,以达到双方NPV最大化;最后用一个算例验证算法的有效性,同时通过PSPLIB数值实验说明算法的稳定性,并分析关键参数对项目双方收益的影响。研究结果为项目进程的安排以及奖励机制的设计提供依据,以提高双方利益。 相似文献
135.
求一类多元多峰函数全局极小的区间斜率方法 总被引:7,自引:0,他引:7
Based on the interval analysis, an interval slope method is proposed for finding all global minimizers of a several peaks function f on domain X^0包含于R^n, which is given by interval slope discard tests and interval extension of objective function.Numerical results of representative test functions show that this method is practical and effective. 相似文献
136.
基于进化博弈视角的水源地与下游生态补偿合作演化分析 总被引:1,自引:0,他引:1
水源地与下游地方政府之间的协议合作可以协调流域上下游之间的矛盾和利益,是一种可实现流域生态保护良性循环的生态补偿尝试。本文应用进化博弈的双种群博弈理论,研究了水源地和下游地方政府之间博弈演化过程及影响因素。研究表明,流域上下游地方政府合作的演化方向主要受水源地不保护及下游不补偿受到的惩罚、下游对水源地的补偿额度、水源地和下游合作的初始成本、水源地生态保护的成本及收益等八个因素的影响。降低水源地的保护成本及水源地和下游合作的初始成本,提高水源地因保护而获得的综合效益、提高水源地不保护及下游不补偿受到的惩罚额度、合理确定下游对水源地的补偿额度将有利于水源地生态补偿机制向合作方向演进。 相似文献
137.
Recent anthropological studies have demonstrated that low latitude ‘encounter’ foragers exploit their environments in energetically very efficient manners and closely track the environment as it changes. The paper begins to investigate how they manage to do this by proposing a simple decision making and learning rule developed from an evolutionary ecological basis. Having described the mathematical model the paper refers to simulation studies exploring this model which suggest that some of the seemingly complex aspects of hunter gatherer behaviour may result from the use of simple decision making and learning processes. 相似文献
138.
It is proposed that continuous time is in effect discretized in the brain by dynamic pattern recognition mechanisms in neurons. Time discretization is required to support formal computations in continuous time systems consisting of a large number of components. The ability to perform formal computations is necessary if the system is to execute high level algorithms of the type used in present day artificial intelligence. The weakness of such algorithms is that they work efficiently only when the forms of patterns and objects presented to them are highly constrained. The dynamic mechanisms which discretize the brain's time line also serve to code patterns into constrained forms suitable for high level processing. 相似文献
139.
In this paper it is shown, by means of simulation, that interesting time behavior is observed for damaged and overloaded networks, and that adaptive, decentralized intelligence can have a dramatic influence on the overall network performance. The time behavior of nonhierarchical networks is modeled by a system of nonlinear difference equations among global variables, and bistability is shown to exist. Using a simple adaptive control mechanism, it is shown that, depending upon the value of a certain network variable, either limit cycle or steady state behavior results. A few ideas are discussed for applications of nonhierarchical communications to cellular automata and to decision-making systems. 相似文献
140.
针对不确定非线性生物系统—W illis环状脑动脉瘤系统,利用高斯型模糊逻辑系统的逼近能力及新构造的Lyapunov函数,基于模糊建模提出了一种自适应模糊控制器设计的新方案.该方案把逼近误差引入到控制器设计条件中用以改善系统的动态性能.不但设计简单还保证了控制方法的鲁棒性与稳定性.通过反向传播算法调整模糊基函数参数及递归最小二乘法调整参数向量,θ更新控制律,实现了理想跟踪.从理论上研究了脑动脉瘤内血流速度的非线性行为及控制,具有实际意义.仿真结果表明该控制方法的有效性. 相似文献