全文获取类型
收费全文 | 11893篇 |
免费 | 1908篇 |
国内免费 | 779篇 |
专业分类
化学 | 3386篇 |
晶体学 | 56篇 |
力学 | 1878篇 |
综合类 | 234篇 |
数学 | 5131篇 |
物理学 | 3895篇 |
出版年
2024年 | 20篇 |
2023年 | 171篇 |
2022年 | 262篇 |
2021年 | 395篇 |
2020年 | 332篇 |
2019年 | 280篇 |
2018年 | 295篇 |
2017年 | 511篇 |
2016年 | 584篇 |
2015年 | 524篇 |
2014年 | 647篇 |
2013年 | 904篇 |
2012年 | 621篇 |
2011年 | 653篇 |
2010年 | 594篇 |
2009年 | 679篇 |
2008年 | 718篇 |
2007年 | 743篇 |
2006年 | 595篇 |
2005年 | 487篇 |
2004年 | 502篇 |
2003年 | 517篇 |
2002年 | 426篇 |
2001年 | 323篇 |
2000年 | 363篇 |
1999年 | 331篇 |
1998年 | 288篇 |
1997年 | 208篇 |
1996年 | 206篇 |
1995年 | 182篇 |
1994年 | 153篇 |
1993年 | 132篇 |
1992年 | 92篇 |
1991年 | 94篇 |
1990年 | 83篇 |
1989年 | 59篇 |
1988年 | 70篇 |
1987年 | 54篇 |
1986年 | 43篇 |
1985年 | 72篇 |
1984年 | 38篇 |
1983年 | 28篇 |
1982年 | 38篇 |
1981年 | 28篇 |
1980年 | 48篇 |
1979年 | 44篇 |
1978年 | 27篇 |
1977年 | 35篇 |
1976年 | 36篇 |
1957年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 718 毫秒
921.
We here provide two sided bounds for the density of the solution of a system of n differential equations of dimension d, the first one being forced by a non-degenerate random noise and the n−1 other ones being degenerate. The system formed by the n equations satisfies a suitable Hörmander condition: the second equation feels the noise plugged into the first equation, the third equation feels the noise transmitted from the first to the second equation and so on … , so that the noise propagates one way through the system. When the coefficients of the system are Lipschitz continuous, we show that the density of the solution satisfies Gaussian bounds with non-diffusive time scales. The proof relies on the interpretation of the density of the solution as the value function of some optimal stochastic control problem. 相似文献
922.
Wei Shyy Young-Chang Cho Amit Gupta Chien-Chou Tseng Ann Marie Sastry 《Acta Mechanica Sinica》2011,27(6):845-865
Successful modeling and/or design of engineering systems often requires one to address the impact of multiple "design variables" on the prescribed outcome.There are often multiple,competing objectives based on which we assess the outcome of optimization.Since accurate,high fidelity models are typically time consuming and computationally expensive,comprehensive evaluations can be conducted only if an efficient framework is available.Furthermore,informed decisions of the model/hardware’s overall performance rely on an adequate understanding of the global,not local,sensitivity of the individual design variables on the objectives.The surrogate-based approach,which involves approximating the objectives as continuous functions of design variables from limited data,offers a rational framework to reduce the number of important input variables,i.e.,the dimension of a design or modeling space.In this paper,we review the fundamental issues that arise in surrogate-based analysis and optimization,highlighting concepts,methods,techniques,as well as modeling implications for mechanics problems.To aid the discussions of the issues involved,we summarize recent efforts in investigating cryogenic cavitating flows,active flow control based on dielectric barrier discharge concepts,and lithium(Li)-ion batteries.It is also stressed that many multi-scale mechanics problems can naturally benefit from the surrogate approach for "scale bridging." 相似文献
923.
Chuan Fu College of Architecture North China University of Technology Beijing China 《Acta Mechanica Sinica》2011,27(5):817-822
The sealed,tuned liquid column gas damper (TLCGD) with gas-spring effect extends the frequency range of application and efficiently increases the modal structural damping.Active tuned liquid column gas damper (ATLCGD) is developed for the vibration control of plane asymmetric buildings subjected to earthquake excitation,improving the performance of the passive control scheme.The active behaviour is obtained by adjusting the pressure at the end of the liquid column using a pressurised reservoir.The classical linear quadratic regulator (LQR) design is presented as a straightforward approach to optimal control.Numerical simulations indicate a significant vibration reduction of plane asymmetric buildings by active control within the strong motion of the dynamic response. 相似文献
924.
925.
Maria Letizia Bertotti 《Applied mathematics and computation》2010,217(2):752-3793
In this paper a general framework is proposed, suitable for the modelling of the taxation and redistribution process in a closed society. This framework arises within a discrete kinetic approach for active particle systems, and is expressed by a system of nonlinear ordinary differential equations. It is intended to describe the evolution of the wealth distribution over the population, based on the interactions of single individuals. The framework is then employed towards the construction of a toy model, which is analytically and computationally investigated. 相似文献
926.
田玲玲 《数学的实践与认识》2010,40(15)
利用随机pooling设计的理论和方法,建立了数控机床可靠性筛选的定量分析数学模型,在统计分析观察工作时间段的基础上,可以筛选出可靠性差的数控机床,为数控机床的改进,产品质量的提高,提供理论依据. 相似文献
927.
Johannes Ledolter 《商业与工业应用随机模型》2010,26(4):473-480
We assume that the input in a transfer function noise model is determined by a proportional‐integral‐derivative controller that is subject to noise. We show how such a noisy feedback in the input series affects the standard Box–Jenkins method of specifying the transfer function model. Our findings have important implications for the analyst who uses the traditional Box–Jenkins approach. The analyst will be led to estimate an incorrect transfer function model if feedback (exact or noisy) is present. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
928.
A liquid sloshing absorber consists of a container, partially filled with liquid. The absorber is attached to the structure to be controlled, and relies on the structure’s motion to excite the liquid. Consequently, a sloshing wave is produced at the liquid free surface within the absorber, possessing energy dissipative qualities. The behaviour of liquid sloshing absorbers has been well documented, although their use in structural control applications has attracted considerably less attention. 相似文献
929.
In this paper, the value function for an optimal control problem with endpoint and state constraints is characterized as the unique lower semicontinuous generalized solution of the Hamilton-Jacobi equation. This is achieved under a constraint qualification (CQ) concerning the interaction of the state and dynamic constraints. The novelty of the results reported here is partly the nature of (CQ) and partly the proof techniques employed, which are based on new estimates of the distance of the set of state trajectories satisfying a state constraint from a given trajectory which violates the constraint. 相似文献
930.
本文利用专著(1) ̄(3)中的有关方法,讨论了一类具有滞后的中立型时变非线性控制系统的镇定与次优控制问题,得出了滞后量与非线性项的估计公式,并推广了文(4),(5)的结果。 相似文献