全文获取类型
收费全文 | 10765篇 |
免费 | 1683篇 |
国内免费 | 482篇 |
专业分类
化学 | 1924篇 |
晶体学 | 44篇 |
力学 | 1721篇 |
综合类 | 208篇 |
数学 | 5658篇 |
物理学 | 3375篇 |
出版年
2024年 | 16篇 |
2023年 | 145篇 |
2022年 | 259篇 |
2021年 | 307篇 |
2020年 | 259篇 |
2019年 | 244篇 |
2018年 | 244篇 |
2017年 | 462篇 |
2016年 | 530篇 |
2015年 | 469篇 |
2014年 | 591篇 |
2013年 | 806篇 |
2012年 | 573篇 |
2011年 | 582篇 |
2010年 | 526篇 |
2009年 | 646篇 |
2008年 | 680篇 |
2007年 | 685篇 |
2006年 | 532篇 |
2005年 | 424篇 |
2004年 | 427篇 |
2003年 | 437篇 |
2002年 | 379篇 |
2001年 | 276篇 |
2000年 | 290篇 |
1999年 | 278篇 |
1998年 | 245篇 |
1997年 | 190篇 |
1996年 | 182篇 |
1995年 | 161篇 |
1994年 | 123篇 |
1993年 | 99篇 |
1992年 | 76篇 |
1991年 | 81篇 |
1990年 | 68篇 |
1989年 | 55篇 |
1988年 | 59篇 |
1987年 | 49篇 |
1986年 | 40篇 |
1985年 | 68篇 |
1984年 | 36篇 |
1983年 | 28篇 |
1982年 | 36篇 |
1981年 | 30篇 |
1980年 | 47篇 |
1979年 | 46篇 |
1978年 | 27篇 |
1977年 | 37篇 |
1976年 | 38篇 |
1974年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
851.
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
852.
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
853.
854.
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
855.
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
856.
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
857.
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
858.
M. R. Caputo 《Journal of Optimization Theory and Applications》1999,101(3):723-730
Theorem 2.1 of Caputo (Ref. 1) linking the optimal solution functions and optimal value functions of reciprocal pairs of isoperimetric control problems is correct, but requires stronger assumptions than those used explicitly to establish its veracity. One such set of stronger assumptions is provided in this note. 相似文献
859.
Comparisons are made between the expected gain of a prophet (an observer with complete foresight) and the maximal expected gain of a gambler (using only non-anticipating stopping times) observing a sequence of independent, uniformly bounded random variables where a non-negative fixed cost is charged for each observation. Sharp universal bounds are obtained under various restrictions on the cost and the length of the sequence. For example, it is shown for X1, X2, … independent, [0, 1]-valued random variables that for all c ≥ 0 and all n ≥ 1 that E(max1 ≤ j ≤ n(Xj − jc)) − supt Tn E(Xt − tc) ≤ 1/e, where Tn is the collection of all stopping times t which are less than or equal to n almost surely. 相似文献
860.
We study deterministic discounted optimal control problems associated with discrete-time systems. It is shown that, for small discount rates, the controllability properties of the underlying system can guarantee the convergence of the discounted value function to the value function of the average yield. An application in the theory of exponential growth rates of discrete inclusions is presented. This application motivates the analysis of infinite-horizon optimal control problems with running yields that are unbounded from below. 相似文献