全文获取类型
收费全文 | 17665篇 |
免费 | 1744篇 |
国内免费 | 715篇 |
专业分类
化学 | 4752篇 |
晶体学 | 17篇 |
力学 | 1324篇 |
综合类 | 141篇 |
数学 | 9016篇 |
物理学 | 4874篇 |
出版年
2024年 | 23篇 |
2023年 | 179篇 |
2022年 | 212篇 |
2021年 | 380篇 |
2020年 | 439篇 |
2019年 | 461篇 |
2018年 | 347篇 |
2017年 | 396篇 |
2016年 | 621篇 |
2015年 | 495篇 |
2014年 | 793篇 |
2013年 | 1330篇 |
2012年 | 764篇 |
2011年 | 824篇 |
2010年 | 772篇 |
2009年 | 1019篇 |
2008年 | 1207篇 |
2007年 | 1249篇 |
2006年 | 1033篇 |
2005年 | 769篇 |
2004年 | 659篇 |
2003年 | 739篇 |
2002年 | 716篇 |
2001年 | 545篇 |
2000年 | 567篇 |
1999年 | 494篇 |
1998年 | 460篇 |
1997年 | 361篇 |
1996年 | 278篇 |
1995年 | 219篇 |
1994年 | 210篇 |
1993年 | 193篇 |
1992年 | 175篇 |
1991年 | 127篇 |
1990年 | 106篇 |
1989年 | 102篇 |
1988年 | 114篇 |
1987年 | 88篇 |
1986年 | 79篇 |
1985年 | 112篇 |
1984年 | 88篇 |
1983年 | 29篇 |
1982年 | 56篇 |
1981年 | 50篇 |
1980年 | 51篇 |
1979年 | 44篇 |
1978年 | 39篇 |
1977年 | 37篇 |
1976年 | 36篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
A. V. Kravtsov 《Computational Mathematics and Mathematical Physics》2007,47(11):1875-1884
A linear problem of parametric oscillations of a low-viscous two-layer fluid in a closed vessel partially filled with a porous medium is studied. An asymptotic solution is constructed on the basis of combined application of boundary functions and averaging methods. Approximate formulas for boundaries of instability domains in the case of subharmonic and harmonic resonances are derived. 相似文献
162.
We construct separation variables for the Kovalevskaya–Goryachev–Chaplygin gyrostat for arbitrary values of the parameters. We show that different separation variables can be constructed for the same integrable system if different integrals of motion are chosen. 相似文献
163.
Marta Gimnez-Pedrs Ali Aghmiz Carmen Claver Anna M. Masdeu-Bult Denis Sinou 《Journal of molecular catalysis. A, Chemical》2003,200(1-2):157-163
High linear alkenes (1-octene and 1-decene) have been hydroformylated using water-soluble rhodium complexes associated with sulfonated diphosphines in the presence of ionic surfactants or methanol. In all cases, the hydroformylation activities were higher than in experiments without additives. The selectivity in aldehydes was higher when we used cetyltrimethylammonium hydrogensulfate (CTAHSO4) as the surfactant or methanol as the co-solvent. 相似文献
164.
In a seminal paper, Martin Clark (Communications Systems and Random Process Theory, Darlington, 1977, pp. 721–734, 1978) showed how the filtered dynamics giving the optimal estimate of a Markov chain observed in Gaussian noise can be expressed
using an ordinary differential equation. These results offer substantial benefits in filtering and in control, often simplifying
the analysis and an in some settings providing numerical benefits, see, for example Malcolm et al. (J. Appl. Math. Stoch.
Anal., 2007, to appear).
Clark’s method uses a gauge transformation and, in effect, solves the Wonham-Zakai equation using variation of constants.
In this article, we consider the optimal control of a partially observed Markov chain. This problem is discussed in Elliott
et al. (Hidden Markov Models Estimation and Control, Applications of Mathematics Series, vol. 29, 1995). The innovation in our results is that the robust dynamics of Clark are used to compute forward in time dynamics for a simplified
adjoint process. A stochastic minimum principle is established. 相似文献
165.
Wing-Sum Cheung Patricia J.Y. Wong 《Journal of Mathematical Analysis and Applications》2007,329(2):851-869
We consider a system of focal boundary value problems where the nonlinearities may be singular in the independent variable and may also be singular in the dependent arguments. Using Schauder fixed point theorem, we establish criteria such that the system of boundary value problems has at least one fixed-sign solution. 相似文献
166.
《中国科学A辑(英文版)》2007,(7)
The double loop network(DLN)is a circulant digraph with n nodes and outdegree 2.It is an important topological structure of computer interconnection networks and has been widely used in the designing of local area networks and distributed systems.Given the number n of nodes,how to construct a DLN which has minimum diameter?This problem has attracted great attention.A related and longtime unsolved problem is:for any given non-negative integer k,is there an infinite family of k-tight optimal DLN?In this paper,two main results are obtained:(1)for any k≥0,the infinite families of k-tight optimal DLN can be constructed,where the number n(k,e,c)of their nodes is a polynomial of degree 2 in e with integral coefficients containing a parameter c.(2)for any k≥0, an infinite family of singular k-tight optimal DLN can be constructed. 相似文献
167.
Marco Merkli 《Journal of Mathematical Analysis and Applications》2007,327(1):376-399
Level shift operators describe the second-order displacement of eigenvalues under perturbation. They play a central role in resonance theory and ergodic theory of open quantum systems at positive temperatures. We exhibit intrinsic properties of level shift operators, properties which stem from the structure of open quantum systems at positive temperatures and which are common to all such systems. They determine the geometry of resonances bifurcating from eigenvalues of positive temperature Hamiltonians and they relate the Gibbs state, the kernel of level shift operators, and zero energy resonances. We show that degeneracy of energy levels of the small part of the open quantum system causes the Fermi Golden Rule Condition to be violated and we analyze ergodic properties of such systems. 相似文献
168.
电力市场中合同电量与竞争电量交易比例的研究 总被引:1,自引:0,他引:1
在单边开放的区域电力市场中,合理的合同电量与竞争电量交易比例是保证电力市场有效运行的一个重要环节。竞争电量所占的比例将主要取决于当前发电公司的市场行为。首先使用BP神经网络对电力需求弹性系数进行了预测,然后以长期电力市场均衡为目标函数,考虑贵州电网发电机组的可用容量与负荷预测的误差,以及贵州输电线路的可靠性诸因素,推导出合同电量与竞争电量交易比例,经过与南方区域电力市场目前运营规则规定的交易比例比较,该比例是合理的,可以规避电力市场价格波动等带来的风险。 相似文献
169.
In this paper a class of impulsive differential inclusions is investigated. The existence of solution bundle is proved. And we also construct a nonlinear semigroup of operators on cb(E) (closed-bounded subset of E) to describe the set of attainable states. 相似文献
170.
We study the properties of multifunction operators that are contractive in the Covitz-Nadler sense. In this situation, such operators T possess fixed points satisfying the relation x∈Tx. We introduce an iterative method involving projections that guarantees convergence from any starting point x0∈X to a point x∈XT, the set of all fixed points of a multifunction operator T. We also prove a continuity result for fixed point sets XT as well as a “generalized collage theorem” for contractive multifunctions. These results can then be used to solve inverse problems involving contractive multifunctions. Two applications of contractive multifunctions are introduced: (i) integral inclusions and (ii) iterated multifunction systems. 相似文献