全文获取类型
收费全文 | 14538篇 |
免费 | 957篇 |
国内免费 | 821篇 |
专业分类
化学 | 217篇 |
晶体学 | 2篇 |
力学 | 1449篇 |
综合类 | 167篇 |
数学 | 13354篇 |
物理学 | 1127篇 |
出版年
2024年 | 30篇 |
2023年 | 140篇 |
2022年 | 181篇 |
2021年 | 203篇 |
2020年 | 323篇 |
2019年 | 332篇 |
2018年 | 381篇 |
2017年 | 388篇 |
2016年 | 373篇 |
2015年 | 277篇 |
2014年 | 612篇 |
2013年 | 1150篇 |
2012年 | 653篇 |
2011年 | 766篇 |
2010年 | 683篇 |
2009年 | 942篇 |
2008年 | 994篇 |
2007年 | 1022篇 |
2006年 | 901篇 |
2005年 | 698篇 |
2004年 | 603篇 |
2003年 | 668篇 |
2002年 | 577篇 |
2001年 | 432篇 |
2000年 | 445篇 |
1999年 | 394篇 |
1998年 | 366篇 |
1997年 | 327篇 |
1996年 | 248篇 |
1995年 | 205篇 |
1994年 | 139篇 |
1993年 | 122篇 |
1992年 | 119篇 |
1991年 | 104篇 |
1990年 | 79篇 |
1989年 | 40篇 |
1988年 | 41篇 |
1987年 | 39篇 |
1986年 | 41篇 |
1985年 | 54篇 |
1984年 | 53篇 |
1983年 | 29篇 |
1982年 | 28篇 |
1981年 | 25篇 |
1980年 | 18篇 |
1979年 | 22篇 |
1978年 | 14篇 |
1977年 | 15篇 |
1976年 | 9篇 |
1936年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
When we consider an error model in a quantum computing system, we assume a parametric model where a prepared qubit belongs. Keeping this in mind, we focus on the evaluation of the amount of information we obtain when we know the system belongs to the model within the parameter range. Excluding classical fluctuations, uncertainty still remains in the system. We propose an information quantity called purely quantum information to evaluate this and give it an operational meaning. For the qubit case, it is relevant to the facility location problem on the unit sphere, which is well known in operations research. For general cases, we extend this to the facility location problem in complex projective spaces. Purely quantum information reflects the uncertainty of a quantum system and is related to the minimum entropy rather than the von Neumann entropy. 相似文献
32.
We study 2×2 systems of hyperbolic conservation laws near an umbilic point. These systems have Undercompressive shock wave solutions, i.e., solutions whose viscous profiles are represented by saddle connections in an associated family of planar vector fields. Previous studies near umbilic points have assumed that the flux function is a quadratic polynomial, in which case saddle connections lie on invariant lines. We drop this assumption and study saddle connections using Golubitsky-Schaeffer equilibrium bifurcation theory and the Melnikov integral, which detects the breaking of heteroclinic orbits. The resulting information is used to construct solutions of Riemann problems. 相似文献
33.
A. M. Khludnev 《Journal of Applied Mechanics and Technical Physics》2008,49(4):553-567
The contact problem for two elastic plates aligned at a prescribed angle to each other is considered. The set of contact points
is assumed to be unknown in advance and to be determined only after the problem is solved. Various formulations of the problem
are given, and their equivalence is proved. A complete set of boundary conditions fulfilled on the contact domain is found,
and the character of satisfaction of these conditions is described. The asymptotic properties of solutions are studied for
rigidity parameters of the contacting plates tending to infinity.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 4, pp. 42–58, July–August, 2008. 相似文献
34.
This paper investigates the exact and approximate spectrum assignment properties associated with realizable output-feedback pole-placement type controllers for single-input single-output linear time-invariant time-delay systems with commensurate point delays. The controller synthesis problem is discussed through the solvability of a set of coupled diophantine equations of polynomials. An extra complexity is incorporated to the above design to cancel extra unsuitable dynamics being generated when solving the above diophantine equations. Thus, the complete controller tracks any arbitrary prefixed (either finite or delaydependent) closed-loop spectrum. However, if the controller is simplified by deleting the above mentioned extra complexity, then the robust stability and approximated spectrum assignment are still achievable for a certain sufficiently small amount of delayed dynamics. Finally, the approximate spectrum assignment and robust stability problems are revisited under plant disturbances if the nominal controller is maintained. In the current approach, the finite spectrum assignment is only considered as a particular case to the designer‘s choice of a (delay-dependent) arbitrary spectrum assignment objective. 相似文献
35.
透平叶栅三维粘性气动反问题的控制理论方法 总被引:2,自引:0,他引:2
将基于控制理论的形状优化设计方法应用于粘性可压流动条件下的透平叶栅三维气动反设计,详细推导了三维N-S方程伴随系统的偏微分方程组及其各类边界条件.讨论了伴随系统的解的适定性条件,并由此给出应用N-S方程进行气动优化的目标函数的选取限制.研究了伴随方程的数值求解技术,给出敏感性导数的最终计算式,结合拟牛顿算法发展了三维透平叶栅粘性反问题的气动设计方法. 相似文献
36.
37.
38.
A field of endomorphisms R is called a Nijenhuis operator if its Nijenhuis torsion vanishes. In this work we study a specific kind of singular points of R called points of scalar type. We show that the tangent space at such points possesses a natural structure of a left-symmetric algebra (also known as pre-Lie or Vinberg-Kozul algebras). Following Weinstein's approach to linearization of Poisson structures, we state the linearisation problem for Nijenhuis operators and give an answer in terms of non-degenerate left-symmetric algebras. In particular, in dimension 2, we give classification of non-degenerate left-symmetric algebras for the smooth category and, with some small gaps, for the analytic one. These two cases, analytic and smooth, differ. We also obtain a complete classification of two-dimensional real left-symmetric algebras, which may be an interesting result on its own. 相似文献
39.
In this paper, we generalize the well-known Lyapunov-type inequality for second-order linear differential equations to a class of even-order linear differential equations, the results of this paper are new and generalize some known inequalities in the literatures. 相似文献
40.
Coleman自同构群的投射极限 总被引:2,自引:0,他引:2
在这篇注记中,利用群的投射极限性质给出了有限可解群的Coleman自同构群的一个具体构造.作为应用,证明了二面体群的Coleman外自同构群或者是1或者是一个初等阿贝尔2-群. 相似文献