全文获取类型
收费全文 | 101828篇 |
免费 | 1676篇 |
国内免费 | 1161篇 |
专业分类
化学 | 34909篇 |
晶体学 | 1235篇 |
力学 | 8192篇 |
综合类 | 44篇 |
数学 | 34042篇 |
物理学 | 26243篇 |
出版年
2023年 | 211篇 |
2022年 | 390篇 |
2021年 | 370篇 |
2020年 | 355篇 |
2019年 | 327篇 |
2018年 | 10779篇 |
2017年 | 10553篇 |
2016年 | 6621篇 |
2015年 | 1328篇 |
2014年 | 1003篇 |
2013年 | 1577篇 |
2012年 | 5172篇 |
2011年 | 12188篇 |
2010年 | 6842篇 |
2009年 | 7286篇 |
2008年 | 7939篇 |
2007年 | 10011篇 |
2006年 | 1543篇 |
2005年 | 2401篇 |
2004年 | 2484篇 |
2003年 | 2708篇 |
2002年 | 1744篇 |
2001年 | 1356篇 |
2000年 | 1088篇 |
1999年 | 897篇 |
1998年 | 709篇 |
1997年 | 659篇 |
1996年 | 646篇 |
1995年 | 485篇 |
1994年 | 436篇 |
1993年 | 402篇 |
1992年 | 372篇 |
1991年 | 328篇 |
1990年 | 292篇 |
1989年 | 278篇 |
1988年 | 232篇 |
1987年 | 216篇 |
1986年 | 186篇 |
1985年 | 201篇 |
1984年 | 152篇 |
1983年 | 130篇 |
1982年 | 105篇 |
1981年 | 114篇 |
1980年 | 96篇 |
1979年 | 79篇 |
1978年 | 73篇 |
1977年 | 66篇 |
1976年 | 75篇 |
1975年 | 61篇 |
1973年 | 58篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
Zhi CHENG Yu YE 《数学学报(英文版)》2007,23(6):965-972
We introduce the category of t-fold modules which is a full subcategory of graded modules over a graded algebra. We show that this subcategory and hence the subcategory of t-Koszul modules are both closed under extensions and cokernels of monomorphisms. We study the one-point extension algebras, and a necessary and sufficient condition for such an algebra to be t-Koszul is given. We also consider the conditions such that the category of t-Koszul modules and the category of quadratic modules coincide. 相似文献
942.
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
943.
Let L be an elliptic operator, we give arguments about the duality estimate between Morrey spaces and its pre-dual spaces characterized by the heat kernel associated to L that is given in [6],[8]. 相似文献
944.
Thi Thu Van Nguyen Jean-Jacques Strodiot Van Hien Nguyen 《Journal of Global Optimization》2009,44(2):175-192
In this article we present a new and efficient method for solving equilibrium problems on polyhedra. The method is based on
an interior-quadratic proximal term which replaces the usual quadratic proximal term. This leads to an interior proximal type
algorithm. Each iteration consists in a prediction step followed by a correction step as in the extragradient method. In a
first algorithm each of these steps is obtained by solving an unconstrained minimization problem, while in a second algorithm
the correction step is replaced by an Armijo-backtracking linesearch followed by an hyperplane projection step. We prove that
our algorithms are convergent under mild assumptions: pseudomonotonicity for the two algorithms and a Lipschitz property for
the first one. Finally we present some numerical experiments to illustrate the behavior of the proposed algorithms. 相似文献
945.
Yan-nan LIU & Huai-yu JIAN Department of Mathematical Sciences Tsinghua University Beijing China 《中国科学A辑(英文版)》2007,50(2):231-239
In this paper, we study the evolution of hypersurface moving by the mean curvature minus an external force field. It is shown that the flow will blow up in a finite time if the mean curvature of the initial surface is larger than some constant depending on the boundness of derivatives of the external force field. For a linear force, we prove that the convexity of the hypersurface is preserved during the evolution and the flow has a unique smooth solution in any finite time and expands to infinity as the time tends to infinity if the initial curvature is smaller than the slope of the force. 相似文献
946.
A highly nonnormal Jacobian may give rise to large transients. This behaviour has been shown to have implications for (a) the relevance of linearising a nonlinear system and (b) the timestep restrictions required to keep a numerical method stable. Here, we show that nonnormality also manifests itself for stochastic differential equations. We give an example of a family of systems that is stable without noise, but can be made exponentially unstable in mean-square by a noise perturbation that shrinks to zero as the nonnormality increases. We then show via finite-time convergence theory that an Euler approximation shares the same property, giving a discrete analogue of the result. In memory of Germund Dahlquist (1925–2005).AMS subject classification (2000) 65C30, 34F05 相似文献
947.
Towards a unified recurrent neural network theory: The uniformly pseudo-projection-anti-monotone net
In the past decades, various neural network models have been developed for modeling the behavior of human brain or performing
problem-solving through simulating the behavior of human brain. The recurrent neural networks are the type of neural networks
to model or simulate associative memory behavior of human being. A recurrent neural network (RNN) can be generally formalized
as a dynamic system associated with two fundamental operators: one is the nonlinear activation operator deduced from the input-output
properties of the involved neurons, and the other is the synaptic connections (a matrix) among the neurons. Through carefully
examining properties of various activation functions used, we introduce a novel type of monotone operators, the uniformly
pseudo-projectionanti-monotone (UPPAM) operators, to unify the various RNN models appeared in the literature. We develop a
unified encoding and stability theory for the UPPAM network model when the time is discrete. The established model and theory
not only unify but also jointly generalize the most known results of RNNs. The approach has lunched a visible step towards
establishment of a unified mathematical theory of recurrent neural networks. 相似文献
948.
可调谐二极管激光吸收光谱法测量气体温度 总被引:3,自引:1,他引:2
研究了一种新型的非接触式测温技术——可调谐二极管激光吸收光谱(TDLAS)测温技术。介绍了温度测量及调制吸收光谱技术原理,分析了调制幅度对气体温度测量的影响。优选了氧气吸收谱线对13163.78 cm-1和13164.18 cm-1,在搭建的高温实验系统上,实现了气体温度和浓度的同时测量。通过分析实测波形获得了谱线13164.18 cm-1在823~1323 K温度范围内的碰撞展宽系数和温度指数。实验结果表明,在823~1323 K温度范围内,系统温度测量的线性误差为0.65%,最大波动为±15 K。 相似文献
949.
Zhao Qiaoling Yan Guojun 《高校应用数学学报(英文版)》2007,22(3):343-352
In this paper,the stochastic flow of mappings generated by a Feller convolution semigroup on a compact metric space is studied.This kind of flow is the generalization of superprocesses of stochastic flows and stochastic diffeomorphism induced by the strong solutions of stochastic differential equations. 相似文献
950.
The computational problems of two special determinants are investigated. Those tion for computing Fredholm integral equation of the second kind. The main tool to be used in this paper is the well-known Schur complement theorem. 相似文献