全文获取类型
收费全文 | 471861篇 |
免费 | 4055篇 |
国内免费 | 1366篇 |
专业分类
化学 | 210670篇 |
晶体学 | 6820篇 |
力学 | 26571篇 |
综合类 | 7篇 |
数学 | 86931篇 |
物理学 | 146283篇 |
出版年
2021年 | 3360篇 |
2020年 | 3512篇 |
2019年 | 3964篇 |
2018年 | 19878篇 |
2017年 | 20280篇 |
2016年 | 15367篇 |
2015年 | 5737篇 |
2014年 | 7677篇 |
2013年 | 16785篇 |
2012年 | 18886篇 |
2011年 | 32598篇 |
2010年 | 21212篇 |
2009年 | 21543篇 |
2008年 | 26932篇 |
2007年 | 31086篇 |
2006年 | 12994篇 |
2005年 | 17225篇 |
2004年 | 14027篇 |
2003年 | 13218篇 |
2002年 | 10941篇 |
2001年 | 10816篇 |
2000年 | 8255篇 |
1999年 | 6194篇 |
1998年 | 5245篇 |
1997年 | 5039篇 |
1996年 | 4880篇 |
1995年 | 4126篇 |
1994年 | 4057篇 |
1993年 | 3914篇 |
1992年 | 4263篇 |
1991年 | 4480篇 |
1990年 | 4270篇 |
1989年 | 4181篇 |
1988年 | 3955篇 |
1987年 | 4088篇 |
1986年 | 3837篇 |
1985年 | 4801篇 |
1984年 | 4869篇 |
1983年 | 4053篇 |
1982年 | 4137篇 |
1981年 | 3842篇 |
1980年 | 3812篇 |
1979年 | 4078篇 |
1978年 | 4074篇 |
1977年 | 3979篇 |
1976年 | 3968篇 |
1975年 | 3714篇 |
1974年 | 3662篇 |
1973年 | 3724篇 |
1972年 | 2642篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
991.
On a Definitizable Analog of the Trigonometric Moment Problem Generating an Indefinite Toeplitz Form
We prove the existence of an integro-polynomial representation for a sequence of numbers such that there exists a difference operator mapping this sequence to a sequence that generates the solvable trigonometric moment problem. A similar result related to the power moment problem was given in [12]. 相似文献
992.
A carousel is a dynamical system that describes the movement of an equilateral linkage in which the midpoint of each rod travels parallel to it. They are closely related to the floating body problem. We prove, using the work of Auerbach, that any figure that floats in equilibrium in every position is drawn by a carousel. Of special interest are such figures with rational perimetral density of the floating chords, which are then drawn by carousels. In particular, we prove that for some perimetral densities the only such figure is the circle, as the problem suggests. 相似文献
993.
Shea-Ming Oon 《Periodica Mathematica Hungarica》2004,49(2):107-118
In this paper we study some pseudo-random properties related to the prime factors of integers. We prove some results concerning the well distribution of the greatest prime factor modulo 4, and give some computational insight on the correlations, which seem to be beyond reach of proof. 相似文献
994.
Clemens Heuberger 《Periodica Mathematica Hungarica》2004,49(2):65-89
We study digit expansions with arbitrary integer digits in base q (q integer) and the Fibonacci base such that the sum of the absolute values of the digits is minimal. For the Fibonacci case, we describe a unique minimal expansion and give a greedy algorithm to compute it. Additionally, transducers to calculate minimal expansions from other expansions are given. For the case of even integer bases q, similar results are given which complement those given in [6]. 相似文献
995.
A note on a generalized Douglas space 总被引:1,自引:0,他引:1
Periodica Mathematica Hungarica - 相似文献
996.
Beatriz S. D'Ambrosio William J. Boone Shelly Sheats Harkness 《School science and mathematics》2004,104(1):5-15
This paper describes the mechanism used to gain insights into the state of the art of mathematics instruction in a large urban district in order to design meaningful professional development for the teachers in the district. Surveys of close to 2,000 elementary, middle school, and high school students were collected in order to assess the instructional practices used in mathematics classes across the district. Students were questioned about the frequency of use of various instructional practices that support the meaningful learning of mathematics. These included practices such as problem solving, use of calculators and computers, group work, homework, discussions, and projects, among others. Responses were analyzed and comparisons were drawn between elementary and middle school students' responses and between middle school and high school responses. Finally, fifth‐grade student responses were compared to those of their teachers. Student responses indicated that they had fewer inquiry‐based experiences, fewer student‐to‐student interactions, and fewer opportunities to defend their answers and justify their thinking as they moved from elementary to middle school to high school. In the elementary grades students reported an overemphasis on the use of memorization of facts and procedures and sparse use of calculators. Results were interpreted and specific directions for professional development, as reported in this paper, were drawn from these data. The paper illustrates how student surveys can inform the design of professional development experiences for the teachers in a district. 相似文献
997.
998.
Karin Cvetko-Vah 《Semigroup Forum》2004,68(2):268-279
Given a ring $R$, let $S\subseteq R$ be a pure multiplicative band that is
closed under the cubic join operation $x\nabla y = x+y+yx-xyx-yxy.$ We show that
$\left( S,\cdot,\nabla\right) $ forms a pure skew lattice if and only if $S$
satisfies the polynomial identity $\left(xy-yx\right)^{2}z = z\left(xy-yx\right)^{2}$.
We also examine properties of pure skew lattices
in rings. 相似文献
999.
New heuristics for over-constrained flight to gate assignments 总被引:1,自引:0,他引:1
We consider the over-constrained Airport Gate Assignment Problem where the number of flights exceed the number of gates available, and where the objectives are to minimize the number of ungated flights and the total walking distances. The problem is formulated as a binary quadratic programming problem. We design a greedy algorithm and use a Tabu Search meta-heuristic to solve the problem. The greedy algorithm minimizes ungated flights while we devise a new neighbourhood search technique, the Interval Exchange Move, which allows us flexibility in seeking good solutions, especially when flight schedules are dense in time. Experiments conducted give good results. 相似文献
1000.
W Y Hung S Kucherenko N J Samsatli N Shah 《The Journal of the Operational Research Society》2004,55(8):801-813
In this paper, we present a new modelling approach for realistic supply chain simulation. The model provides an experimental environment for informed comparison between different supply chain policies. A basic simulation model for a generic node, from which a supply chain network can be built, has been developed using an object-oriented approach. This generic model allows the incorporation of the information and physical systems and decision-making policies used by each node. The object-oriented approach gives the flexibility in specifying the supply chain configuration and operation decisions, and policies. Stochastic simulations are achieved by applying Latin Supercube Sampling to the uncertain variables in descending order of importance, which reduces the number of simulations required. We also present a case study to show that the model is applicable to a real-life situation for dynamic stochastic studies. 相似文献