全文获取类型
收费全文 | 35880篇 |
免费 | 2456篇 |
国内免费 | 1797篇 |
专业分类
化学 | 5343篇 |
晶体学 | 46篇 |
力学 | 1723篇 |
综合类 | 328篇 |
数学 | 5348篇 |
物理学 | 3798篇 |
综合类 | 23547篇 |
出版年
2024年 | 80篇 |
2023年 | 329篇 |
2022年 | 633篇 |
2021年 | 641篇 |
2020年 | 805篇 |
2019年 | 639篇 |
2018年 | 614篇 |
2017年 | 841篇 |
2016年 | 873篇 |
2015年 | 1062篇 |
2014年 | 1624篇 |
2013年 | 1739篇 |
2012年 | 1878篇 |
2011年 | 2115篇 |
2010年 | 1665篇 |
2009年 | 1931篇 |
2008年 | 1990篇 |
2007年 | 2407篇 |
2006年 | 2182篇 |
2005年 | 1996篇 |
2004年 | 1838篇 |
2003年 | 1725篇 |
2002年 | 1491篇 |
2001年 | 1266篇 |
2000年 | 1166篇 |
1999年 | 971篇 |
1998年 | 840篇 |
1997年 | 673篇 |
1996年 | 630篇 |
1995年 | 591篇 |
1994年 | 509篇 |
1993年 | 439篇 |
1992年 | 390篇 |
1991年 | 332篇 |
1990年 | 307篇 |
1989年 | 261篇 |
1988年 | 205篇 |
1987年 | 169篇 |
1986年 | 87篇 |
1985年 | 51篇 |
1984年 | 38篇 |
1983年 | 9篇 |
1982年 | 22篇 |
1981年 | 11篇 |
1980年 | 12篇 |
1979年 | 17篇 |
1978年 | 12篇 |
1977年 | 12篇 |
1976年 | 6篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
太阳能空调的可行性研究 总被引:3,自引:0,他引:3
对太阳能空调系统进行了定性分析 ,从环保、节能角度阐述了发展太阳能空调的优势所在。提出了太阳能空调将具有广阔的市场前景。 相似文献
52.
We obtain upper bounds for the tail distribution of the first nonnegative sum of a random walk and for the moments of the overshoot over an arbitrary nonnegative level if the expectation of jumps is positive and close to zero. In addition, we find an estimate for the expectation of the first ladder epoch. 相似文献
53.
Let G=(V(G),E(G)) be a graph. A (n,G, λ)‐GD is a partition of the edges of λKn into subgraphs (G‐blocks), each of which is isomorphic to G. The (n,G,λ)‐GD is named as graph design for G or G‐decomposition. The large set of (n,G,λ)‐GD is denoted by (n,G,λ)‐LGD. In this work, we obtain the existence spectrum of (n,P3,λ)‐LGD. © 2002 Wiley Periodicals, Inc. J Combin Designs 10: 151–159, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jcd.10008 相似文献
54.
In this work we study nonnegativity and positivity of a discrete quadratic functional with separately varying endpoints. We introduce a notion of an interval coupled with 0, and hence, extend the notion of conjugate interval to 0 from the case of fixed to variable endpoint(s). We show that the nonnegativity of the discrete quadratic functional is equivalent to each of the following conditions: The nonexistence of intervals coupled with 0, the existence of a solution to Riccati matrix equation and its boundary conditions. Natural strengthening of each of these conditions yields a characterization of the positivity of the discrete quadratic functional. Since the quadratic functional under consideration could be a second variation of a discrete calculus of variations problem with varying endpoints, we apply our results to obtain necessary and sufficient optimality conditions for such problems. This paper generalizes our recent work in [R. Hilscher, V. Zeidan, Comput. Math. Appl., to appear], where the right endpoint is fixed. 相似文献
55.
56.
F. S. de Aguiar L. B. Bernardes S. Goulart Rosa Jr. 《Journal of statistical physics》1991,64(3-4):673-682
Metastability in the ferromagneticp-state Potts model defined on the Cayley tree is discussed. It is shown that the sign of the boundary fieldH
s
determines the order of the transition as well as the stability of the low-temperature phase. Lowering the temperature withH
s
>0, a system withp<2 (p>2) will display a second (first)-order transition to a metastable (stable) phase. ForH
s
>0 a second (first)-order transition to a metastable (stable) phase occurs ifp>2 (p<2). In this case the system also has a residual entropy which is negative forp<2. 相似文献
57.
陈创新 《中山大学学报(自然科学版)》2005,44(6):45-48
提出了一种新的线性混叠信号的盲分离算法,该算法利用信号相互独立时其协方差矩阵的对角化特征作为分离准则,采用最速下降法进行分离.该算法对源信号和混叠矩阵没有过多要求且计算量不大,理论分析与仿真结果表明:该算法具有很好的分离效果. 相似文献
58.
气垫导轨在刚体转动惯量测定实验中的应用 总被引:1,自引:0,他引:1
本文介绍了一种测量刚体转动惯量的新方法。即把气垫导轨和刚体转动仪结合起来来测量刚体的转动惯量,使传统的气垫导轨实验和刚体转动惯量测定实验得以更新,提高了实验测量的精度,拓展了实验内容。 相似文献
59.
介绍了13~18世纪物理学史和科技史上曾名噪一时的第一类永动机的设计方案的破灭.第一类永动机幻梦破灭的历史引起了人们的反思与启示,有力地促进了19世纪中叶能量转化和守恒定律的确立. 相似文献
60.
Haifeng Yang Guangming XieTianguang Chu Long Wang 《Nonlinear Analysis: Theory, Methods & Applications》2006
In the paper, commuting and stable feedback design for switched linear systems is investigated. This problem is formulated as to build up suitable state feedback controller for each subsystem such that the closed-loop systems are not only asymptotically stable but also commuting each other. A new concept, common admissible eigenvector set (CAES), is introduced to establish necessary/sufficient conditions for commuting and stable feedback controllers. For second-order systems, a necessary and sufficient condition is established. Moreover, a parametrization of the CAES is also obtained. The motivation comes from stabilization of switched linear systems which consist of a family of LTI systems and a switching law specifying the switching between them, where if all the subsystems are stable and commuting each other, then the total system is stable under arbitrary switching. 相似文献