全文获取类型
收费全文 | 10019篇 |
免费 | 1134篇 |
国内免费 | 678篇 |
专业分类
化学 | 2683篇 |
晶体学 | 34篇 |
力学 | 1439篇 |
综合类 | 188篇 |
数学 | 4732篇 |
物理学 | 2755篇 |
出版年
2024年 | 18篇 |
2023年 | 84篇 |
2022年 | 163篇 |
2021年 | 171篇 |
2020年 | 252篇 |
2019年 | 230篇 |
2018年 | 238篇 |
2017年 | 288篇 |
2016年 | 317篇 |
2015年 | 267篇 |
2014年 | 431篇 |
2013年 | 608篇 |
2012年 | 424篇 |
2011年 | 513篇 |
2010年 | 478篇 |
2009年 | 548篇 |
2008年 | 641篇 |
2007年 | 654篇 |
2006年 | 587篇 |
2005年 | 561篇 |
2004年 | 446篇 |
2003年 | 420篇 |
2002年 | 508篇 |
2001年 | 350篇 |
2000年 | 305篇 |
1999年 | 261篇 |
1998年 | 289篇 |
1997年 | 212篇 |
1996年 | 236篇 |
1995年 | 200篇 |
1994年 | 158篇 |
1993年 | 139篇 |
1992年 | 114篇 |
1991年 | 96篇 |
1990年 | 66篇 |
1989年 | 58篇 |
1988年 | 59篇 |
1987年 | 53篇 |
1986年 | 53篇 |
1985年 | 56篇 |
1984年 | 43篇 |
1983年 | 20篇 |
1982年 | 48篇 |
1981年 | 43篇 |
1980年 | 26篇 |
1979年 | 32篇 |
1978年 | 22篇 |
1977年 | 7篇 |
1976年 | 13篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
《Operations Research Letters》2022,50(3):274-280
The minimum k-enclosing ball problem seeks the ball with smallest radius that contains at least k of m given points. This problem is NP-hard. We present a branch-and-bound algorithm on the tree of the subsets of k points to solve this problem. Our method is able to solve the problem exactly in a short amount of time for small and medium sized datasets. 相似文献
4.
Simultaneous quantitative determination of 20 active components in the traditional Chinese medicine formula Zhi‐Zi‐Da‐Huang decoction by liquid chromatography coupled with mass spectrometry: application to study the chemical composition variations in different combinations
下载免费PDF全文
![点击此处可从《Biomedical chromatography : BMC》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Zheng Tang Ran Yin Kaishun Bi Heyun Zhu Fei Han Kelin Chen Fenrong Wang 《Biomedical chromatography : BMC》2015,29(9):1406-1414
5.
Natalia L. Calvo Sebastian O. SimonettiRubén M. Maggio Teodoro S. Kaufman 《Analytica chimica acta》2015
Exposure of cimetidine (CIM) to dry heat (160–180 °C) afforded, upon cooling, a glassy solid containing new and hitherto unknown products. The kinetics of this process was studied by a second order chemometrics-assisted multi-spectroscopic approach. Proton and carbon-13 nuclear magnetic resonance (NMR), as well as ultraviolet and infrared spectroscopic data were jointly used, whereas multivariate curve resolution with alternating least squares (MCR-ALS) was employed as the chemometrics method to extract process information. It was established that drug degradation follows a first order kinetics. 相似文献
6.
We give a sheaf theoretic interpretation of Potts models with external magnetic field, in terms of constructible sheaves and their Euler characteristics. We show that the polynomial countability question for the hypersurfaces defined by the vanishing of the partition function is affected by changes in the magnetic field: elementary examples suffice to see non-polynomially countable cases that become polynomially countable after a perturbation of the magnetic field. The same recursive formula for the Grothendieck classes, under edge-doubling operations, holds as in the case without magnetic field, but the closed formulae for specific examples like banana graphs differ in the presence of magnetic field. We give examples of computation of the Euler characteristic with compact support, for the set of real zeros, and find a similar exponential growth with the size of the graph. This can be viewed as a measure of topological and algorithmic complexity. We also consider the computational complexity question for evaluations of the polynomial, and show both tractable and NP-hard examples, using dynamic programming. 相似文献
7.
8.
In this paper, we consider a viscoelastic wave equation of variable coefficients in the presence of past history with nonlinear damping and delay in the internal feedback and dynamic boundary conditions. Under suitable assumptions, we establish an explicit and general decay rate result without imposing restrictive assumption on the behavior of the relaxation function at infinity by Riemannian geometry method and Lyapunov functional method. 相似文献
9.
HIRFL–CSR加速器中束流与真空中剩余气体的碰撞损失 总被引:1,自引:1,他引:0
研究了重离子加速器中束流与真空中剩余气体的碰撞损失过程和碰撞截面,在依据大量实验数据的基础上,提出了一组计算离子一原子的电荷交换截面的经验公式.以兰州重离子加速器HDRFL及冷却储存环CSR为例,给出了依据碰撞截面的公式计算束流在加速器真空中的传输效率的方法,并计算了在不同真空度下HIRFL的ECR源轴向注入束运线、注入器SFC、前束运线、主加速器SSC和后束运线等不同加速阶段及CSR的传输效率,并提出合理的真空度要求.HIRFL的真空分布测量和束流的损失测量证明了该计算方法的可靠性. 相似文献
10.
I. L. Eremenko M. A. Golubnichaya S. E. Nefedov A. A. Sidorov D. A. Nesterenko N. P. Konovalova L. M. Volkova L. T. Eremenko 《Russian Chemical Bulletin》1997,46(9):1595-1598
Thetrans-[Pt(NC5H4C(O)NHC2H4ONO2)2Cl2] complex (2) was prepared by the reaction of nicorandyl (N-nitroethoxynicotinamide), which is widely used in cardiology, with K2PtCl4 in water. The structure of2 was established by X-ray structural analysis. It was found that complex2 exhibits high antitumor activity, in particular, antimetastatic activity, unlike the analogous CuII complex with bromine atoms.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1672–1675, September, 1997. 相似文献