全文获取类型
收费全文 | 3526篇 |
免费 | 104篇 |
国内免费 | 24篇 |
专业分类
化学 | 2405篇 |
晶体学 | 25篇 |
力学 | 77篇 |
数学 | 602篇 |
物理学 | 545篇 |
出版年
2023年 | 18篇 |
2021年 | 26篇 |
2020年 | 40篇 |
2019年 | 52篇 |
2018年 | 40篇 |
2017年 | 30篇 |
2016年 | 69篇 |
2015年 | 61篇 |
2014年 | 99篇 |
2013年 | 193篇 |
2012年 | 155篇 |
2011年 | 186篇 |
2010年 | 125篇 |
2009年 | 117篇 |
2008年 | 169篇 |
2007年 | 158篇 |
2006年 | 152篇 |
2005年 | 147篇 |
2004年 | 119篇 |
2003年 | 109篇 |
2002年 | 112篇 |
2001年 | 63篇 |
2000年 | 73篇 |
1999年 | 45篇 |
1998年 | 58篇 |
1997年 | 45篇 |
1996年 | 51篇 |
1995年 | 49篇 |
1994年 | 43篇 |
1993年 | 46篇 |
1992年 | 47篇 |
1991年 | 54篇 |
1990年 | 37篇 |
1989年 | 45篇 |
1988年 | 51篇 |
1987年 | 41篇 |
1986年 | 52篇 |
1985年 | 52篇 |
1984年 | 56篇 |
1983年 | 39篇 |
1982年 | 34篇 |
1981年 | 41篇 |
1980年 | 51篇 |
1979年 | 42篇 |
1978年 | 39篇 |
1977年 | 36篇 |
1976年 | 31篇 |
1975年 | 30篇 |
1974年 | 22篇 |
1973年 | 22篇 |
排序方式: 共有3654条查询结果,搜索用时 375 毫秒
1.
Reza Kordnezhadian Bing-Yu Li Armir Zogu Dr. Joachim Demaerel Prof. Dr. Wim M. De Borggraeve Dr. Ermal Ismalaj 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(60):e202201491
Pentafluorosulfanyl (SF5)-containing compounds and corresponding analogs are a highly valuable class of fluorine-containing building blocks owing to their unique properties. The reason for that is the set of peculiar and tremendously beneficial characteristics they can impart on molecules once introduced onto them. Despite this, their application in distinct scientific fields remains modest, given the extremely harsh reaction conditions needed to access such compounds. The recent synthetic approaches via S−F, and C−SF5 bond formation as well as the use of SF5-containing building blocks embody a “stairway-to-heaven” loophole in the synthesis of otherwise-inaccessible chemical scaffolds only a few years ago. Herein, we report and evaluate the properties of the SF5 group and analogs, by summarizing synthetic methodologies available to access them as well as following applications in material science and medicinal chemistry since 2015. 相似文献
2.
3.
Summary We present an approximation method of a space-homogeneous transport equation which we prove is convergent. The method is very promising for numerical computation. Comparison of a numerical computation with an exact solution is given for the Master equation. 相似文献
4.
Nuclear Magnetic Resonance (NMR) was used to investigate the extrusion behaviour of PTFE pastes in a ram extruder. By means
of 1H-NMR imaging (MRI) it is possible to determine the local proton density and therefore, the local fluid concentration. The
19F-MRI provides the local solid concentration. Thus the local saturation and the local porosity can be calculated with the
information of the local fluid and solid concentration. Furthermore displacement profiles can be derived from NMR images by
means of correlation techniques without any preparation or marking of the pastes.
Received: 8 May 2000 Accepted: 1 May 2001 相似文献
5.
Signed graphs for portfolio analysis in risk management 总被引:1,自引:0,他引:1
Harary Frank; Lim Meng-Hiot; Wunsch Donald C. 《IMA Journal of Management Mathematics》2002,13(3):201-210
We introduce the notion of structural balance for signed graphsin the context of portfolio analysis. A portfolio of securitiescan be represented as a signed graph with the nodes denotingthe securities and the edges representing the correlation betweenthe securities. With signed graphs, the characteristics of aportfolio from a risk management perspective can be uncoveredfor analysis purposes. It is shown that a portfolio characterizedby a signed graph of positive and negative edges that is structurallybalanced is characteristically more predictable. Investors whoundertake a portfolio position with all positively correlatedsecurities do so with the intention to speculate on the upside(or downside). If the portfolio consists of negative edges andis balanced, then it is likely that the position has a hedgingdisposition within it. On the other hand, an unbalanced signedgraph is representative of an investment portfolio which ischaracteristically unpredictable. 相似文献
6.
Matrix extensions and eigenvalue completions, the generic case 总被引:2,自引:0,他引:2
William Helton Joachim Rosenthal Xiaochang Wang 《Transactions of the American Mathematical Society》1997,349(8):3401-3408
In this paper we provide new necessary and sufficient conditions for the so-called eigenvalue completion problem.
7.
8.
9.
For the first time a comparative study of holographic recording in planarly oriented films of nematic and cholesteric azobenzene-containing polymers was performed. The influence of temperature and light intensity on the values of diffraction efficiencies of holographic gratings was investigated. The kinetics of grating relaxation at different temperatures was studied. It was shown that the helical supramolecular structure of cholesteric copolymer causes a significant decrease of the diffraction efficiency in comparison with the one observed for the nematic state of the homopolymer. 相似文献
10.