全文获取类型
收费全文 | 968篇 |
免费 | 28篇 |
国内免费 | 5篇 |
专业分类
化学 | 691篇 |
晶体学 | 9篇 |
力学 | 13篇 |
数学 | 63篇 |
物理学 | 225篇 |
出版年
2022年 | 24篇 |
2021年 | 23篇 |
2020年 | 23篇 |
2019年 | 20篇 |
2018年 | 8篇 |
2017年 | 6篇 |
2016年 | 22篇 |
2015年 | 22篇 |
2014年 | 29篇 |
2013年 | 44篇 |
2012年 | 43篇 |
2011年 | 56篇 |
2010年 | 27篇 |
2009年 | 27篇 |
2008年 | 38篇 |
2007年 | 53篇 |
2006年 | 56篇 |
2005年 | 30篇 |
2004年 | 33篇 |
2003年 | 34篇 |
2002年 | 26篇 |
2001年 | 13篇 |
2000年 | 17篇 |
1999年 | 20篇 |
1998年 | 13篇 |
1997年 | 8篇 |
1996年 | 11篇 |
1995年 | 7篇 |
1994年 | 7篇 |
1993年 | 8篇 |
1992年 | 14篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1986年 | 17篇 |
1985年 | 18篇 |
1984年 | 8篇 |
1983年 | 10篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 14篇 |
1978年 | 7篇 |
1977年 | 8篇 |
1976年 | 6篇 |
1974年 | 5篇 |
1973年 | 7篇 |
1972年 | 6篇 |
1968年 | 5篇 |
1958年 | 23篇 |
排序方式: 共有1001条查询结果,搜索用时 15 毫秒
1.
We show that using ionic liquids as reagents in conjunction with microwave heating it is possible to prepare primary alkyl halides from the corresponding alcohols rapidly. Using ionic liquids as solvents in conjunction with microwave heating it is possible to prepare aryl nitriles from the corresponding aryl bromides or iodides. The scope and limitations of using microwave-promotion as a tool in these reactions is discussed. 相似文献
2.
The contribution of visualisation to mathematics and to mathematics education raises a number of questions of an epistemological nature. This paper is a brief survey of the ways in which visualisation is discussed in the literature on the philosophy of mathematics. The survey is not exhaustive, but pays special attention to the ways in which visualisation is thought to be useful to some aspects of mathematical proof, in particular the ones connected with explanation and justification. 相似文献
3.
4.
Hanna Sandler 《Geometriae Dedicata》1998,69(3):317-327
In this paper it is shown that one can choose an arbitrarily large number of inconjugate elements of the group Z/2Z*Z/2Z*Z/2Z which have the property that, under all representations of the group in SU(2,1) as a discrete complex hyperbolic ideal triangle group, the elements are hyperbolic and correspond to closed geodesics of equal length on the associated complex hyperbolic surface. This is an analogue of the geometric fact that the multiplicity of the length spectrum of a Riemann surface is never bounded or the equivalent algebraic phenomenon that an arbitrarily large number of conjugacy classes in a free group can have the same trace under all representations in SL(2,R ). 相似文献
5.
Stevenson NR Schubank RB Shin YM Amaudruz P Delheij PP Healey DC Jennings BK Ottewell DF Sheffer G Smith GR Wait GD Brack JT Feltham A Hanna M Johnson RR Rozon FM Sossi V Vetterli D Weber P Grion N Rui R Kohler M Ristinen RA Mathie EL Tacik R Yeomans M Gossett CA Wagner GJ 《Physical review letters》1990,65(16):1987-1990
6.
7.
S. A. Marei A. Badran E. Hanna 《Journal of Radioanalytical and Nuclear Chemistry》1979,53(1-2):155-161
The extraction of Tm with HDEHP from H2SO4, HCl and HBr is inversely proportional to the third power of the hydrogen ion concentration while the extraction is small with HDEHP, LA-2 and TBP from binary mixtures of acids. The extraction of both Eu and Tm with HDEHP from KI solutions decreases in the presence of small concentrations of H2SO4. The decrease is sharper in case of Eu leading to high separation factors between Eu and Tm from KI?H2SO4 mixtures. 相似文献
8.
Detection of the pesticide compound 1080 (sodium monofluoroacetate) using fluorine-19 nuclear magnetic resonance spectroscopy 总被引:2,自引:0,他引:2
Fluorine-19 nuclear magnetic resonance (19F NMR) spectroscopic measurements were used to determine the chemical nature and amounts of organofluorine in dosed meat baits. Earlier work implied that sodium monofluoroacetate (compound 1080) in meat baits was broken down into other organofluorine compounds such as fluorocitrate. No chemical evidence was found for such compounds. Only monofluoroacetate was detected in the prepared 1080 bait samples. Once the baits have aged, aqueous extraction fails to recover all the added 1080. Analysis using 19F NMR confirmed that the 1080 present in the aqueous extracts of the bait is recovered by Kramer's liquid chromatography method. It was shown here that the aqueous extracts do not recover all the 1080 in the meat bait. 相似文献
9.
Adam S. Plaziak Jaroslaw Spychala Hanna Wjtowicz Jerzy J. Langer Halina Thiel-Pawlicka Krzysztof Golankiewicz 《Journal of mass spectrometry : JMS》1992,27(11):1293-1298
Ortho-. meta- and para-isomers of N-(pyrimidin-4-yl)aminobenzoic acid and their methyl esters were investigated by electron impact mass Spectrometry. Their fragmentation was found to be strongly dependent on the position of the substituent in the aminobenzoic moiety. Two different kinds of ortho effect were studied and confirmed with the aid of deuterium-labelled derivatives. 相似文献
10.
Tanskanen H Khriachtchev L Lundell J Räsänen M 《The Journal of chemical physics》2004,121(17):8291-8298
We investigate the formation mechanism of HXeCCXeH in a Xe matrix. Our experimental results show that the HXeCCXeH molecules are formed in the secondary reactions involving HXeCC radicals. The experimental data on the formation of HXeCCXeH is fully explained based on the model involving the HXeCC+Xe+H-->HXeCCXeH reaction. This reaction is the first case when a noble-gas hydride molecule is formed from another noble-gas molecule. In addition, we investigate the (12)C/(13)C isotope effect on the vibrational properties of organo-noble-gas hydrides (HKrCCH, HXeCCH, HXeCC, and HXeCCXeH) in noble-gas matrixes. The present experimental results and ab initio calculations on carbon isotope shifts of the vibrational modes support the previous assignments of these molecules. Upon (12)C to (13)C isotope substitution, we observed a pronounced effect on the H-Kr stretching mode of HKrCCH (downshift of 1.0-3.6 cm(-1), depending on the matrix site) and a small anomalous shift (+0.1 cm(-1)) of the H-Xe stretching mode of HXeCCH and HXeCCXeH. 相似文献