全文获取类型
收费全文 | 241509篇 |
免费 | 16746篇 |
国内免费 | 642篇 |
专业分类
化学 | 152339篇 |
晶体学 | 3357篇 |
力学 | 10266篇 |
综合类 | 5篇 |
数学 | 23533篇 |
物理学 | 69397篇 |
出版年
2023年 | 4444篇 |
2022年 | 2482篇 |
2021年 | 3941篇 |
2020年 | 6237篇 |
2019年 | 4094篇 |
2018年 | 4962篇 |
2017年 | 3169篇 |
2016年 | 9043篇 |
2015年 | 7526篇 |
2014年 | 8295篇 |
2013年 | 13890篇 |
2012年 | 10106篇 |
2011年 | 9619篇 |
2010年 | 9209篇 |
2009年 | 8962篇 |
2008年 | 8843篇 |
2007年 | 8697篇 |
2006年 | 7802篇 |
2005年 | 6931篇 |
2004年 | 6454篇 |
2003年 | 5679篇 |
2002年 | 5503篇 |
2001年 | 6447篇 |
2000年 | 4944篇 |
1999年 | 3806篇 |
1998年 | 3049篇 |
1997年 | 3087篇 |
1996年 | 2833篇 |
1995年 | 2711篇 |
1994年 | 2522篇 |
1993年 | 2511篇 |
1992年 | 2748篇 |
1991年 | 2723篇 |
1990年 | 2633篇 |
1989年 | 2438篇 |
1988年 | 2516篇 |
1987年 | 2499篇 |
1985年 | 3004篇 |
1984年 | 3267篇 |
1983年 | 2693篇 |
1982年 | 2866篇 |
1981年 | 2848篇 |
1980年 | 2732篇 |
1979年 | 2815篇 |
1978年 | 2906篇 |
1977年 | 2974篇 |
1976年 | 3056篇 |
1975年 | 2847篇 |
1974年 | 2820篇 |
1973年 | 2884篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The variation of the electroactivity range with composition of water+ sulphuric acid mixtures has been studied. It is shown that ferrocene provides a reference potential independent of solvent at low H2SO4 contents while polynuclear hydrocarbons fulfill the same function at high H2SO4 contents. Water+H2SO4 mixtures become more oxidizing (reduction limit) and less reducing (oxidation limit) when the H2SO4 concentration increases. 相似文献
992.
The number of products and the H2/CH4 ratio obtained from the flow pyrolyses of (CH3)3GeH and (CH3)3SiH were very different. The (CH3)3GeH decomposition is consistent with the following mechanism:
The pyrolysis of (CH3)3SiH was found to be much more complex, presumably due to the formation of silicon-carbon double bonded intermediates and the (CH3)2Si(H)CH2 radical. We also present data which supports the presence of a H atom chain sequence during this pyrolysis. 相似文献
Full-size image
993.
3-methylenebicyclo[2,2,1]heptane-2,6-carbolactone (previously incorrectly claimed) has now been prepared and converted to the 3-oxo-lactone. Some 3-hydroxy-bicyclo-[2,2,1]heptane-2,6-carbolactones have been prepared and their rates of oxidation with chromic acid determined. The results do not support a theory about the mechanism of oxidation, involving a dipolar interaction from the lactone. 相似文献
994.
H. D. Sommer und F. Umland 《Fresenius' Journal of Analytical Chemistry》1977,285(5):359-361
Zusammenfassung Alizarin S und seine 11-Metallchelate lassen sich an der Quecksilbertropfelektrode reduzieren. Aus der Beeinflussung der diffusionskontrollierten und der Adsorptionsstufe durch die Chelatbildung lassen sich Aussagen über die Konstitution und Ladung der adsorbierten Chelate machen: Beryllium wird in peri-, Aluminium und Gallium werden in ortho-Stellung des Alizarinmoleküls gebunden. Die 11-Chelate des Be und Al sind ungeladen. Das Ga-Chelat ist negativ geladen und enthält offensichtlich zusätzliche anionische Liganden.Wir danken der Deutschen Forschungsgemeinschaft, Bonn-Bad Godesberg, dem Minister für Wissenschaft und Forschung des Landes Nordrhein-Westfalen, Landesamt für Forschung, sowie dem Verband der Chemischen Industrie, Fonds der Chemie, für Sachbeihilfen. 相似文献
995.
The crystals of Ni0,33Mo3Se4, are triclinic, space group , with two formula units in a cell: a = 6,727 (9) Å, b = 6,582 (11) Å, c = 6,751 (6) Å, α = 90.61° (10), β = 92.17° (10), γ = 90.98° (12.) The structure was solved by analogy with Mo3Se4 and refined by a full-matrix least squares program to R = 0,093 for 822 independent reflexions. The channels present in Mo3Se4 are occupied by Ni so that Ni0,33Mo3Se4 is always a metallic compound. 相似文献
996.
The adhesive secreted by the barnacle, Balanus eburneus, has been demonstrated to contain two hexosamines, glucosamine and galactosamine. Degradation of the hexosamines during hydrolysis of the adhesive appears to be the reason why previous studies of the adhesive have indicated the absence of hexosamines, or the presence of only one hexosamine. 相似文献
997.
D. Klockow 《Fresenius' Journal of Analytical Chemistry》1963,198(3):285
Ohne Zusammenfassung 相似文献
998.
Direct semi-automatic and automatic derivative potentiometric EDTA procedures for the determination of calcium and/or magnesium with a calcium-selective electrode are described. Calcium is titrated in the presence of magnesium at pH 12.0 and the total calcium and magnesium is determined at pH 9.7. Calcium in the range 1-8 mg and magnesium in the range 0.7-5 mg are determined semi-automatically with average errors of about 0.2 and 0.3% respectively and automatically with average errors of 0.4 and 0.7%. Titration times vary from a few seconds to a few minutes. 相似文献
999.
D. I. Zhukhovitskii 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2006,80(9):1489-1497
The potential of the interaction of an alkali metal with a planar metal surface was calculated by solving a two-dimensional Schrödinger equation. The potential energy of the valence electron of the atom was derived from a model pseudopotential based on the image potential. It was demonstrated that the potential energy curve for the interaction of an alkali metal atom with the surface of a heavier alkali metal has a minimum at a certain distance from the surface, a feature that gives rise to equilibrium states of levitating atoms. 相似文献
1000.
A. L. Podkorytov S. R. Kudakaeva E. V. Sokolova S. A. Shtin D. N. Ashikhmin 《Russian Journal of Inorganic Chemistry》2006,51(1):46-50
The main features of the synthesis of (Pb1-x
Srx)2Nb2O7 and (Pb1-x
Bax)2Nb2O7 pyrochlore solid solutions were determined using isothermal thermogravimetry in tandem with formal-kinetic analysis. The
stability and electron-transport properties of the triple niobates were studied, which allowed us to test them as electrode-active
materials for membranes in ion-selective electrodes (ISEs). 相似文献