全文获取类型
收费全文 | 938篇 |
免费 | 25篇 |
国内免费 | 8篇 |
专业分类
化学 | 632篇 |
晶体学 | 10篇 |
力学 | 21篇 |
数学 | 89篇 |
物理学 | 219篇 |
出版年
2023年 | 5篇 |
2022年 | 31篇 |
2021年 | 34篇 |
2020年 | 14篇 |
2019年 | 29篇 |
2018年 | 15篇 |
2017年 | 16篇 |
2016年 | 27篇 |
2015年 | 27篇 |
2014年 | 49篇 |
2013年 | 45篇 |
2012年 | 65篇 |
2011年 | 59篇 |
2010年 | 48篇 |
2009年 | 43篇 |
2008年 | 55篇 |
2007年 | 66篇 |
2006年 | 58篇 |
2005年 | 39篇 |
2004年 | 41篇 |
2003年 | 20篇 |
2002年 | 25篇 |
2001年 | 10篇 |
2000年 | 13篇 |
1999年 | 15篇 |
1998年 | 8篇 |
1997年 | 19篇 |
1996年 | 9篇 |
1995年 | 7篇 |
1994年 | 17篇 |
1993年 | 10篇 |
1992年 | 9篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 5篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有971条查询结果,搜索用时 562 毫秒
21.
A. Kratzer K. Mutzbauer S. Henneberger G. M. Kalvius O. Hartmann R. Wäppling H. -H. Klauß M. A. C. De Melo F. J. Litterst Th. Stammler 《Hyperfine Interactions》1994,87(1):1055-1061
The high pressureSR spectrometer [1] formerly located at CERN has been transferred to theE1-beamline at PSI and put back into operation with only minor modifications. The essential features of the high pressure apparatus are described below. The instrument covers a pressure range up to 0.7 GPa which can be extended to 1.4 GPa depending on the design of the high pressure cell. First measurements at PSI were successfully carried out with a single crystalline sample of Gd metal. New developments in high pressure cell design are presented. They are expected to further improve the signal/background ratio and to extend the pressure range to 1 GPa. One type of cell will allow temperatures above 380 K.This work was supported by the German Federal Minister for Research and Technology (Bundesminister für Forschung und Technologie [BMFT]) under Contract Nr. 03KA2-TUM-4 and 03SE3STU. 相似文献
22.
O. Hartmann E. Karlsson R. Wäppling L. Asch S. Henneberger G. M. Kalvius A. Kratzer H. -H. Klauß F. J. Litterst M. A. C. De Melo 《Hyperfine Interactions》1994,85(1):251-258
We have studied the muon precession frequency in a ferromagnetic single crystal of Gd metal. The overall features of our findings are compatible with earlier results on polycrystalline material. In the temperature region between 245 and 220 K where the Gd magnetization starts to turn away from the c-axis, we observe an increase in the muon depolarization rate, and a complex precession signal which can be separated into two frequency components meaning that spin turning does not occur simultaneously in different parts of the sample (domains). From these more detailed data follows that previously obtained values forB
fc andB
dip can not both be correct. Two explanations for our new result are possible: EitherB
fc undergoes a change around 230 K which is directly coupled to the spin turning angle, or the value of the dipolar field contribution used in the earlier evaluation is too low. This imposes some uncertainty as to the value of the angle at the onset of spin turning derived fromSR frequencies. 相似文献
23.
24.
25.
Teresa M V D Pinho e Melo Cláudia S J Lopes António M d'A Rocha Gonsalves Ana M Beja José A Paix?o Manuela R Silva Luiz Alte da Veiga 《The Journal of organic chemistry》2002,67(1):66-71
Nucleophilic substitution reactions of 2-halo-2H-azirines 1a, 1b, 1d, and 1e with potassium phthalimide and aniline allowed the preparation of new substituted 2H-azirines 2-5. The reactions of 2-bromo-2H-azirine 1a with methylamine led to the synthesis of alpha-diimines 7 and 8. 2-Halo-2H-azirines were also established as building blocks for the synthesis of a range of heterocyclic compounds, namely, quinoxalines 10a-10d, 3-oxazoline 14, and 2H-[1,4]oxazines 18 and 20. X-ray crystal structures of alpha-diimine 7, 3-oxazoline 14, and 2H-[1,4]oxazine 18 are reported. 相似文献
26.
A fast system for steel analysis is described. Immediately after collection, the solidified sample is polished and placed on a small electrochemical dissolution unit. The dissolution step is accomplished in a few seconds, and the dissolved material is passed directly “on line” to a flow-injection manifold. The feasibility of the approach is demonstrated by determining soluble aluminium in steels (0.01–0.13% w/w) spectrophotometrically. Dissolution conditions such as current density, electrolysis duration, composition and flow rate of the electrolyte carrier stream are described. The proposed system is very stable and the consumption of reagents is low; 20–40 samples per hour can be handled. The results compare well with the values for reference standard steels. 相似文献
27.
Laura M. Bruno José L. de Lima Filho Eduardo H. de M. Melo Heizir F. de Castro 《Applied biochemistry and biotechnology》2004,113(1-3):189-199
Mucor miehei lipase was immobilized on magnetic polysiloxane-polyvinyl alcohol particles by covalent binding with high activity recovered.
The performance of the resulting immobilized biocatalyst was evaluated in the synthesis of flavor esters using heptane as
solvent. The impact on reaction rate was determined for enzyme concentration, molar ratio of the reactants, carbon chain length
of the reactants, and alcohol structure. Ester synthesis was maximized for substrates containing excess acyl donor and lipase
loading of 25 mg/mL. The biocatalyst selectivity for the carbon chain length was found to be different concerning the organic
acids and alcohols. High reaction rates were achieved for organic acids with 8 or 10 carbons, whereas increasing the alcohol
carbon chain length from 4 to 8 carbons gave much lower esterification yields. Optimal reaction rate was determined for the
synthesis of butyl caprylate (12 carbons). Esterification performance was also dependent on the alcohol structure, with maximum
activity occurring for primary alcohol. Secondary and tertiary alcohols decreased the reaction rates by more than 40%. 相似文献
28.
29.
30.
Érika Pinto Marinho A. G. Souza Danniely S. de Melo Iêda M. G. Santos Dulce M. A. Melo Walquíria J. da Silva 《Journal of Thermal Analysis and Calorimetry》2007,87(3):801-804
Because
of their electrical, magnetic and catalytic properties rare earth and transition
metal mixed oxides are important compounds. Lanthanum chromites have been
extensively used as solid oxide fuel cell (SOFC) interconnect materials. In
this work, lanthanum chromites partially substituted by alkaline earth metals
were synthesized by the urea combustion process. TG and DSC techniques were
used to evaluate the presence of the organic material in the powder after
reaction on the hot plate. The powders were calcinated at 900°C and characterized
by XRD and SEM. The results show that the particles have nanometric dimensions
and the perovskite structure was formed. 相似文献