全文获取类型
收费全文 | 558篇 |
免费 | 7篇 |
专业分类
化学 | 399篇 |
晶体学 | 5篇 |
力学 | 11篇 |
数学 | 50篇 |
物理学 | 100篇 |
出版年
2023年 | 4篇 |
2022年 | 7篇 |
2021年 | 6篇 |
2020年 | 14篇 |
2019年 | 12篇 |
2018年 | 7篇 |
2017年 | 9篇 |
2016年 | 9篇 |
2015年 | 13篇 |
2014年 | 11篇 |
2013年 | 25篇 |
2012年 | 35篇 |
2011年 | 44篇 |
2010年 | 18篇 |
2009年 | 15篇 |
2008年 | 38篇 |
2007年 | 34篇 |
2006年 | 43篇 |
2005年 | 44篇 |
2004年 | 35篇 |
2003年 | 24篇 |
2002年 | 22篇 |
2001年 | 4篇 |
2000年 | 7篇 |
1999年 | 2篇 |
1998年 | 5篇 |
1997年 | 2篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1971年 | 1篇 |
1968年 | 1篇 |
1967年 | 3篇 |
1964年 | 2篇 |
1962年 | 2篇 |
1961年 | 3篇 |
排序方式: 共有565条查询结果,搜索用时 15 毫秒
111.
Xiaolei Liu Hongtao Cui Wei Li Ning Song Fangyang Liu Gavin Conibeer Xiaojing Hao 《固体物理学:研究快报》2014,8(12):966-970
The effects of an ultrathin ZnO intermediate layer deposited at the CZTS/Mo interface on CZTS solar cell performance have been investigated in this work. The ZnO layer inhibits the generation of MoS2 layer and the formation of voids in the CZTS absorber. Consequently, the incorporation of this layer reduces the series resistance and increases the shunt resistance, which boosts photovoltaic conversion efficiency from 1.13% to 4.3%. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
112.
Gatehouse PD Thomas RW Robson MD Hamilton G Herlihy AH Bydder GM 《Magnetic resonance imaging》2004,22(8):1061-1067
BACKGROUND: We wished to assess the feasibility of imaging the knee with ultrashort TE (UTE) pulse sequences. SUBJECTS AND METHODS: Five volunteers and 16 patients were studied with UTE (TE=0.08 ms) sequences including later echoes. Conventional fat-suppressed images and difference images were also produced by subtracting a later echo from the first. Gadodiamide enhancement was used. RESULTS: High signal was obtained in tendons, ligaments, menisci and periosteum. Normal contrast enhancement was seen in these structures. Deep and superficial layers were seen in the articular cartilage. Cartilage defects were identified. The red zone could be differentiated from the white zone of the meniscus. Meniscal tears and degeneration were observed with low signal on subtraction images. Enhancement was seen within the anterior and posterior cruciate ligaments and associated scar tissue. CONCLUSION: Ultrashort TE imaging provides new options to visualize anatomy, manipulate conspicuity, observe contrast enhancement and demonstrate disease of the knee. 相似文献
113.
Carr G Poulsen M Klassen JL Hou Y Wyche TP Bugni TS Currie CR Clardy J 《Organic letters》2012,14(11):2822-2825
Microtermolides A (1) and B (2) were isolated from a Streptomyces sp. strain associated with fungus-growing termites. The structures of 1 and 2 were determined by 1D- and 2D-NMR spectroscopy and high-resolution mass spectrometry. Structural elucidation of 1 led to the re-examination of the structure originally proposed for vinylamycin (3). Based on a comparison of predicted and experimental (1)H and (13)C NMR chemical shifts, we propose that vinylamycin's structure be revised from 3 to 4. 相似文献
114.
The purpose of this study was to investigate the effect of parameter changes that can potentially lead to unreliable measurements in fat quantification. Chemical shift imaging was performed using spoiled gradient echo sequences with systematic variations in the following: two-dimensional/three-dimensional sequence, number of echoes, delta echo time, fractional echo factor, slice thickness, repetition time, flip angle, bandwidth, matrix size, flow compensation and field strength. Results indicated no significant (or significant but small) changes in fat fraction with parameter. The significant changes can be attributed to the known effects of T1 bias and two forms of noise bias. 相似文献
115.
Gavin Cullen Nicolas Greiner Gudrun Heinrich Gionata Luisoni Pierpaolo Mastrolia Giovanni Ossola Thomas Reiter Francesco Tramontano 《The European Physical Journal C - Particles and Fields》2012,72(3):1-32
We present the program package GoSam which is designed for the automated calculation of one-loop amplitudes for multi-particle processes in renormalisable quantum field theories. The amplitudes, which are generated in terms of Feynman diagrams, can be reduced using either D-dimensional integrand-level decomposition or tensor reduction. GoSam can be used to calculate one-loop QCD and/or electroweak corrections to Standard Model processes and offers the flexibility to link model files for theories Beyond the Standard Model. A standard interface to programs calculating real radiation is also implemented. We demonstrate the flexibility of the program by presenting examples of processes with up to six external legs attached to the?loop. 相似文献
116.
A central endeavor of thermodynamics is the measurement of free energy changes. Regrettably, although we can measure the free energy of a system in thermodynamic equilibrium, typically all we can say about the free energy of a nonequilibrium ensemble is that it is larger than that of the same system at equilibrium. Herein, we derive a formally exact expression for the probability distribution of a driven system, which involves path ensemble averages of the work over trajectories of the time-reversed system. From this we find a simple near-equilibrium approximation for the free energy in terms of an excess mean time-reversed work, which can be experimentally measured on real systems. With analysis and computer simulation, we demonstrate the accuracy of our approximations for several simple models. 相似文献
117.
The short syntheses of each of the mono-acetates of N-acetyl-D-neuraminic acid are reported. These are important molecules for studying the mechanism and function of enzymes which utilise Neu5Ac as a substrate. However, until now these molecules were not available as pure compounds and instead had to be studied as mixtures. Neu4,5Ac(2) and Neu5,8Ac(2) were synthesised from a common precursor in 2 and 4 steps respectively, while Neu2,4Ac(2) and Neu5,7Ac(2) were synthesised in 3 and 4 steps respectively from another common precursor. Both precursors could be easily prepared in 3 steps from Neu5Ac itself. Importantly, no scrambling of the anomeric stereochemistry was detected throughout the course of these syntheses. 相似文献
118.
N Esturau F Sánchez-Ferrando J A Gavin C Roumestand M A Delsuc T Parella 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2001,153(1):48-55
Undesirable temperature gradients in a NMR sample tube are usually generated by an inappropriate temperature regulation system. We have shown that such convection effects can greatly distort the measurement of translational self-diffusion coefficients. The use of sample spinning helps to minimize such undesirable effects by disruption of convection fluxes due to resulting Coriolis forces that have a strongly stabilizing effect on the conducting state of the system (J. Lounila et al., J. Magn. Reson. A 118, 50 (1996)). This simple trick allows the accurate measurement of diffusion coefficients for a wide range of temperatures and solvents without the need for a convection-compensated NMR pulse sequences or more sophisticated temperature control units. Experimental data obtained for some target compounds dissolved in several common deuterated solvents at different temperatures are reported and discussed. 相似文献
119.
Experiments have been conducted in a large shock tube to examine the four-wave shock reflection pattern, now known as Guderley
reflection (GR). The fourth wave, an expansion, is clearly identified, as is the supersonic patch behind the reflected wave.
A shocklet terminating the supersonic patch behind the reflected wave is identified, which forms a second triple point further
down the Mach stem. Evidence is presented showing the presence of more than one expansion wave and more than one shocklet,
thus indicating the existence of more than one supersonic patch. In order to distinguish between cases with a single patch
without the shocklet as originally proposed by Guderley and found in some computations, and the indications of a multi-patch
geometry found here, and also in other computations, this latter case is designated Guderley Mach reflection (GMR). Multi-exposure
images of the shock propagation superimposed on a single image frame enable estimates to be made of the strength of the major
waves, and it is shown that the reflected wave is very weak.
相似文献
120.
Here in, we described the synthesis of novel bisheterocycles imidazopyridine bearing xanthenedione by reacting various substituted 2-phenylimidazo [1,2-a] pyridine-3-carbaldehyde with cyclohexane-1,3-dione in gluconic acid aqueous solution (GAAS) via a tandem Knoevenagel followed by Michael, cyclization & tautomerization sequence. The use of GAAS in organic synthesis offers significant benefits like cost-effective, simple operation, reusable catalyst and green method. The reaction completed in 2–12?h to afford white stable solid compounds with very good yield. The structures of the compounds are confirmed by analyzing MS, IR, 1H NMR and 13C NMR spectra. Further, the structure of compound 3?h was confirmed by XRD analysis. 相似文献