全文获取类型
收费全文 | 5167篇 |
免费 | 141篇 |
国内免费 | 11篇 |
专业分类
化学 | 3134篇 |
晶体学 | 118篇 |
力学 | 151篇 |
数学 | 721篇 |
物理学 | 1195篇 |
出版年
2022年 | 35篇 |
2021年 | 68篇 |
2020年 | 89篇 |
2019年 | 69篇 |
2018年 | 46篇 |
2017年 | 38篇 |
2016年 | 132篇 |
2015年 | 108篇 |
2014年 | 108篇 |
2013年 | 192篇 |
2012年 | 219篇 |
2011年 | 268篇 |
2010年 | 170篇 |
2009年 | 160篇 |
2008年 | 228篇 |
2007年 | 203篇 |
2006年 | 220篇 |
2005年 | 196篇 |
2004年 | 181篇 |
2003年 | 147篇 |
2002年 | 150篇 |
2001年 | 89篇 |
2000年 | 109篇 |
1999年 | 74篇 |
1998年 | 63篇 |
1997年 | 58篇 |
1996年 | 81篇 |
1995年 | 63篇 |
1994年 | 55篇 |
1993年 | 68篇 |
1992年 | 68篇 |
1991年 | 53篇 |
1990年 | 58篇 |
1989年 | 65篇 |
1988年 | 70篇 |
1987年 | 74篇 |
1986年 | 59篇 |
1985年 | 58篇 |
1984年 | 41篇 |
1983年 | 60篇 |
1982年 | 49篇 |
1981年 | 68篇 |
1980年 | 48篇 |
1979年 | 59篇 |
1978年 | 64篇 |
1977年 | 50篇 |
1976年 | 46篇 |
1975年 | 31篇 |
1974年 | 35篇 |
1973年 | 38篇 |
排序方式: 共有5319条查询结果,搜索用时 15 毫秒
21.
The kinetics of oxygen exchange are of primary importance for the application of titanates as fast resistive oxygen sensors.
The sensor’s conductivity is correlated with the oxygen partial pressure pO2 of the surrounding atmosphere: Due to oxygen surface transfer and subsequent diffusion of oxygen vacancies V
O
··
, a pO2 change gives rise to a conductivity change of the sample. While bulk diffusion usually occurs very fast, the surface transfer
reaction becomes the rate determining step for thin samples and for low temperatures. We have shown that in the case of acceptor
doped SrTiO3 the kinetics of the surface transfer reaction can be strongly influenced through stoichiometric changes brought about by
thin coatings of alkaline earth metal oxides (e.g. SrO). In contrast to the commonly used jump method (conductivity response
to a sudden pO2 change in the time domain), a model is presented which is based on the frequency-domain analysis of amplitude and phase shift
of the response signal obtained from a pO2 modulation in a fast kinetic measurement set-up. This method allows not only for measuring response times in the sub-millisecond
range but also for distinguishing between behaviour either controlled by volume diffusion or by surface transfer reaction.
Paper presented at the 9th EuroConference on Ionics, Ixia, Rhodes, Greece, Sept. 15 – 21, 2002. 相似文献
22.
Crystal Structure of the Zinc Amide Zn[N(SiMe3)2]2 X‐ray quality crystals of Zn[N(SiMe3)2]2 (monoclinic, P21/c) are obtained by sublimation of the zinc amide Zn[N(SiMe3)2]2 at —30 °C in vacuo (300 torr). According to the result of the X‐ray structural analysis, Zn[N(SiMe3)2]2 contains an almost linear N‐Zn‐N unit with two short N‐Zn bonds. 相似文献
23.
24.
Stephan Dahlke Gabriele Steidl Gerd Teschke 《Journal of Fourier Analysis and Applications》2004,10(5):507-539
This article is concerned with frame constructions on domains and manifolds. The
starting point is a unitary group representation which is square integrable modulo a suitable
subgroup and therefore gives rise to a generalized continuous wavelet transform. Then generalized
coorbit spaces can be defined by collecting all functions for which this wavelet transform
is contained in a weighted Lp-space. Moreover, we show that a judicious discretization of the
representation leads to an atomic decomposition and to Banach frames for these coorbit spaces. 相似文献
25.
O. Dumbrajs M. Thumm J. Pretterebner D. Wagner 《International Journal of Infrared and Millimeter Waves》1992,13(6):825-840
Mode conversion at discontinuities of an ordinary gyrotron cavity is examined. It is shown how the production of unwanted spurious modes can be reduced substantially by introducing smooth transition regions between the individual parts of the cavity. The cavity of the 140 GHz KfK gyrotron operating in the TE10,4 mode is used as an example. Cavity and adjacent tapered output waveguide are optimized as a single unit. 相似文献
26.
An improved method including extraction procedures is presented for the analysis of nucleotides in suspension-cultivated animal cells. Quantification was performed by ion-pair high-performance liquid chromatography after perchloric acid extraction. It was found that the amount of perchloric acid taken for extraction influenced the yield and that cell washing procedures caused deterioration of the analysis results for triphosphates. More than thirty nucleotides and sugar-nucleotides were separated within 25 min using a Supelcosil reversed-phase column (3 microns) with tetrabutylammonium hydrogensulphate as pairing agent and methanol-pH gradient elution. Cultivated hybridoma cells showed variations in intracellular nucleotide concentrations as well as relative amounts during different growth phases, which could reflect the physiological state of a cell culture. 相似文献
27.
Hyperfine Interactions - The YFe4Al8 and ErFe4Al8 intermetallics were studied by57Fe Mössbauer spectroscopy between 2 K and room temperature. The spectra are consistent with iron occupying 8f... 相似文献
28.
Kaon production is studied within the Giessen Boltzmann–Uehling–Uhlenbeck (GiBUU) model. Results are compared with experiment and with other models. The influence of the kaon potential on the kaon azimuthal distributions at SIS energies is considered. We also discuss the role of the many-body collisions at high-density phase of reaction. 相似文献
29.
Ivan Nunes da Silva Wagner Caradori do AmaralLucia Valeria de Arruda 《Applied Mathematical Modelling》2007
This paper presents an efficient approach based on recurrent neural network for solving nonlinear optimization. More specifically, a modified Hopfield network is developed and its internal parameters are computed using the valid subspace technique. These parameters guarantee the convergence of the network to the equilibrium points that represent an optimal feasible solution. The main advantage of the developed network is that it treats optimization and constraint terms in different stages with no interference with each other. Moreover, the proposed approach does not require specification of penalty and weighting parameters for its initialization. A study of the modified Hopfield model is also developed to analyze its stability and convergence. Simulation results are provided to demonstrate the performance of the proposed neural network. 相似文献
30.