全文获取类型
收费全文 | 990篇 |
免费 | 49篇 |
国内免费 | 3篇 |
专业分类
化学 | 604篇 |
晶体学 | 5篇 |
力学 | 43篇 |
数学 | 213篇 |
物理学 | 177篇 |
出版年
2023年 | 11篇 |
2022年 | 17篇 |
2021年 | 19篇 |
2020年 | 23篇 |
2019年 | 13篇 |
2018年 | 18篇 |
2017年 | 20篇 |
2016年 | 27篇 |
2015年 | 34篇 |
2014年 | 34篇 |
2013年 | 59篇 |
2012年 | 83篇 |
2011年 | 90篇 |
2010年 | 55篇 |
2009年 | 41篇 |
2008年 | 83篇 |
2007年 | 58篇 |
2006年 | 54篇 |
2005年 | 51篇 |
2004年 | 40篇 |
2003年 | 38篇 |
2002年 | 38篇 |
2001年 | 14篇 |
2000年 | 13篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1997年 | 6篇 |
1996年 | 6篇 |
1995年 | 6篇 |
1994年 | 8篇 |
1993年 | 7篇 |
1992年 | 6篇 |
1991年 | 2篇 |
1987年 | 2篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 9篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1973年 | 2篇 |
1969年 | 1篇 |
1938年 | 1篇 |
1931年 | 2篇 |
1926年 | 1篇 |
1900年 | 1篇 |
1886年 | 2篇 |
1883年 | 1篇 |
排序方式: 共有1042条查询结果,搜索用时 15 毫秒
51.
Magrez A Seo JW Mikó C Hernadi K Forró L 《The journal of physical chemistry. B》2005,109(20):10087-10091
Multiwalled carbon nanotubes (MWCNTs) were grown by chemical vapor deposition by applying C(2)H(2) fluxed over Fe(1)(-x)Co(x) catalyst supported by alkaline earth carbonate. Detailed investigations of the chemical process occurring prior and during the growth allowed us a significant improvement of the nanotube production rate and quality. We observed a strong influence of the catalyst stoichiometry on the carbon deposition rate and the nanotube characteristics. We also found evidence for the active role of the support in the growth process, which is explained by the decomposition of the carbonate at the growth temperature. Using the optimized parameters obtained from our study performed in a fixed bed furnace, we could improve the production rate to about 500 g/day of purified MWCNTs in our large-scale rotary tube furnace. 相似文献
52.
Arbouet A Christofilos D Del Fatti N Vallée F Huntzinger JR Arnaud L Billaud P Broyer M 《Physical review letters》2004,93(12):127401
The absorption of a single isolated metal cluster is directly measured using a novel far-field optical technique based on modulation of its position. Single gold nanoparticles with average diameters down to 5 nm, dispersed on a transparent substrate, are optically detected and their absolute absorption cross section determined. 相似文献
53.
54.
Femtosecond laser direct writing is employed for the fabrication of buried tubular waveguides in bulk poly(methyl methacrylate). A novel technique using selective chemical etching is presented to resolve the two-dimensional refractive-index profile of the fabrication structures. End-to-end coupling in the waveguides reveals a near-field intensity distribution that results from the superimposition of several propagating modes with different azimuthal symmetries. Mode analysis of the tubular waveguides is performed using the finite-difference method, and the possible propagating mode profiles are compared with the experimental data. 相似文献
55.
Henry-dit-Quesnel A Toupet L Pommelet JC Lequeux T 《Organic & biomolecular chemistry》2003,1(14):2486-2491
The synthesis of difluoromethylphosphonates is becoming difficult due to environmental protective laws restricting the use of HCFCs and CFCs as starting chemicals. To circumvent this limitation, we report the preparation of a thioether as a new source of the lithiodifluoromethylphosphonate. This methodology avoiding the use of HCFCs involves a selective fluorination of sulfide followed by a thiaphilic addition of an organometallic reagent, which offers an alternative route to obtain phosphonodifluoromethyl carbanion. A contrasted reactivity, due to a medium effect, was also noted which allows addition of a wide range of electrophiles including nitroalkenes and DMF to thioethers. 相似文献
56.
The cyclization reactions of the 4-pentenyl, 5-hexenyl, 6-heptenyl, and 7-octenyl fluorinated and ether radicals have been studied by a hybrid Hartree-Fock density functional method. The reliability of this approach has been confirmed in agreement with experimental data and post-Hartree-Fock projected M?ller-Plesset second-order method. The analysis of the theoretical results shows that two factors are crucial for the determination of the regiochemistry and the reactivity of these reactions. The first factor is the ability of the starting radical to have a stable conformation in position to form the transition state, and the second one is the enthalpic effect of the reaction through the stability of the resulting cyclized radical. It should be pointed out that these factors are not linked to the polarity of the radicals due to the presence of CF2 groups. 相似文献
57.
P. Billaud J.-R. Huntzinger E. Cottancin J. Lermé M. Pellarin L. Arnaud M. Broyer N. Del Fatti F. Vallée 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):271-274
The extinction spectrum of single silver nanoparticles
with size ranging from 20 to 80 nm is investigated with the spatial
modulation spectroscopy technique using either a tunable laser or a white
lamp as the broadband source. Results are in good agreement with the
prediction of the Mie theory, permitting to extract the nanoparticle size
from the measured absolute value of the optical extinction cross-section. In
contrast, the deduced refractive index of the nanoparticle environment and
the reduction of the electron mean free path show a large dependence on the
precise value of the bulk silver dielectric function. 相似文献
58.
We address the problem of degree of polarization (DOP) estimation in images limited by additive Gaussian detector noise. We derive and analyze the probability density function (PDF) of the pixelwise DOP estimate, which is shown to have significantly different statistical properties than when noise is Gamma distributed (speckle). We then determine the Cramer-Rao Lower Bound and the maximum likelihood estimator of the DOP. We deduce from this study practical solutions for characterizing and reducing the noise in these images. 相似文献
59.
Sébastien DegorceFrédéric H. Jung Craig S. Harris Patrice KozaJonathan Lecoq Arnaud Stevenin 《Tetrahedron letters》2011,52(50):6719-6722
The synthesis of differentially-substituted 3,5-bis(arylamino)pyrazoles has not yet been documented. During our investigation, we managed to develop a novel, entirely combinatorial synthesis of 3,5-bis(arylamino)pyrazoles relying on a simple one-pot two-step operation. 相似文献
60.
Julien Amalric Claude Poleunis Arnaud Delcorte Jacqueline Marchand-Brynaert 《Surface science》2012,606(13-14):1071-1077
Chalcogenide glasses are useful optic materials that find applications in infrared spectroscopy, sensors and thermal imaging. A route for direct surface modification of such glasses with organic layers has been investigated by static Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The GAS (germanium–arsenic–selenium) glasses are modified by deposition followed by UV-irradiation of disulfide- or/and silane-functionalized organic molecules. SIMS analysis shows the characteristic fragments of the grafted molecules and organic–inorganic fragments which prove unambiguously the binding mode to the surface: disulfides, after S–S cleavage, are linked to arsenic and selenium; triethoxysilanes bind exclusively to oxidized germanium. The successive grafting of disulfide and silane compounds on the same substrate (IG2 glass with 33% of Ge) affords a “mixed” organic layer on the glass surface. From water contact angle measurements and X-ray Photo-electron Spectroscopy (XPS), the coverage density is not significantly improved comparatively to the “non-mixed” layers. However, the grafting of both types of molecules allows to reach a more homogeneous coverage. 相似文献