全文获取类型
收费全文 | 1343篇 |
免费 | 64篇 |
国内免费 | 6篇 |
专业分类
化学 | 876篇 |
晶体学 | 10篇 |
力学 | 17篇 |
数学 | 179篇 |
物理学 | 331篇 |
出版年
2023年 | 6篇 |
2022年 | 20篇 |
2021年 | 32篇 |
2020年 | 27篇 |
2019年 | 29篇 |
2018年 | 15篇 |
2017年 | 23篇 |
2016年 | 35篇 |
2015年 | 42篇 |
2014年 | 50篇 |
2013年 | 76篇 |
2012年 | 88篇 |
2011年 | 89篇 |
2010年 | 51篇 |
2009年 | 68篇 |
2008年 | 101篇 |
2007年 | 81篇 |
2006年 | 61篇 |
2005年 | 47篇 |
2004年 | 52篇 |
2003年 | 42篇 |
2002年 | 59篇 |
2001年 | 29篇 |
2000年 | 38篇 |
1999年 | 30篇 |
1998年 | 19篇 |
1997年 | 11篇 |
1996年 | 17篇 |
1995年 | 13篇 |
1994年 | 13篇 |
1993年 | 17篇 |
1992年 | 13篇 |
1991年 | 11篇 |
1990年 | 13篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 10篇 |
1986年 | 9篇 |
1985年 | 14篇 |
1984年 | 10篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1978年 | 2篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1941年 | 2篇 |
1931年 | 2篇 |
排序方式: 共有1413条查询结果,搜索用时 15 毫秒
11.
A. González Arias C. Torres C. de
Francisco J. M. Muñoz P. Hernández
Gómez O. Alejos O. Montero J. I. Iñiguez 《Journal of Thermal Analysis and Calorimetry》2006,86(1):195-198
The article discusses theory and experiment about the measurement of
defect concentration in Ti-substituted yttrium iron garnet by means of thermogravimetry
techniques. The two possible cases arising from oxygen interchange with atmosphere,
oxygen vacancies and interstitial cations, may be analyzed quantitatively
from the derived expressions. The possibility of another type of defects being
present in the samples, not associated to oxygen evolution, is not excluded.
Measurements were carried out in air and CO2 for different
Ti contents. The substitution tends to increase slightly the defect parameter
θ in YIG, while a CO2 reducing atmosphere is
much more effective than the Ti substitution for increasing θ. Calculations
for a given single-phased sample sintered in air show two possibilities: a
deficit of one oxygen atom for every 2.5 unit cells of 96 atoms, or one excess
cation for every 3.5 cells. Other samples show very similar results. The accuracy
involved in the measurements is about 2–3%. 相似文献
12.
13.
14.
Summary The generator contains diffusion tubes of known length and internal diameter. Once produced, the mixture of the carrier gas and acetone, the reference material, is sent through a chromatographic flame ionisation detector. Its signal reaches a constant level after a time corresponding to the stabilization time of the generator. The technique described is simple and gives repeatable results. 相似文献
15.
M.Victoria Mart?&#x;nez-D?&#x;azSagrario Esperanza Andrés de la EscosuraMarinella Catellani Sami YunusSilvia Luzzati Tomás Torres 《Tetrahedron letters》2003,44(46):8475-8478
Two new donor-acceptor copolymers comprising a polythiophene backbone, and bearing phthalocyanine chromophores on the side chains have been prepared. Preliminary photophysical characterization of these materials by FTIR photoinduced absorption indicates that electron transfer from the polythiophene to the phthalocyanine units takes place. 相似文献
16.
Martinez Alvarez R Herrera Fernandez A Chioua M Ramiro Perez P Villalba Vilchez N Guzman Torres F 《Rapid communications in mass spectrometry : RCM》1999,13(24):2480-2488
Several 5,6-dialkyl-2,4-diarylpyrimidines were prepared and their electron ionization (EI) mass spectra reported. The benzylic cleavage takes place easily together with an important McLafferty rearrangement. The involvement of the nitrogen atom appears to be important in the fragmentation of 5-methyl-substituted pyrimidines. In contrast, the 6-methyl-substituted pyrimidines undergo benzylic cleavage without hydrogen transfer. Thus, the difference in the mass spectrometric behaviour allows the identification of these isomeric compounds which, in contrast, exhibit only small differences in their NMR spectra. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
17.
Picquart M. López T. Gómez R. Torres E. Moreno A. Garcia J. 《Journal of Thermal Analysis and Calorimetry》2004,76(3):755-761
Sol-gel zirconia was characterized using high-resolution thermogravimetry (Hi-Res TG) and differential scanning calorimetry
(DSC) and compared with X-ray diffraction, Raman scattering, and UV-Vis spectroscopy. ZrO2-x(OH)2x·yH2O annealed below 400°C show typical behavior of amorphous material. As the annealing temperature is increased, the tetragonal
and monoclinic phases crystallize. Typical Hi-Res TG curve shows that the samples are continuously dehydrated in a long temperature
range, between room temperature and 600°C. The total mass loss relative to the initial mass is of about 29%. The DSC analysis
coupled with TG and structural information, indicate that the exothermic processes about 355 and 447°C can be related to the
nucleation process of the formation of tetragonal zirconia, with bulk crystallization at 447°C.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
18.
Low-temperature photolysis of benzoylphenyldiazomethane, 1, and diazoanthrone, 2, in the polycrystal phase resulted in the high-intensity ESR spectra of benxoylphenymethylene 1a and anthronylidene 2a, respectively. Photolyses of argon matrix-isolated 1 and 2, coupled with IR spectroscopy, have now been carried out. Photolysis of 1 yielded the IR spectrum of diphenylketene as the only IR-observable product and indicated the presence in the matrix of the
two s-E, s-Z, isomers of 1. On the other hand, photolysis of 2 yielded the IR spectrum of carbene 2a as the only observable product. 相似文献
19.
The fact that bitumens behave as non-Newtonian fluids results in non-linear relationships between their near-infrared (NIR) spectra and the physico-chemical properties that define their consistency (viz. penetration and viscosity). Determining such properties using linear calibration techniques [e.g. partial least-squares regression (PLSR)] entails the previous transformation of the original variables by use of non-linear functions and employing the transformed variables to construct the models. Other properties of bitumens such as density and composition exhibit linear relationships with their NIR spectra. Artificial neural networks (ANNs) enable modelling of systems with a non-linear property-spectrum relationship; also, they allow one to determine several properties of a sample with a single model, so they are effective alternatives to linear calibration methods. In this work, the ability of ANNs simultaneously to determine both linear and non-linear parameters for bitumens without the need previously to transform the original variables was assessed. Based on the results, ANNs allow the simultaneous determination of several linear and non-linear physical properties typical of bitumens. 相似文献
20.
3-Methoxy[2, 1]benzisoxazole-4, 7-quinones 1 and naphth[2,3-c]isoxazole-4,9-quinone 4 react with dimethyl sulfoxides to give sulfoximidoquinones 2 and 5 , sulfimidoquinones 8 and 11 respectively as major products. 相似文献