全文获取类型
收费全文 | 1468篇 |
免费 | 28篇 |
国内免费 | 1篇 |
专业分类
化学 | 798篇 |
晶体学 | 25篇 |
力学 | 28篇 |
综合类 | 2篇 |
数学 | 209篇 |
物理学 | 435篇 |
出版年
2022年 | 5篇 |
2021年 | 11篇 |
2020年 | 11篇 |
2019年 | 20篇 |
2018年 | 47篇 |
2017年 | 32篇 |
2016年 | 70篇 |
2015年 | 51篇 |
2014年 | 60篇 |
2013年 | 140篇 |
2012年 | 47篇 |
2011年 | 84篇 |
2010年 | 52篇 |
2009年 | 50篇 |
2008年 | 68篇 |
2007年 | 54篇 |
2006年 | 46篇 |
2005年 | 49篇 |
2004年 | 62篇 |
2003年 | 57篇 |
2002年 | 33篇 |
2001年 | 51篇 |
2000年 | 28篇 |
1999年 | 30篇 |
1998年 | 23篇 |
1997年 | 20篇 |
1996年 | 13篇 |
1995年 | 16篇 |
1994年 | 10篇 |
1993年 | 21篇 |
1992年 | 13篇 |
1991年 | 13篇 |
1990年 | 12篇 |
1989年 | 11篇 |
1988年 | 8篇 |
1987年 | 19篇 |
1986年 | 11篇 |
1985年 | 12篇 |
1984年 | 15篇 |
1983年 | 5篇 |
1982年 | 11篇 |
1981年 | 14篇 |
1980年 | 13篇 |
1979年 | 9篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1975年 | 6篇 |
1973年 | 5篇 |
1929年 | 5篇 |
1927年 | 5篇 |
排序方式: 共有1497条查询结果,搜索用时 328 毫秒
91.
Łukasz Wiśniewski Katarína Vaňková Pavel Ačai Milan Polakovič 《Chemical Papers》2014,68(12):1649-1655
Galacto-oligosaccharides are typically produced by an enzymatic reaction when the post-reaction mixture contains considerable amounts of lactose and glucose and a smaller amount of galactose. In order to develop a process of chromatographic removal of saccharide impurities, adsorption equilibria and kinetics of these di- and monosaccharides were investigated for Diaion UBK 530, an industrialgrade strong cation-exchanger in the Na+ form. Frontal chromatographic experiments were carried out in the temperature range of 30–70°C and a broad interval of saccharide concentrations up to 350 g L?1. Breakthrough curves were described using the equilibrium-dispersive model with the linear adsorption isotherm. Both the distribution and the axial dispersion coefficient values depended on the saccharide molecule type and size. No significant effect of temperature or concentration on the distribution coefficient was observed. The apparent dispersion coefficients of all saccharides exhibited some decrease with the temperature, which was caused by the decrease of the intraparticle mass transfer resistance. An analysis showed that both the intraparticle mass transfer and the axial dispersion had a significant influence on the front dispersion. 相似文献
92.
Denis Mashkovtsev Wataru Mizukami Jacek Korchowiec Anna Stachowicz-Kuśnierz Yuriko Aoki 《Journal of computational chemistry》2020,41(25):2203-2212
The elongation method with intermediate mechanical and electrostatic embedding (ELG-IMEE) is proposed. The electrostatic embedding uses atomic charges generated by a charge sensitivity analysis (CSA) method and parameterized for three different population analyses, namely, the Merz–Singh–Kollman scheme, the charge model 5, and the atomic polar tensor. The obtained CSA models were tested on two model systems. Test calculations show that the electrostatic embedding provides several times of decrease in the difference of energies of testing and reference calculations in comparison with the conventional elongation approach (ELG). The mechanical embedding is implemented in a combination of the conventional elongation method and the ONIOM approach. Moreover, it was demonstrated that the geometry optimization with the ELG-IMEE reduces the errors in the optimized structures by about one order in root-mean-square deviation, when compared to ELG. 相似文献
93.
The paper presents a study of the effect of a constant magnetic field (CMF) on the basic processes of quercetin electrochemical reactions. According to the observation made in previous studies, the presence of a double bond in the C-ring of quercetin enhances the antioxidant properties of that compound, whereas the presence of −OH groups also affects the antioxidant properties. Using cyclic voltammetry it was found that the constant magnetic field improves the efficiency of quercetin electrooxidation, especially of the third stage of the process, i. e. the stage in which the oxidation of the OH groups in the A-ring is the most difficult. The use of HPLC confirmed the electrochemical measurements and the results of cyclic voltammetry studies. The beneficial effect of the magnetic field on the efficiency of quercetin oxidation was confirmed by the results of impedance spectroscopy measurements. 相似文献
94.
The development of technology of new semiconductor devices requires fundamental studies of a number of phenomena taking place in semiconductors during the doping process or accompanying the doping process. These studies are concerned with the following problems: 1. Diffusion of gold in silicon and the effect of diffusion layers (particularly phosphorus layers) and epitaxial silicon layers on the distribution of gold in thin silicon plates. 2. Distribution of admixtures in silicon introduced with the aid of the ion implantation technique. Our studies concerned with the second of the above mentioned problems comprised an autoradiographic examination of the homogeneity of the beam of phosphorus ions implanted in silicon, and a study of some apparatus factors and of the purity of the basic material on the implantation. 相似文献
95.
96.
D. Kamińska A. Gajos E. Czerwiński D. Alfs T. Bednarski P. Białas C. Curceanu K. Dulski B. Głowacz N. Gupta-Sharma M. Gorgol B. C. Hiesmayr B. Jasińska G. Korcyl P. Kowalski W. Krzemień N. Krawczyk E. Kubicz M. Mohammed Sz. Niedźwiecki M. Pawlik-Niedźwiecka L. Raczyński Z. Rudy M. Silarski A. Wieczorek W. Wiślicki B. Zgardzińska M. Zieliński P. Moskal 《The European Physical Journal C - Particles and Fields》2016,76(8):445
97.
R. Kruszka M. Ekielski K. Gołaszewska K. Korwin-Mikke Z. Sidor M. Wzorek D. Pierścińska R. Sarzała T. Czyszanowski A. Piotrowska 《Opto-Electronics Review》2011,19(1):51-55
The results of modelling of the influence of photonic crystal on the performance of VCSEL-type semiconductor laser structure
are shown and indicate that the use of those structures would significantly improve the working parameters of the devices.
The method of fabrication of photonic crystals in the Bragg mirrors of GaAs/AlGaAs-based VCSELs is presented. 相似文献
98.
Michał Rachwalski Stanisław Leśniak Piotr Kiełbasiński 《Tetrahedron: Asymmetry》2010,21(21-22):2687-2689
Diastereomerically pure tridentate heteroorganic ligands containing hydroxyl, sulfinyl and aziridine moieties as nucleophilic centers, capable of binding to various organometallic reagents, have been proven to be highly efficient catalysts in the enantioselective addition of phenylethynylzinc to aldehydes to give the desired products in very high yields (up to 95%) and with ee’s up to 90%. The influence of the stereogenic centers located on the sulfinyl sulfur atom and in the aziridine moiety on the stereochemical course of the reaction is also discussed. 相似文献
99.
P. T. Jochym K. Parlinski A. M. Oleś 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(2):173-179
The magnetization distribution, its energetic characterization by the
interlayer coupling constants and lattice dynamics of (001)-oriented
Fe/Pt multilayers are investigated using density functional theory
combined with the direct method to determine phonon frequencies.
It is found that ferromagnetic order between consecutive Fe layers is
favoured, with the enhanced magnetic moments at the
interface. The bilinear and biquadratic coupling coefficients between Fe
layers are shown to saturate fast with increasing thickness of
nonmagnetic Pt layers which separate them. The phonon calculations
demonstrate a rather strong dependence of partial iron phonon
densities of states on the actual position of Fe monolayer
in the multilayer structure. 相似文献
100.
J. Gaca M. Wójcik A. Jasik K. Pierściński M. Kosmala A. Turos A. M. Abdul-Kaderd 《Opto-Electronics Review》2008,16(1):12-17
GaAs/AlAs Bragg mirrors on GaAs with varied number of layer pairs were grown, by molecular beam epitaxy (MBE), to be applied
for semiconductor saturable absorber mirrors (SESAMs) and intensity modulators. Due to the random variation of the growth
rate, substrate surface roughness, and interdiffusion at the interfaces, precise control of the growth conditions of deposited
layers poses a serious problem. Usually, thickness variations and composition grading at the heterointefaces result in variations
of the mirror reflectivity. In this paper, the high resolution X-ray diffraction (HRXRD), optical reflectance, Rutherford
backscattering/channelling (RBS), supported by numerical evaluation methods were employed to determine both the exact thickness
of each layer and the composition grading at the interface between succeeding layers of GaAs/AlAs-based mirrors. To reduce
ambiguity and to speed up the analysis, the rocking curves and RBS spectra were simulated concurrently, using results of one
simulation to verify the others. This process was carried out until the best fit between experimental and calculated curves
was achieved. The complementary use of both methods results in improved sensitivity and makes the whole process of evaluation
of the thickness variation of each layer and the size of the composition grading at the interfaces less time consuming. 相似文献