全文获取类型
收费全文 | 1399393篇 |
免费 | 25928篇 |
国内免费 | 7742篇 |
专业分类
化学 | 709659篇 |
晶体学 | 20319篇 |
力学 | 75363篇 |
综合类 | 110篇 |
数学 | 245219篇 |
物理学 | 382393篇 |
出版年
2021年 | 13584篇 |
2020年 | 16001篇 |
2019年 | 16136篇 |
2018年 | 12683篇 |
2016年 | 28152篇 |
2015年 | 20943篇 |
2014年 | 30671篇 |
2013年 | 74795篇 |
2012年 | 41172篇 |
2011年 | 39570篇 |
2010年 | 38051篇 |
2009年 | 39958篇 |
2008年 | 38218篇 |
2007年 | 34127篇 |
2006年 | 40378篇 |
2005年 | 32248篇 |
2004年 | 33071篇 |
2003年 | 30901篇 |
2002年 | 31852篇 |
2001年 | 32280篇 |
2000年 | 27179篇 |
1999年 | 23662篇 |
1998年 | 21534篇 |
1997年 | 21414篇 |
1996年 | 21368篇 |
1995年 | 19392篇 |
1994年 | 18859篇 |
1993年 | 18379篇 |
1992年 | 18921篇 |
1991年 | 19105篇 |
1990年 | 18334篇 |
1989年 | 18315篇 |
1988年 | 17959篇 |
1987年 | 17820篇 |
1986年 | 16785篇 |
1985年 | 23118篇 |
1984年 | 24221篇 |
1983年 | 20274篇 |
1982年 | 21907篇 |
1981年 | 21100篇 |
1980年 | 20427篇 |
1979年 | 20828篇 |
1978年 | 22002篇 |
1977年 | 21687篇 |
1976年 | 21399篇 |
1975年 | 20126篇 |
1974年 | 19809篇 |
1973年 | 20223篇 |
1972年 | 14700篇 |
1967年 | 12894篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
251.
252.
Non-stoichiometric ternary chalcogenides (Zn,Fe)S were prepared in the film form by pyrolytic spray deposition technique, using air/nitrogen as the carrier gas. The precursor solution comprised of ZnCl2, FeCl2 and thiourea. The depositions were carried out under optimum conditions of experimental parameters viz. carrier gas (air/nitrogen) flow rate, concentration of precursor constituents, nozzle substrate distance and temperature of quartz substrate. The deposited thin films were later sintered in argon at 1073 K for 120 min.The structural, compositional and optical properties of the sintered thin films were studied. X-ray diffraction studies of the thin films indicated the presence of (Zn,Fe)S solid solution with prominent cubic sphalerite phase while surface morphology as determined by scanning electron microscopy (SEM) revealed a granular structure.The chemical composition of the resulting thin films as analyzed by energy dispersive X-ray analysis (EDAX) reflected the composition of the precursor solutions from which the depositions were carried out with Fe at% values ranging from 0.4 up to 33.SEM micrographs of thin films reveal that the grain sizes of the thin films prepared using air as carrier gas and N2 as carrier gas are in the vicinity of 300 and 150 nm, respectively.The diffuse transmittance measurements for thin films, as a function of wavelength reveal the dependence of direct optical band gap on Fe content and type of phase. 相似文献
253.
The spatial structure of Bragg angles and the transfer functions of an acousto-optic cell are calculated for the cases of isotropic and anisotropic light diffraction in a uniaxial crystal. Their change with ultrasound frequency is traced. The possibility of image processing by acousto-optic filtration of the spatial spectrum of an image is considered. The results of experimental visualization of the transfer functions of a calcium molybdate crystal cell are presented. 相似文献
254.
Evaluation of the Planck-mean absorption coefficients from HITRAN and HITEMP databases 总被引:1,自引:0,他引:1
Hongmei ZhangMichael F. Modest 《Journal of Quantitative Spectroscopy & Radiative Transfer》2002,73(6):649-653
New values of Planck-mean absorption coefficients are presented for various gases, based on line-by-line calculations from the high-resolution databases, HITRAN and HITEMP. The new values are compared with previously published Planck-mean absorption coefficients. 相似文献
255.
V. Yu. Belashov 《Radiophysics and Quantum Electronics》2002,45(5):376-380
We consider generalizations of the earlier results, obtained for one-dimensional equations of the Kadomtsev–Petviashvili (KP) class, to two- and three-dimensional KP-class equations with an arbitrary nonlinearity index with allowance for the higher-order dispersion correction and terms describing dissipation and instability. The asymptotics of soliton and nonsoliton solutions are derived. Constructing phase portraits in the 8-dimensional space based on the results of a qualitative analysis of generalized Korteweg–de Vries (KdV) equations is discussed. 相似文献
256.
H.S RagabA Shehap M.S Abo EllilW.H Osman F.H Abd El-Kader 《Journal of Physics and Chemistry of Solids》2002,63(10):1839-1847
Ternary-phase ceramic system of Li2O Al2O3 4SiO2 doped with CuO, FeO and TiO2 has been prepared and subjected to dc electrical conductivity and thermally stimulated depolarization current (TSDC) measurements as a function of temperature (30-250 °C) and field strength. The electrical conductivity results are explained by assuming both ionic and electronic conduction mechanisms coexist with different contributions over the whole temperature range of experiments. TSDC spectra have been found to be characterized by a broad intense relaxation peak, which can be attributed to an ionic charge polarization. The broad relaxation transitions are apparently a result of the nonuniform nature of this process. Activation energies are calculated for both dc electrical conductivity and TSDC according to Arrhenius equation and initial rise method, respectively. 相似文献
257.
The sound field in the region of a deep shadow behind an impedance cylinder is analyzed for the case of plane wave diffraction by the cylinder surface. The main part of the field is represented by a cylindrical wave that has a complex index determined from the boundary conditions and decays with the angular coordinate. An expression for the amplitude of this wave is determined by extracting it from the total field formed in the shadow region. It is demonstrated that this wave approximates more closely the total field behind the cylinder, as compared to the least damped wave in the field representation obtained on the basis of the Watson transform. A way to improve the sound barriers is indicated. 相似文献
258.
A two-dimensional, nonlinear, compressible, diabatic, nonhydrostatic photochemical-dynamical gravity wave model has been advanced. The model includes diabetic process produced by photochemistry and the effect of gravity wave on atmospheric chemical species. In the horizontal direction, the pseudospectral method is used. The finite difference approximations are used in vertical direction z and time t. The FICE method is used to solve the model. The model results on small amplitude fluctuation are very close to those of linear theory, which demonstrates the correctness of the model.
相似文献259.
We consider the problem of maximizing a linear fractional function on the Pareto efficient frontier of two other linear fractional functions. We present a finite pivoting-type algorithm that solves the maximization problem while computing simultaneously the efficient frontier. Application to multistage efficiency analysis is discussed. An example demonstrating the computational procedure is included. 相似文献
260.
A noiselike fine structure of ferromagnetic resonance spectra in magnetic powders was investigated after ultrasonic treatment. Magnetic interactions between particles are proved to have an influence upon the fine structure formation. After decreasing dipole-dipole magnetic interactions in dilute suspension a special order appears in fine-structure spectra, which is generally the same for different systems. 相似文献