全文获取类型
收费全文 | 723667篇 |
免费 | 6333篇 |
国内免费 | 2065篇 |
专业分类
化学 | 365533篇 |
晶体学 | 10678篇 |
力学 | 36166篇 |
综合类 | 20篇 |
数学 | 96431篇 |
物理学 | 223237篇 |
出版年
2021年 | 6533篇 |
2020年 | 7009篇 |
2019年 | 7914篇 |
2018年 | 10610篇 |
2017年 | 10876篇 |
2016年 | 15141篇 |
2015年 | 8545篇 |
2014年 | 14184篇 |
2013年 | 33118篇 |
2012年 | 25483篇 |
2011年 | 30464篇 |
2010年 | 22594篇 |
2009年 | 22538篇 |
2008年 | 28418篇 |
2007年 | 28107篇 |
2006年 | 25761篇 |
2005年 | 22948篇 |
2004年 | 21302篇 |
2003年 | 19109篇 |
2002年 | 18979篇 |
2001年 | 20984篇 |
2000年 | 16022篇 |
1999年 | 12482篇 |
1998年 | 10637篇 |
1997年 | 10404篇 |
1996年 | 9745篇 |
1995年 | 8708篇 |
1994年 | 8656篇 |
1993年 | 8346篇 |
1992年 | 8956篇 |
1991年 | 9504篇 |
1990年 | 9066篇 |
1989年 | 8935篇 |
1988年 | 8553篇 |
1987年 | 8510篇 |
1986年 | 8118篇 |
1985年 | 10365篇 |
1984年 | 10784篇 |
1983年 | 9021篇 |
1982年 | 9310篇 |
1981年 | 8734篇 |
1980年 | 8425篇 |
1979年 | 9038篇 |
1978年 | 9276篇 |
1977年 | 9115篇 |
1976年 | 9041篇 |
1975年 | 8675篇 |
1974年 | 8511篇 |
1973年 | 8808篇 |
1972年 | 6321篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
We establish soliton-like asymptotics for finite energy solutions to the Schrödinger equation coupled to a nonrelativistic classical particle. Any solution with initial state close to the solitary manifold converges to a sum of a travelling wave and an outgoing free wave. The convergence holds in global energy norm. The proof uses spectral theory and the symplectic projection onto the solitary manifold in the Hilbert phase space. 相似文献
103.
We demonstrate a method that permits to obtain generalized solutions for some quasilinear equations and systems of hyperbolic
type. The corresponding variational principle is constructed using the theory of equilibrium of a potential in an external
field.
Dedicated to the memory of B. M. Levitan
Supported by RFBR grants Nos. 05-01-00522 and NSh-1551.2003.1, by Program No. 1 of the Branch of Mathematics, Russian Academy
of Sciences, and by INTAS project No. 03-51-6637. 相似文献
104.
The tape stripping technique is an experimental method frequently used for reconstruction of the in-depth distribution of various topically administered substances within the horny layer of human skin, e.g., compounds contained in sunscreens. Titanium dioxide (TiO2) nanoparticles (25–200 nm in diameter) are one such compound. Optical techniques which apply blue light are found to be suitable for reconstruction. However, the presence of particles affects the light propagation within the skin and therefore causes incorrect determination of strip thickness, leading to an improper reconstructed distribution of nanoparticle concentration revealed from the experimental data. This study evaluates the errors emerging from the use of blue (400 nm) and NIR (800 nm) radiation and finds the use of longer wavelength light more advantageous. Particles of different diameters are considered, and it is revealed that the application of small particles (25–60 nm) results in the lowest rate of error. 相似文献
105.
106.
107.
An algorithm is proposed which allows one to construct higher symmetries of arbitrary order for some special classes of hyperbolic
systems possessing integrals. The Pohlmeyer-Lund-Regge system and the open two-dimensional Toda lattices are shown to belong
to the class of systems where our algorithm is applicable.
__________
Translated from Fundamental’naya i Prikladnaya Matematika (Fundamental and Applied Mathematics), Vol. 10, No. 1, Geometry
of Integrable Models, 2004. 相似文献
108.
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
109.
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
110.
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