全文获取类型
收费全文 | 863篇 |
免费 | 36篇 |
国内免费 | 3篇 |
专业分类
化学 | 556篇 |
晶体学 | 22篇 |
力学 | 6篇 |
数学 | 29篇 |
物理学 | 289篇 |
出版年
2022年 | 8篇 |
2021年 | 17篇 |
2020年 | 20篇 |
2019年 | 13篇 |
2018年 | 19篇 |
2017年 | 14篇 |
2016年 | 34篇 |
2015年 | 22篇 |
2014年 | 21篇 |
2013年 | 87篇 |
2012年 | 69篇 |
2011年 | 53篇 |
2010年 | 41篇 |
2009年 | 38篇 |
2008年 | 43篇 |
2007年 | 46篇 |
2006年 | 36篇 |
2005年 | 26篇 |
2004年 | 23篇 |
2003年 | 16篇 |
2002年 | 24篇 |
2001年 | 8篇 |
2000年 | 11篇 |
1999年 | 7篇 |
1998年 | 6篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 14篇 |
1994年 | 11篇 |
1993年 | 8篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 7篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1985年 | 4篇 |
1984年 | 7篇 |
1983年 | 11篇 |
1982年 | 5篇 |
1981年 | 8篇 |
1980年 | 12篇 |
1979年 | 4篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1973年 | 7篇 |
1970年 | 9篇 |
1963年 | 3篇 |
1957年 | 3篇 |
排序方式: 共有902条查询结果,搜索用时 218 毫秒
121.
The solubility of hydrous UO2 in sodium hydroxide solutions containing sodium dithionite and/or Zn metal powder as reductants has been measured. The results provide no firm evidence for any amphoteric behavior of U(IV) but do set an upper limit of K ≤ 2 x 10?23 for the hypothetical reaction: The results provide no evidence for such a reaction. 相似文献
122.
Total cross-section for electron impact excitation of the resonance levels in Li, Na and K are calculated using the method
due to Crothers and McCarroll. The results are compared with other available theoretical and experimental data. 相似文献
123.
In the present paper, the general expressions for temperature distribution in an orthotropic plate of finite dimensions have been derived under the influence of an arbitrary volume heat source and arbitrary initial temperature distribution. The boundary conditions prescribed on the faces are of second kind. The solution is obtained by constructing an eigen value problem. The expression for unsteady temperature distribution consists of two parts—steady and pseudo-steady. The pseudo-steady parts of the solution have been obtained with the help of finite integral transform technique. The general expressions are further studied under different cases. The whole analysis is presented in the dimensionless form with the help of various dimensionless parameters,viz., F o , P o , K i , etc. 相似文献
124.
A magnetic domain wall (DW) injected and pinned at a notch in a permalloy nanowire is shown to exhibit four well-defined magnetic states, vortex and transverse, each with two chiralities. These states, imaged using magnetic force microscopy, are readily detected from their different resistance values arising from the anisotropic magnetoresistance effect. Whereas distinct depinning fields and critical depinning currents in the presence of magnetic fields are found, the critical depinning currents are surprisingly similar for all four DW states in low magnetic fields. We observe current-induced transformations between these DW states below the critical depinning current which may account for the similar depinning currents. 相似文献
125.
Rai-Constapel V Liebermann HP Buenker RJ Rai SN 《The journal of physical chemistry. A》2006,110(2):404-411
Potential energy curves and properties of the low-lying electronic states of tellurium oxide have been computed using a configuration interaction treatment that includes the spin-orbit coupling interaction. Relativistic effective core potentials (RECPs) are used to describe the inner shells of both the Te and O atoms. Good agreement is obtained for the spectroscopic constants of the X1-X2(3)sigma-, a1delta, and b1sigma+ states for which experimental data are available. The ratio of the parallel and perpendicular b-X transition moments, as well as the radiative lifetime of the b state, was computed, and both results were also found to be in good agreement with measurement. The energetic order of the electronic states in TeO appears to be very similar to that observed for the isovalent O2 molecule, but the Rydberg valence-mixing effects that are so prominent in the latter's spectrum (e.g., for the Schumann-Runge bands) are totally absent in TeO. 相似文献
126.
The absorption and the fluorescence spectra of Pr3+ ion doped in aluminum, barium, calcium fluoride (ABCF) glass have been studied. Judd-Ofelt theory has been used to derive the optical parameters, viz. the oscillator strength, transition probability, branching ratio, stimulated emission cross section, etc. A broadband upconversion has been observed at different wavelengths throughout the visible region when pumped with 810 nm radiation from a Ti-sapphire laser. 相似文献
127.
S. K. Singh A. K. Singh D. Kumar O. Prakash S. B. Rai 《Applied physics. B, Lasers and optics》2010,98(1):173-179
A nano-crystalline La2O3: Er3+/Yb3+ phosphor sample has been synthesized through the solution combustion route using urea as a reducing agent. Thermal, structural
and optical characterizations have been carried out to explore several of its properties. By thermal analysis one concludes
to the presence of moisture and hydroxide phases [La(OH)3 and LaOOH] of lanthanum in the as-synthesized sample, which further changes to La2O3 phase above 600°C temperature. Up-conversion (UC) study shows the intense emission bands in the UV, blue, green and red regions.
This paper also reports the first observation of UC emission bands extending up to the UV (240 nm) region on excitation with
976 nm wavelength. Heat treatment of the samples shows a change in the crystallite phase along with crystallite growth and
relative UC luminescence intensities. The input pump power dependence shows the involvement of up to four photons. 相似文献
128.
Vijay Singh Vineet Kumar Rai S. Watanabe T. K. Gundu?Rao Isabelle Ledoux-Rak Ho-Young Kwak 《Applied Physics A: Materials Science & Processing》2010,100(4):1123-1130
YAG phosphor powders doped/codoped with Er3+/(Er3+ + Yb3+) have been synthesised by using the solution combustion method. The effect of direct pumping into the 4I11/2 level under 980 nm excitation of doped/codoped Er3+/Yb3+−Er3+ in Y3Al5O12 (YAG) phosphor responsible for an infrared (IR) emission peaking at ∼1.53 μm corresponding to the 4I13/2→4I15/2 transition has been studied. YAG exhibits three thermally-stimulated luminescence (TSL) peaks at around 140°C, 210°C and
445°C. Electron spin resonance (ESR) studies were carried out to identify the centres responsible for the TSL peaks. The room
temperature ESR spectrum of irradiated phosphor appears to be a superposition of two distinct centres. One of the centres
(centre I) with principal g-value 2.0176 is identified as O− ion, while centre II with an isotropic g-factor 2.0020 is assigned to an F+ centre (singly ionised oxygen vacancy). An additional defect centre is observed during thermal-annealing experiments and
this centre (assigned to F+ centre) seems to originate from an F-centre (oxygen vacancy with two electrons) and these two centres appear to correlate
with the observed high-temperature TSL peak in YAG phosphor. 相似文献
129.
A higher order uniformly convergent method for singularly perturbed parabolic turning point problems
Swati Yadav Pratima Rai Kapil K. Sharma 《Numerical Methods for Partial Differential Equations》2020,36(2):342-368
In this article, we study numerical approximation for a class of singularly perturbed parabolic (SPP) convection-diffusion turning point problems. The considered SPP problem exhibits a parabolic boundary layer in the neighborhood of one of the sides of the domain. Some a priori bounds are given on the exact solution and its derivatives, which are necessary for the error analysis. A numerical scheme comprising of implicit finite difference method for time discretization on a uniform mesh and a hybrid scheme for spatial discretization on a generalized Shishkin mesh is proposed. Then Richardson extrapolation method is applied to increase the order of convergence in time direction. The resulting scheme has second-order convergence up to a logarithmic factor in space and second-order convergence in time. Numerical experiments are conducted to demonstrate the theoretical results and the comparative study is done with the existing schemes in literature to show better accuracy of the proposed schemes. 相似文献
130.
R.N. Rai R.S.B. Reddi U.S. Rai 《Progress in Crystal Growth and Characterization of Materials》2013,59(2):73-111
The aim of this review is to emphasize solvent free or green synthesis, a most efficient utilization of starting materials to give maximum yield, and an alternative route to producing novel promising materials. In this regard the phase diagram study has shown applications in the determination of the precise composition of binary compounds of a specific nature and in the identification of the parameters that affect the crystal growth. To provide an overview worthy of phase diagram, physicochemical, thermal and structure investigations; studies of eleven systems, namely, urea–m-nitrobenzoic acid, urea–p-nitrophenol, urea–resorcinol, benzoin–o-phenylenediamine, pyrene–m-dinitrobenzene, vanillin–p-anisidine, resorcinol–p-dimethylaminobenzaldehyde, benzophenone–diphenylamine, anthracene–picric acid, 8-hydroxyquinoline–salicylic acid and 8-hydroxyqunoline–1,2,3-trihydroxybenzene forming organic complexes, have been reported. In addition, the original data of a newly synthesized complex of m-hydroxybenzaldehyde (HB) and p-chloroaniline (CA) is being reported for the first time. The phase diagram of HB–CA system also shows the formation of a complex in 1:1 M ratio, and two eutectics on either side of the complex. The complex's formation was studied using FTIR, NMR, DSC and powder X-ray diffraction techniques. The thermodynamic parameters such as heat of mixing, entropy of fusion, roughness parameter, interfacial energy and excess thermodynamic functions were calculated using the heat of fusion values. The single crystal growth and the atomic packing studies of some of the complexes have confirmed the formation of complexes. The optical transmittance efficiency and transparency of novel HB–CA complex crystal were found to be 70% and 399 nm, respectively. 相似文献