全文获取类型
收费全文 | 704篇 |
免费 | 22篇 |
国内免费 | 1篇 |
专业分类
化学 | 346篇 |
晶体学 | 13篇 |
力学 | 24篇 |
数学 | 80篇 |
物理学 | 264篇 |
出版年
2023年 | 4篇 |
2022年 | 10篇 |
2021年 | 14篇 |
2020年 | 13篇 |
2019年 | 19篇 |
2018年 | 23篇 |
2017年 | 22篇 |
2016年 | 34篇 |
2015年 | 20篇 |
2014年 | 41篇 |
2013年 | 51篇 |
2012年 | 54篇 |
2011年 | 64篇 |
2010年 | 25篇 |
2009年 | 34篇 |
2008年 | 32篇 |
2007年 | 19篇 |
2006年 | 14篇 |
2005年 | 15篇 |
2004年 | 7篇 |
2003年 | 15篇 |
2002年 | 16篇 |
2001年 | 5篇 |
2000年 | 6篇 |
1999年 | 9篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 8篇 |
1995年 | 6篇 |
1994年 | 13篇 |
1993年 | 7篇 |
1992年 | 6篇 |
1990年 | 9篇 |
1989年 | 7篇 |
1988年 | 13篇 |
1987年 | 9篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 8篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1955年 | 4篇 |
1954年 | 2篇 |
排序方式: 共有727条查询结果,搜索用时 109 毫秒
61.
The interfacial and thermodynamic properties of a non-ionic surfactant, poly[oxyethylene(10)] lauryl ether, [C12H25(OCH2CH2)10OH], in aqueous solution in the presence of amino acids have been investigated. Critical micelle concentrations (cmcs) were determined by surface tension measurements at different additive concentrations and temperatures using a du Nouy tensiometer. From the surface tension data, the surface excess concentration (F), the minimum area per molecule (Amin), and the surface pressure at the cmc(?cmc) were evaluated. Thermodynamic parameters of adsorption and micellization were evaluated and discussed. The other solution properties of this surfactant like the cloud point viscosity, and foaming have been determined in the presence of different concentrations of alanine and glycine. 相似文献
62.
A theoretical framework for treating the effects of magnetic fieldH on the pairing theory of superconductivity is considered, where the field is taken in an arbitrary direction with respect
to crystal axes. This is applicable to closed, as well as open normal state Fermi surface (FS), including simple layered metals.
The orbital effects of the magnetic field are treated semiclassically while retaining the full anisotropic paramagnetic contribution.
Explicit calculations are presented in the limits |H| → |H
c2(T)|,T ∼ 0 andT →T
c(|H|), |H| ∼ 0. Effects of weak nonmagnetic impurity scattering, without vertex corrections, have also been taken into account in a
phenomenological way. The final results for the case of open FS and layered materials are found to differ considerably from
those of the closed FS. For example, an important parameter,h(T=0)=|Hc2(0)|/[-Tδ|H
c2
T|δT]T{s0} for the case of a FS open ink
z-direction with thek
z-bandwidth, 4t
3, very small compared to the Fermi energy,E
F, is close to 0.5906, compared to 0.7273 for the closed FS, in the clean limit. Analytical results are given for the magnetic
field dependence ofT
c and the temperature dependence of H
c2 for a model of layered superconductors with widely open FS. For a set of band structure parameters for YBa2Cu3O7 used elsewhere, we find reasonable values for the upper critical fieldH
c2(0), the slope (dH
c2/dT)T
c0, anisotropic coherence lengths ζi(T=0),i=x, y, z, and (dT
c/d|H|)|H| → 0. 相似文献
63.
The phonon dispersion curves for aluminium arsenide and antimonide have been investigated by using a deformation bond approximation
model. The results obtained from this model are compared with the experimental values wherever it is available. Since there
is no complete experimental phonon dispersion curves for AlAs, we could not compare our calculated results, but the results
of AlSb have been compared with the inelastic neutron scattering measurements at 15 K. However, we compare the phonon frequencies
of AlAs and AlSb at critical points of the Brillouin zone obtained by our calculations and Raman spectroscopy measurements.
This model predicts the phonon modes satisfactorily in all the symmetry directions of the Brillouin zone (BZ). The spectrum
has similar features as observed in other III–V compound semiconductors. 相似文献
64.
B. K. Jha 《Heat and Mass Transfer》1997,33(3):261-263
An analytical study is made to examine the flow behaviour of a fully developed transient free-convective flow of an incompressible
viscous fluid between two heated vertical walls in a porous system. A Laplace transform technique has been employed to obtain
the expression for velocity, temperature and skin-friction. The influence of the various parameters, entering into the problem,
on the velocity field and skin-friction is discussed in detail.
Received on 11 March 1997 相似文献
65.
Lattice vibrational properties of uranium pnictides have been studied using breathing shell model (BSM) which includes breathing
motion of electrons of the U-atoms due tof−d hybridization. The phonon dispersion curves of U-pnicitides calculated from the present model agree reasonably well with
the measured data. A comparison has been made between BSM and our results reported earlier obtained from three-body force
rigid ion model to reveal the importance of the short-range electron-phonon interactions in these compounds. We also report,
for the first time, the two phonon density of states and specific heat for these compounds. 相似文献
66.
67.
Basant Kumar Jha 《Heat and Mass Transfer》2005,41(8):675-679
This study addresses the Brinkman-extended Darcy model (Brinkman flow) of a laminar free-convective flow in an annular porous region. Closed form expressions for Velocity field, Temperature field, Skin-friction and Mass flow rate are given, under a thermal boundary condition of mixed kind at the outer surface of the inner cylinder while the inner surface of the outer cylinder is isothermal. The governing independent parameters are identified to be Darcy number (Da) and ratio of outer to inner radii (R). It is hoped that the study of such flows gives limiting conditions for developing flows and provides an analytical check on numerical solutions for more complex problems dealing with non-Darcian free-convection flow in an annular region. 相似文献
68.
A simple and efficient procedure has been developed for the synthesis of substituted pyrrole-fused isocoumarins from easily available ninhydrin. The cyclic hemiaminal dihydroxy-indenopyrroles, the adducts of ninhydrin with enamines of acetylacetone, give pyrrole-fused isocoumarins upon heating in acidic medium. The process constitutes an interesting acid-catalyzed rearrangement to eight-membered lactams followed by intramolecular cyclization involving the amino and keto groups. 相似文献
69.
N. Kumar S. K. Jha S. S. Chaturvedi 《Journal of Radioanalytical and Nuclear Chemistry》2011,290(3):525-533
Radiation dose-risk assessment was carried out for cereal species Brassica compestris var. dichotoma, Oryza sativa var. Shalum1, Zea mays, Lactuca indica, Cumunis sativum, and Clocasia esculanta due to naturally available radionuclides 40K, 238U and 232Th in Domiasiat area. The activity in biota and corresponding soil was measured by precipitation method using NaI(TI) detector.
Transfer factor (TF) was for Oryza spp. (1.00E−01-40K, 8.76E−05-232Th, and 9.11E−05-238U), for Brassica spp. (5.39E−01-40K, 8.17E−04-232Th and 2.96E−04-238U) and for Zea spp. (3.41E−01-40K, 5.84E−05-232Th, 8.87E−05-238U) etc., respectively. A detailed physio-morphological study of the biota and extensive investigation of ecosystem was carried
out for assessment. The data was modeled using FASSET for dose estimation and obtained total dose was 1.58E−04
\upmu Gy h-1 \upmu \hbox{Gy}\,h^{-1} in Oryza spp., 2.87E−04
\upmu Gy h-1 \upmu \hbox{Gy}\,h^{-1}
Brassica spp. and 6.90E−03
\upmu Gy h-1 \upmu \hbox{Gy}\,h^{-1} in Zea spp. etc. The dose was compared with the UNSCEAR dataset for screening level dose for biota. Zea spp. was more susceptible for the chronic radiation exposure. 相似文献
70.
It is well‐established that exposure of aqueous suspensions of titanium dioxide (TiO2) nanoparticles to ultraviolet A (UVA) light produces reactive oxygen species which leads to biological damage. However, there is disagreement in the literature as to the exact nature of these species and how they are formed. Using a number of different spin traps (i.e. PBN, POBN, DMPO, DEPMPO), we have shown that the primary damaging species produced on irradiation of an aqueous suspension of TiO2 is the hydroxyl radical, which is formed at the valence band hole under both aerobic and hypoxic conditions. Hydroxyl radical production is enhanced by the presence of oxygen which probably reacts with the conduction band electrons or resultant Ti3+, inhibiting hole‐electron recombination, although we find no evidence of reaction of oxygen to form free superoxide radical anions or of the formation of any other radical at that site. The present results suggest that the resulting O2 ?? species may not be as labile as previously thought and may possibly undergo further reduction to the O 2 2? dianion. Hydroxyl radicals formed at the surface of the TiO 2 readily react with substrates containing an abstractable hydrogen to produce secondary radicals that, in biological systems, could lead to cell damage. 相似文献