全文获取类型
收费全文 | 1726篇 |
免费 | 30篇 |
国内免费 | 98篇 |
专业分类
化学 | 483篇 |
晶体学 | 1篇 |
力学 | 8篇 |
数学 | 55篇 |
物理学 | 1307篇 |
出版年
2024年 | 1篇 |
2023年 | 49篇 |
2022年 | 13篇 |
2021年 | 10篇 |
2020年 | 34篇 |
2019年 | 40篇 |
2018年 | 57篇 |
2017年 | 37篇 |
2016年 | 39篇 |
2015年 | 41篇 |
2014年 | 61篇 |
2013年 | 92篇 |
2012年 | 109篇 |
2011年 | 154篇 |
2010年 | 95篇 |
2009年 | 101篇 |
2008年 | 126篇 |
2007年 | 101篇 |
2006年 | 101篇 |
2005年 | 59篇 |
2004年 | 51篇 |
2003年 | 56篇 |
2002年 | 63篇 |
2001年 | 45篇 |
2000年 | 65篇 |
1999年 | 52篇 |
1998年 | 42篇 |
1997年 | 17篇 |
1996年 | 15篇 |
1995年 | 15篇 |
1994年 | 19篇 |
1993年 | 11篇 |
1992年 | 8篇 |
1991年 | 8篇 |
1990年 | 7篇 |
1989年 | 13篇 |
1988年 | 7篇 |
1987年 | 8篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1981年 | 4篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有1854条查询结果,搜索用时 15 毫秒
41.
We consider the superpositions of spin coherent states and study the coherence properties and spin squeezing in these states. The spin squeezing is examined using a new version of spectroscopic squeezing criteria. The results show that the antibuching effect can be enhanced and spin squeezing can be generated in the superpositions of two spin coherent states. 相似文献
42.
M. D. Martín L. Via J. K. Son R. Ruf E. E. Mendez 《Physica E: Low-dimensional Systems and Nanostructures》2000,6(1-4)
We have used time-resolved photoluminescence spectroscopy to study the light emission dynamics in a semiconductor microcavity as a function of excitation density and exciton-cavity detuning. We paid special attention to polariton spin relaxation by using circularly polarized excitation. We have found a striking behavior of the photoluminescence degree of polarization, which reaches its maximum value at a finite time. As the excitation density is increased and the system enters the stimulated emission regime, this maximum is followed by a negative dip, whose depth strongly depends on exciton-cavity detuning. 相似文献
43.
E. García-Matres J.L Martínez J. Rodríguez-Carvajal 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(1):59-70
A neutron diffraction study, as a function of temperature, of the title compounds is presented. The whole family (space group
Immm, a
≈ 3.8?, b
≈ 5.8?, c
≈ 11.3?) is structurally characterised by the presence of flattened NiO6 octahedra that form chains along the a-axis, giving rise to a strong Ni-O-Ni antiferromagnetic interaction. Whereas for Y-compound only strong 1D correlations exist
above 1.5 K, presenting the Haldane gap characteristic of 1D AF chain with integer spin, 3D AF ordering is established simultaneously
for both R and Ni sublattices at temperatures depending on the rare earth size and magnetic moment. The magnetic structures
of R2BaNiO5 ( R
=
Nd, Tb, Dy, Ho, Er and Tm) have been determined and refined as a function of temperature. The whole family orders with a magnetic
structure characterised by the temperature-independent propagation vector
= (1/2, 0, 1/2). At 1.5 K the directions of the magnetic moments differ because of the different anisotropy of the rare earth ions. Except
for Tm and Yb (which does not order above 1.5 K), the magnetic moment of the R3+ cations are close to the free-ion value. The magnetic moment of Ni2+ is around 1.4
, the strong reduction with respect to the free-ion value is probably due to a combination of low-dimensional quantum effects
and covalency. The thermal evolution of the magnetic structures from T
N
down to 1.5 K is studied in detail. A smooth re-orientation, governed by the magnetic anisotropy of R3+, seems to occur below and very close to T
N
in some of these compounds: the Ni moment rotates from nearly parallel to the a-axis toward the c-axis following the R moments. We demonstrate that for setting up the 3D magnetic ordering the R-R exchange interactions cannot
be neglected.
Received 19 July 2001 相似文献
44.
We present a calculation of the electronic Raman cross section for the scattering of light across the energy gap of an antiferromagnetic insulator. The antiferromagnet is described in terms of a spin density wave state for the Hubbard model at half filling. We consider the coupling of the light to the current density and the inverse mass tensor on equal footing. A comparison of the cross section for different scattering geometries is given. 相似文献
45.
Philippe Bertani Jsus Raya Pierre Reinheimer Rgis Gougeon Luc Delmotte Jrme Hirschinger 《Solid state nuclear magnetic resonance》1999,13(4):255-229
19F/29Si Hartmann–Hahn continuous wave cross-polarization (CP) has been applied under fast magic-angle spinning (MAS) to a powder sample of octadecasil. Strong oscillations occur during CP on a sideband matching condition between the isolated 29Si–19F spin pairs formed by the silicons in the D4R units and the fluoride anions. The magnitude of the dipolar coupling constant was deduced directly from the line-splitting between the intense singularities of the Pake-like patterns obtained by Fourier transformation of the oscillatory polarization transfer. The corresponding Si–F internuclear distance, r=2.62±0.05 Å, is found to be in very good agreement with the X-ray crystal structure and the value of 2.69±0.04 Å recently reported from rotational echo double resonance (REDOR) and transferred echo double resonance (TEDOR) nuclear magnetic resonance (NMR) experiments. Furthermore, the CP technique is still reliable under fast MAS where both REDOR and TEDOR sequences suffer from severe artefacts due to finite pulse lengths. In octadecasil, a spinning frequency of 14 kHz is shown to be necessary for an effective suppression of 19F–19F spin diffusion. The influences of experimental missettings and radiofrequency (RF) field inhomogeneity are taken into account. 相似文献
46.
P. Fröbrich P.J. Jensen P.J. Kuntz A. Ecker 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(4):579-594
The field-induced reorientation of the magnetization of ferromagnetic films is treated within the framework of many-body Green's
function theory by considering all components of the magnetization. We present a new method for the calculation of expectation
values in terms of the eigenvalues and eigenvectors of the equations of motion matrix for the set of Green's functions. This
formulation allows a straightforward extension of the monolayer case to thin films with many layers and for arbitrary spin
and moreover provides a practicable procedure for numerical computation. The model Hamiltonian includes a Heisenberg term,
an external magnetic field, a second-order uniaxial single-ion anisotropy, and the magnetic dipole-dipole coupling. We utilize
the Tyablikov (RPA) decoupling for the exchange interaction terms and the Anderson-Callen decoupling for the anisotropy terms.
The dipole coupling is treated in the mean-field approximation, a procedure which we demonstrate to be a sufficiently good
approximation for realistic coupling strengths. We apply the new method to monolayers with spin and to multilayer systems with S=1. We compare some of our results to those where mean-field theory (MFT) is applied to all interactions, pointing out some
significant differences.
Received 19 June 2000 and Received in final form 2 August 2000 相似文献
47.
采用密度泛函方法(B3P86)对 Fe_2分子结构进行了优化.计算结果中未观察到自旋污染,基态波函数与高态波函数并未混杂,结果表明,Fe_2中有8个未配对电子,这些电子空间分布不同和自旋平行产生的自旋极化效应,使 Fe_2能量最低.计算结果表明,Fe_2分子的基态是~9∑_g~ ,并非~7Δ_u,进而表明 Fe_2的自旋平行效应比电子自旋配对效应要强.计算得到该分子基态的二阶、三阶和四阶力常数分别为1.4115×10~(-2)aJ/nm~2、-37.1751×10~3aJ/nm~3和 98.7596×10~4aJ/nm~4;光谱数据ω_eχ_e、B_e、α_e分别为0.3522、0.0345、 0.4963×10~(-4)cm~(-1);离解能为3.5522eV,平衡键长为0.2137nm,振动频率为292.914cm~(-1);并得到了 Murrel-Sorbie 函数. 相似文献
48.
The recent neutron scattering data for spin-wave dispersion in HoMnO3 are well-described by an anisotropic Hubbard model on a triangular lattice with a planar (XY) spin anisotropy. Best fit indicates
that magnetic excitations in HoMnO3 correspond to the strong-coupling limit U/t >∼ 15, with planar exchange energy J = 4t
2
/U ≃ 2.5 meV and planar anisotropy ΔU ≃ 0.35 meV.
相似文献
49.
Froncisz W Camenisch TG Ratke JJ Anderson JR Subczynski WK Strangeway RA Sidabras JW Hyde JS 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2008,193(2):297-304
A reference arm W-band (94 GHz) microwave bridge with two sample-irradiation arms for saturation recovery (SR) EPR and ELDOR experiments is described. Frequencies in each arm are derived from 2 GHz synthesizers that have a common time-base and are translated to 94 GHz in steps of 33 and 59 GHz. Intended applications are to nitroxide radical spin labels and spin probes in the liquid phase. An enabling technology is the use of a W-band loop-gap resonator (LGR) [J.W. Sidabras, R.R. Mett, W. Froncisz, T.G. Camenisch, J.R. Anderson, J.S. Hyde, Multipurpose EPR loop-gap resonator and cylindrical TE011 cavity for aqueous samples at 94 GHz, Rev. Sci. Instrum. 78 (2007) 034701]. The high efficiency parameter (8.2 GW−1/2 with sample) permits the saturating pump pulse level to be just 5 mW or less. Applications of SR EPR and ELDOR to the hydrophilic spin labels 3-carbamoyl-2,2,5,5-tetra-methyl-3-pyrroline-1-yloxyl (CTPO) and 2,2,6,6,-tetramethyl-4-piperidone-1-oxyl (TEMPONE) are described in detail. In the SR ELDOR experiment, nitrogen nuclear relaxation as well as Heisenberg exchange transfer saturation from pumped to observed hyperfine transitions. SR ELDOR was found to be an essential method for measurements of saturation transfer rates for small molecules such as TEMPONE. Free induction decay (FID) signals for small nitroxides at W-band are also reported. Results are compared with multifrequency measurements of T1e previously reported for these molecules in the range of 2–35 GHz [J.S. Hyde, J.-J. Yin, W.K. Subczynski, T.G. Camenisch, J.J. Ratke, W. Froncisz, Spin label EPR T1 values using saturation recovery from 2 to 35 GHz. J. Phys. Chem. B 108 (2004) 9524–9529]. The values of T1e decrease at 94 GHz relative to values at 35 GHz. 相似文献
50.
D. Dagnelund I.A. Buyanova W.M. Chen A. Murayama T. Furuta K. Hyomi I. Souma Y. Oka 《Superlattices and Microstructures》2008,43(5-6):615
Spin injection processes from a Zn0.80Mn0.20Se diluted magnetic semiconductor (DMS) to adjacent self-assembled CdSe quantum dots (QDs) were investigated by cw and time-resolved magneto-optical spectroscopy in combination with tunable laser excitation. Direct experimental evidence for the spin injection was provided from the generation of the spin polarization in the QDs, which was opposite to their expected intrinsic polarization, by resonantly generating the spins in the DMS. The observed limited spin polarization generated by the spin injection, together with the sensitivity of the spin injection efficiency on structure design, indicates severe spin loss during the process and calls for further investigations to optimize spin injection efficiency in quantum structures. 相似文献