全文获取类型
收费全文 | 672篇 |
免费 | 37篇 |
国内免费 | 30篇 |
专业分类
化学 | 77篇 |
晶体学 | 4篇 |
力学 | 18篇 |
综合类 | 10篇 |
数学 | 30篇 |
物理学 | 600篇 |
出版年
2023年 | 4篇 |
2022年 | 6篇 |
2021年 | 15篇 |
2020年 | 12篇 |
2019年 | 16篇 |
2018年 | 14篇 |
2017年 | 9篇 |
2016年 | 13篇 |
2015年 | 19篇 |
2014年 | 30篇 |
2013年 | 31篇 |
2012年 | 72篇 |
2011年 | 68篇 |
2010年 | 65篇 |
2009年 | 58篇 |
2008年 | 59篇 |
2007年 | 21篇 |
2006年 | 33篇 |
2005年 | 24篇 |
2004年 | 16篇 |
2003年 | 10篇 |
2002年 | 31篇 |
2001年 | 8篇 |
2000年 | 19篇 |
1999年 | 11篇 |
1998年 | 19篇 |
1997年 | 10篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1969年 | 1篇 |
排序方式: 共有739条查询结果,搜索用时 78 毫秒
81.
Results for the one-loop calculation of the decay width Γ(H→ggZ) in the standard model with Higgs boson masses in the range 115 GeV<m
H
<2m
W
are presented. We find that among all the helicity amplitudes contributing to the width only those for which the gluons have
the same polarization and the Z is longitudinally polarized contribute in any significant way. The calculation includes all contributions from the second
and third generations, and kinematic cuts to enhance the H→ggZ signal. Compared to the width of H→gg, we find Γ(H→ggZ)/Γ(H→gg)≲10−4. 相似文献
82.
The physical properties of magnetic domain walls and electrical conductivity of permalloy thin films under external magnetic fields were studied. Using a magnetic force microscope (MFM), we observed the variation of domain configurations with the change of applied magnetic field for different film thicknesses of 245, 320, and 415 nm. A superconducting quantum interference device (SQUID) was exploited to measure the magnetization loop for the applied magnetic field either parallel or perpendicular to the normal direction of the surface. We also found that the resistivity increases significantly as the electrical current conduction changed from parallel to perpendicular to the domain walls. 相似文献
83.
Cobalt ferrite (CoFe2O4) nano-particles have been synthesized successfully and we studied the effect of temperature on them. The particles have been annealed at different temperatures ranging from 373 to 1173 K. Significant effect on the physical parameters like crystalline phase, crystallite size, particle size, lattice strain and magnetic properties of the nano-particles has been investigated. The studies have been carried out using a powder X-ray diffractometer (XRD), a transmission electron microscope (TEM) and a vibrating sample magnetometer (VSM). A thorough study of the variation of specific surface area and particle size with annealing is presented here, with their effects on saturation magnetization. 相似文献
84.
The wide chemical shift dispersion and long T(1) of (13)C have allowed determination of in vivo magnetization transfer effects caused by aspartate aminotransferase and lactate dehydrogenase reactions using (13)C magnetic resonance spectroscopy. In this report, we demonstrate that these effects can be observed in the proton spectra by transferring the equilibrium magnetization of (13)C via the one-bond scalar coupling between (13)C and (1)H using an inverse insensitive nuclei enhanced by polarization transfer-based heteronuclear polarization transfer method. This inverse method allows a combination of the advantages of the long (13)C T(1) for maximum magnetization transfer and the high sensitivity of proton detection. The feasibility of this in vivo inverse polarization transfer approach was evaluated for detecting the (13)C magnetization transfer effect of aspartate aminotransferase and lactate dehydrogenase reactions from a 72.5-microl voxel in the rat brain at 11.7 T. 相似文献
85.
86.
Software aging is a phenomenon referring to the performance degradation of a long-running software system. This phenomenon is an accumulative process during execution, which will gradually lead the system from a normal state to a failure-prone state. It is a crucial challenge for system reliability to predict the Aging-Related Failures (ARFs) accurately. In this paper, permutation entropy (PE) is modified to Multidimensional Multi-scale Permutation Entropy (MMPE) as a novel aging indicator to detect performance anomalies, since MMPE is sensitive to dynamic state changes. An experiment is set on the distributed database system Voldemort, and MMPE is calculated based on the collected performance metrics during execution. Finally, based on MMPE, a failure prediction model using the machine learning method to reveal the anomalies is presented, which can predict failures with high accuracy. 相似文献
87.
A nanoisland consists of center spin-5/2 and perimeter spin-3/2 atoms, which is described by transverse Ising model with single-ion anisotropy. Magnetic behaviors of the nanoisland are studied by the effective-field theory with correlations and the differential operator technique. The formulas of the magnetization and the phase transition of the system are given. The numerical results of the phase transition, the magnetization, the initial susceptibility and the internal energy have been discussed. Some interesting phenomena, such as a new reentrant, are found. Namely there are multitransition temperatures dependent on competition among the single-ion anisotropies, the transverse field and the interlayer coupling. These results can provide some guidance to structure design in the nanoislands. 相似文献
88.
Single phase samples of bulk GdCr1-xFexO3 were prepared for x = 0 to 0.50. The lattice parameters obtained from Rietveld refinement based on Pbnm space group show that they increase systematically with Fe concentration, i.e. with a = 5.3145 Å, b = 5.5249 Å and c = 7.6068 Å for x = 0 to a = 5.3330 Å, b = 5.5670 Å, and c = 7.6382 Å for x = 0.50. Magnetization measurement shows that all samples exhibit antiferromagnetic transition. Their Neel temperature (TN) gradually decreases upto x = 0.20 and beyond that it increases quite sharply due to considerable concentration of Fe3+ – O2− – Fe3+ networks. The magnetization reversal observed in the parent compound (GdCrO3) is found to be suppressed upon Fe substitution and however for x = 0.40, magnetic compensation is observed at Tcomp = 125 K. They are explained by considering the variation in the magnitude of weak ferromagnetic moment for different Fe concentrations. Complex impedance spectra measured at different temperatures above room temperature show the thermally activated relaxation of charge carriers with contribution from both grains and grain boundaries. The relaxation frequency of charge carriers and dc conductivity follow the Arrhenius law with comparable activation energy values. 相似文献
89.
M.A. Continentino J.C. Fernandes R.B. Guimar aes H.A. Borges A. Sulpice J.-L. Tholence J.L. Siqueira J.B.M. da Cunha C.A. dos Santos 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(4):613-618
The system Cu2FeO2BO3 is an oxyborate belonging to the family of the ludwigites. In this paper we present AC susceptibility, magnetization measurements
and M?ssbauer spectroscopy on this material which allows for a complete characterization of its complex magnetic behavior.
We find an hierarchy of interactions which clearly defines three regimes with decreasing temperature. These are associated
with, the freezing of the Fe moments, the antiferromagnetic ordering of the Cu sub-lattice and finally the coupling between
both systems.
Received 25 September 1998 相似文献
90.
A double-well potential model is established to explain the dielectric anomaly of ferroelectrics. The dielectric constant
consists of two parts. One part is independent of the long-range correlation, following 1/T law. The other part originates
from the long-range correlation, and can be described by the correlation length well. The deviation from Curie-Weiss law in
a small size sample originates from the decrease of the long-range correlation.
Project supported by the Climbing Program of Foundamental Research of China. 相似文献