全文获取类型
收费全文 | 2223篇 |
免费 | 370篇 |
国内免费 | 107篇 |
专业分类
化学 | 512篇 |
晶体学 | 50篇 |
力学 | 304篇 |
综合类 | 3篇 |
数学 | 68篇 |
物理学 | 1224篇 |
综合类 | 539篇 |
出版年
2024年 | 2篇 |
2023年 | 20篇 |
2022年 | 40篇 |
2021年 | 54篇 |
2020年 | 75篇 |
2019年 | 52篇 |
2018年 | 59篇 |
2017年 | 64篇 |
2016年 | 99篇 |
2015年 | 69篇 |
2014年 | 90篇 |
2013年 | 185篇 |
2012年 | 155篇 |
2011年 | 176篇 |
2010年 | 100篇 |
2009年 | 130篇 |
2008年 | 107篇 |
2007年 | 115篇 |
2006年 | 116篇 |
2005年 | 114篇 |
2004年 | 98篇 |
2003年 | 89篇 |
2002年 | 93篇 |
2001年 | 75篇 |
2000年 | 77篇 |
1999年 | 72篇 |
1998年 | 67篇 |
1997年 | 63篇 |
1996年 | 38篇 |
1995年 | 26篇 |
1994年 | 28篇 |
1993年 | 31篇 |
1992年 | 23篇 |
1991年 | 18篇 |
1990年 | 27篇 |
1989年 | 11篇 |
1988年 | 9篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1976年 | 1篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有2700条查询结果,搜索用时 312 毫秒
151.
Karen B. Paul 《Central European Journal of Physics》2007,5(1):11-24
Fe(2 ML)/V(y ML) and interleaved Fe(2 ML)/V(y ML)/Fe(3 ML)/V(y ML) superlattice systems with spacer thicknesses, y, (4 ≤ y ≤ 17) were investigated macro-magnetically to estimate the coupling strength and the magnetoresistance in these materials,
and particularly in the antiferromagnetically coupled monolayers. The results from the magnetic and magnetoresistive measurements
indicate that adding one monolayer of Fe increases the antiferromagnetic coupling and the magnetoresistivity ratio from 0.0075
mJ/m2 at 20 K and 2 % at 10 K for Fe(2 ML)/V(y ML), to 0.05 mJ/m2 and 2.5 % for Fe(2 ML)/V(y ML)/Fe(3 ML)/V(y ML) at the same temperatures. Both systems exhibit in-plane magnetic and magnetoresistive isotropy, therefore the increase
of the conferred physical parameters is attributed mainly to the stresses at the interface as governing mechanisms over the
magnetoelastic forces.
相似文献
152.
Boltzmann-transport equation is analytically solved for two-component magnetoplasma using Chapman-Enskog analysis to include
collisional diffusion transport having anisotropies in both streaming velocity and temperature components. The modified collisional
integrals are analytically solved with flux integrals and perturbed kinetic equation to arrive at drift diffusion velocity
and resulting transport coefficients which are markedly affected by both streaming and temperature anisotropy. The early isotropic
results are recovered in the limit V
0 = 0 and T
‖ = T
⊥ which reduce to eqs (11.30) and (11.31) of [1] and eqs (2.7) and (2.13) of [2]. The electrical resistivity (η⊥) diminishes sharply in fusion temperature limit kT
⊥ = 1 keV. The shape of the curves for both electrical resistivity and thermal conductivity is rectangular hyperbolic. However,
for low thermal ratio (T
‖/T
⊥ < 1), the curves are raised up and for high thermal ratio (T
‖/T
⊥ > 1), they are lowered down the isotropic case (T
‖/T
⊥ > 1), showing comparatively diminished magnitudes of the quantities.
相似文献
153.
晶粒间界相对纳米Nd_2Fe_(14)B各向异性和矫顽力的影响 总被引:1,自引:0,他引:1
本文采用立方晶粒结构模型研究了晶粒间界相对纳米硬磁材料各向异性和矫顽力的影响.结果表明:晶粒间界相减弱了交换耦合作用.当晶粒尺寸D为定值时,随着晶粒间界相厚度d的增加,晶粒平均各向异性单调增加,而材料的有效各向异性Keff、矫顽力单调减小.我们计算的矫顽力随晶粒尺寸的变化与相关理论和实验结果基本一致. 相似文献
154.
M. Patra K. De S. Majumdar S. Giri 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(4):367-371
We observe the negative shift of the magnetic hysteresis loop at 5 K, while the sample is cooled in external magnetic field
in case of 30% of Fe substitution in LaMnO3. The negative shift and training effect of the hysteresis loops indicate the phenomenon of exchange bias. The cooling field
dependence of the negative shift increases with the cooling field below 7.0 kOe and then, decreases with further increase
of cooling field. The temperature dependence of the negative shift of the hysteresis loops exhibits that the negative shift
decreases sharply with increasing temperature and vanishes above 20 K. Temperature dependence of dc magnetization and ac susceptibility
measurements show a sharp peak (Tp) at 51 K and a shoulder (Tf) around 20 K. The relaxation of magnetization shows the ferromagnetic and glassy magnetic components in the relaxation process,
which is in consistent with the cluster-glass compound. 相似文献
155.
M. C. Desjonquères C. Barreteau G. Autès D. Spanjaard 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(1):23-27
We show that considerable orbital magnetic moments and magneto-crystalline anisotropy energies are obtained for a Fe monatomic
wire described in a tight-binding method with intra-atomic electronic interactions treated in a full Hartree Fock (HF) decoupling
scheme.
Even though the use of the orbital polarization ansatz with simplified Hamiltonians leads to fairly good results when the
spin magnetization is saturated this is not the case of unsaturated systems. We conclude that the full HF scheme is necessary
to investigate low dimensional systems. 相似文献
156.
岩心磁组构分析古水流方向的原理与应用 总被引:1,自引:0,他引:1
目的针对鄂尔多斯盆地天环拗陷南段延长组开展磁组构古水流研究。方法通过测量岩心样品的磁化率各向异性,分析磁组构特征,结合矿物岩石学特征综合开展岩心古水流方向判识。结果延长组碎屑岩的古水流方向为NE—SW,NW—SE和NS向,分别代表西南、西北和北部3个方向的物质供给。结论磁组构分析古水流方向与轻重矿物组合法判断的物源方向一致,表明应用磁组构分析钻井岩心古水流方向的方法是可行、可靠的,利用磁组构分析方法恢复古水流方向,判识物源具有较好的应用前景。 相似文献
157.
Exchange-coupling interaction, effective anisotropy and magnetic property of nano-magnetic materials
The theories and models of exchange-coupling interaction between grains in nanocrystalline magnetic materials are introduced here. Their insufficiencies and distinctions from the experimental results are pointed out, and some revisions are made. The effects of the phase component ratio, the grain size and microstructure on the effective anisotropy and magnetic properties in the nanocomposite permanent materials and the improved models are discussed in detail. 相似文献
158.
Summary Exact solutions are obtained in the framework of the classical theory of laminates subjected to the action of normal moments,
double forces, double moments or momentless double dipoles. Seven cases of such loads are considered and completed by considering
the case of given transversal discontinuity of normal deflection. It is shown that, in contrast to the case of infinite straight
dislocations in a pure in-plane problem, the energy of this eighth solution depends on the discontinuity orientation. Some
numerical examples are presented. Besides the formal value, the obtained double-force and double-moment solutions, as well
as dimensionless double dipoles, can be used to construct kernels of additional boundary integral equations (BIE). Due to
the coupling phenomena in the BIE system for the region with a corner point, additional variable such as corner forces appear
and require the mentioned equation.
Received 22 June 1999; accepted for publication 6 March 2000 相似文献
159.
V. V. Lasukov 《Russian Physics Journal》2009,52(1):1-10
It is shown that anisotropy of relict radiation can be caused by anisotropy of a relict scalar field, and large-scale structures
of the relict scalar field can lead to large-scale structures of baryon matter.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 3–11, January, 2009. 相似文献
160.
在微裂缝油藏开发过程中 ,油藏流体压力的上升或下降会导致微裂缝的张开或闭合 ,油藏的绝对渗透率随之发生变化 ,而且微裂缝的存在使油藏渗透率呈现较强的各向异性 ,从而影响油藏的开发。针对这些特性 ,分析了微裂缝的存在对油藏绝对渗透率大小和主轴方向的影响 ,建立了含天然微裂缝低渗透油藏的三维、三相数学模型及数值模拟模型 ,并在此基础上研制出了油藏模拟软件。运用该软件进行了典型油藏单元的实例计算 ,结果表明 ,开采初期微裂缝油藏日产油量比常规油藏高 ,而后期则比常规油藏低 ,且采出程度总比常规油藏高 相似文献