全文获取类型
收费全文 | 16035篇 |
免费 | 3537篇 |
国内免费 | 2199篇 |
专业分类
化学 | 8937篇 |
晶体学 | 216篇 |
力学 | 855篇 |
综合类 | 144篇 |
数学 | 1492篇 |
物理学 | 10127篇 |
出版年
2024年 | 15篇 |
2023年 | 194篇 |
2022年 | 330篇 |
2021年 | 501篇 |
2020年 | 713篇 |
2019年 | 640篇 |
2018年 | 597篇 |
2017年 | 638篇 |
2016年 | 726篇 |
2015年 | 647篇 |
2014年 | 846篇 |
2013年 | 1456篇 |
2012年 | 1144篇 |
2011年 | 1160篇 |
2010年 | 982篇 |
2009年 | 1042篇 |
2008年 | 1073篇 |
2007年 | 1077篇 |
2006年 | 1031篇 |
2005年 | 879篇 |
2004年 | 846篇 |
2003年 | 744篇 |
2002年 | 753篇 |
2001年 | 560篇 |
2000年 | 514篇 |
1999年 | 386篇 |
1998年 | 376篇 |
1997年 | 295篇 |
1996年 | 215篇 |
1995年 | 202篇 |
1994年 | 175篇 |
1993年 | 129篇 |
1992年 | 146篇 |
1991年 | 104篇 |
1990年 | 83篇 |
1989年 | 67篇 |
1988年 | 70篇 |
1987年 | 53篇 |
1986年 | 52篇 |
1985年 | 62篇 |
1984年 | 37篇 |
1983年 | 23篇 |
1982年 | 47篇 |
1981年 | 26篇 |
1980年 | 21篇 |
1979年 | 14篇 |
1978年 | 23篇 |
1977年 | 16篇 |
1976年 | 12篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 859 毫秒
61.
本从第一性原理出发,计算了充磁线圈产生的磁场,脉冲充磁的超导圆盘中的感应电流密度和俘获场分布.以超导体中的电流运动方程为基础,通过磁通动力学方程E=Ec(J/Jc)^n和物质方程B=μ0H表示超导圆盘的超导特性.计算表明第一个脉冲充磁电流的峰值和磁通蠕动指数对于超导圆盘中的感应电流分布非常重要.同时研究了充磁电流的宽度,波形,第二个充磁电流的峰值和充磁线圈的形状对于俘获场的影响.计算表明不断减小脉冲充磁电流峰值的反复充磁可以保持超导圆盘中的感应电流密度的平台在一确定水平. 相似文献
62.
Magnetic Properties of the Cobaltates Na6CoS4, Na6CoSe4, and K6CoS4 The alkali metal cobalt chalcogenides Na6CoS4, Na6CoSe4, and K6CoS4 crystallize in the space group P63mc with Z = 4. The structure is characterized by isolated [CoX4]-tetrahedra. The magnetic susceptibilities show Curie-Weiss behaviour. The deviations at low temperatures are caused by antiferromagnetic interactions. The magnetic moments are discussed with regard to ligand-field parameters. 相似文献
63.
L. A. Sakhnovich 《Functional Analysis and Its Applications》2002,36(3):205-211
The conjecture according to which the mean energy of an equilibrium system in quantum theory exceeds the mean energy of the corresponding classical system is considered. It is rigorously proved that the conjecture holds for the potential well. The estimates for the mean energy of the potential well at high and low temperatures are of special interest. 相似文献
64.
Th. Gerrits H. A. M. van den Berg J. Hohlfeld O. Gielkens L. Br Th. Rasing 《Journal of magnetism and magnetic materials》2002,240(1-3):283-286
We have measured the response of a 20×10 μm, 8 nm thin NiFe (80:20) permalloy film due to excitation by short in-plane magnetic field pulses. We will show that using a two-pulse-technique a complete control of the precessional motion of the magnetisation can be achieved on picosecond timescales. Furthermore, we will present numerical calculations which show that a complete suppression of magnetisation ringing after switching can only be realised by a cascade of short field pulses. 相似文献
65.
66.
A simple model has been developed to describe the Zeeman patterns of far-infrared laser magnetic resonance spectra of the monobromomethyl radical CH2Br observed at 447.3 and 671.1μm. A satisfactory agreement between the experimental spectra of the radical and their simulation with this simple model has been achieved. This approach can be used to gain further information about the structure and the spectrum of this interesting radical. 相似文献
68.
Based on the effective-field theory with self-spin correlations and the differential operator technique,physical properties of the spin-2 system with biaxial crystal field on the simple cubic, body-centered cubic, as well as faced-centered lattice have been studied. The influences of the external longitudinal magnetic field on the magnetization,internal energy, specific heat, and susceptibility have been discussed in detail. The phenomenon that the magnetization in the ground state shows quantum effects produced by the biaxial transverse crystal field has been found. 相似文献
69.
Longlan Cui Hong Xu Ping He Keiko Sumitomo Yoshinori Yamaguchi Hongchen Gu 《Journal of polymer science. Part A, Polymer chemistry》2007,45(22):5285-5295
A hybrid emulsion polymerization was formulated for synthesizing Fe3O4/polystyrene composite latex. This system, containing binary droplets that are magnetic (Mag)‐droplets with a diameter of 100–200 nm and styrene (St)‐droplets with a diameter of 3–4 μm, was obtained by mixing Mag‐miniemulsion and St‐macroemulsion. With extremely low surfactants concentration (?critical micelle concentration, CMC), the nucleated loci are selectively controlled in the Mag‐droplets, as the result of smaller droplet size and larger surface ratio. Both water‐soluble potassium persulfate (KPS) and oil‐soluble 2,2′‐azobis(2‐isobutyronitrile) was adopted to initiate the polymerization. In the presence of KPS, magnetic polystyrene latices with particles size of 60–200 nm, narrow size distribution, and high magnetite content (86 wt % measured by TGA) were attained successfully. The synthesized magnetic Fe3O4/polystyrene latices assembled into well‐ordered hexagonal structure in the surface of a carbon supported copper grid. The influence of various parameters on various aspects of the as‐synthesized Fe3O4/polystyrene was investigated in detail: type of initiator on composite morphology, feed ratio of Mag‐miniemulsion and St‐macroemulsion on magnetite content, and hydrophobic agent or amount of surfactant on size and size distribution. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5285–5295, 2007 相似文献
70.
认为物质的质量(能量)存在形式可分为两部分,一部分是以纯物质形式存在的,另一部分是以纯重力场形式存在的.物质质量(能量)这两种形式各自对应着相应的能量 动量张量,物质总的能量-动量张量可表示为Tμν=T(Ⅰ)μν+T(Ⅱ)μν,这里,T(Ⅰ)μν,T(Ⅱ)μν分别代表物质纯物质部分和纯重力场部分的能量-动量张量.通过类比电磁理论,定义:ωμ≡-c2gμ0/g00,并引入一个反对称张量Dμν=ωμ/xν-ων/xμ,则物质纯重力场部分的能量-动量张量为T(Ⅱ)μν=(DμρDρν-gμνDαβDαβ/4
关键词:
能量-动量张量
纯重力场
重力场方程
标量重力势
矢量重力势 相似文献