全文获取类型
收费全文 | 5044篇 |
免费 | 723篇 |
国内免费 | 280篇 |
专业分类
化学 | 2364篇 |
晶体学 | 212篇 |
力学 | 232篇 |
综合类 | 18篇 |
数学 | 147篇 |
物理学 | 3074篇 |
出版年
2024年 | 12篇 |
2023年 | 39篇 |
2022年 | 82篇 |
2021年 | 86篇 |
2020年 | 96篇 |
2019年 | 90篇 |
2018年 | 104篇 |
2017年 | 149篇 |
2016年 | 218篇 |
2015年 | 154篇 |
2014年 | 243篇 |
2013年 | 565篇 |
2012年 | 305篇 |
2011年 | 410篇 |
2010年 | 340篇 |
2009年 | 378篇 |
2008年 | 354篇 |
2007年 | 323篇 |
2006年 | 353篇 |
2005年 | 247篇 |
2004年 | 188篇 |
2003年 | 171篇 |
2002年 | 208篇 |
2001年 | 102篇 |
2000年 | 114篇 |
1999年 | 120篇 |
1998年 | 83篇 |
1997年 | 60篇 |
1996年 | 55篇 |
1995年 | 63篇 |
1994年 | 41篇 |
1993年 | 38篇 |
1992年 | 29篇 |
1991年 | 20篇 |
1990年 | 18篇 |
1989年 | 21篇 |
1988年 | 9篇 |
1987年 | 15篇 |
1986年 | 13篇 |
1985年 | 19篇 |
1984年 | 17篇 |
1983年 | 7篇 |
1982年 | 15篇 |
1981年 | 19篇 |
1980年 | 5篇 |
1978年 | 16篇 |
1977年 | 3篇 |
1976年 | 7篇 |
1975年 | 6篇 |
1973年 | 8篇 |
排序方式: 共有6047条查询结果,搜索用时 9 毫秒
61.
D. Bourret M. Alyari J. Regnier R. Sempere J. Zarzycki 《International Journal of Infrared and Millimeter Waves》1984,5(11):1483-1491
A Q band interferometer for determining the complex permittivity of solids and liquids between 20°C and 1300°C has been developed. The Roberts and Von Hippel standing-wave method was used. The technique involves the utilization of a computer-assisted digital voltmeter for data acquisition and treatment. Results for a 67SiO2–33Na2O within the temperature range 20–400°C and in the liqid state (950°C) are presented. 相似文献
62.
脉冲激光在液体中激发的声波特性研究 总被引:1,自引:0,他引:1
理论上分析了脉冲激光在液体中产生的声波波阵面随光声源形状的变化,以及不同激发机制下光声脉冲波形的差别,并从实验中得出了脉冲CO2激光光声脉冲频谱特性.结果表明光声波波阵面为球面或柱面,热弹机制激发双极性的光声脉冲,汽化机制激发单极性的光声脉冲,CO2脉冲激光在水中激发的声波频谱峰值主要在100 kHz以下.通过选择光声源的形状和激发机制可以获得所需的光声信号. 相似文献
63.
64.
利用转移矩阵方法对二维正方介质柱光子晶体的传输特性进行了研究,数值计算研究了不同晶格、同一晶格柱体截面面积不同、放置方位角不同时光子晶体的传输特性。数值结果表明光子禁带的宽度与中心频率和晶格结构有很大关系,正方晶格更易形成平坦光子禁带,柱体截面面积大,则形成的禁带较宽,在其他因素相同的条件下柱体放置的方位角对光子禁带有重要影响。数值研究表明在正方介质柱下设计宽平坦光子禁带时,可以首先考虑正方晶格结构,其次设法使柱体截面尽量大一些,最后可通过柱体放置方位角来微调光子禁带的宽度与中心频率以达到设计要求。 相似文献
65.
Considering external electric field as well as third- and fourth-order phonon anharmonic interaction terms in the pseudospin-lattice
coupled mode (PLCM) model Hamiltonian for KDP-type ferroelectrics, expressions for field-dependent shift, width, renormalized
soft mode frequency, Curie temperature, dielectric constant and dielectric loss are evaluated. For the calculation, method
of statistical double-time temperature-dependent Green’s function has been used. By fitting model values of physical quantities,
temperature and electric field dependences of soft mode frequency, dielectric constant and loss have been calculated which
compare well with experimental results of Baumgartner [8] and Choi and Lockwood [9]. Both dielectric constant and loss decrease
with electric field. 相似文献
66.
67.
Dielectric relaxation study of the binary mixtures of poly(vinyl pyrrolidone) (PVP) (Mw=24000, 40000 and 360000 g mol−1) with ethyl alcohol (EA) and poly(ethylene glycol)s (PEGs) (Mw=200 and 400 g mol−1) in dilute solutions of dioxane were carried out at 10.1 GHz and 35°C. The relaxation time of PVP-EA mixtures was interpreted
by the consideration of a wait-and-switch model in the local structure of self-associated ethyl alcohol molecules and also
the PVP chain length as a geometric constraint for the reorientational motion of ethyl alcohol molecules. The formation of
complexes and effect of PVP chain length on the molecular dynamics, chain flexibility and stretching of PEG molecules in PVP-PEG
mixtures were explored from the comparative values of dielectric relaxation time. Further, relaxation time values in dioxane
and benzene solvent confirm the viscosity independent molecular dynamics in PVP-EA mixtures but the values vary significantly
with the non-polar solvent environment. 相似文献
68.
We study theoretically a nonlinear response of the planar metal/dielectric nanostructures constituted from periodical array
of ultra thin silver layers and the layers of Kerr-like nonlinear dielectric. We predict hysteresis-type dependences of the
components of the tensor of effective dielectric permittivity on the field intensity allowing the change in material transmission
properties from transparent to opaque and back at extremely low intensities of the light. It makes possible to control the
light by light in all-optical nanoscale devices and circuits. 相似文献
69.
The variation of DC electrical conductivity and the optical properties of thermally evaporated a- (Sb2Se3)100−xSnx thin films with temperature have been studied. It is found that the thermal activation energy decreases, while the optical gap first increases (up to x=1) and then decreases, with the increase in Sn content. These results have been explained by taking into consideration the structural modifications induced by the incorporation of Sn into the parent alloy. The variation in the conductivity prefactor (σo) with Sn addition indicates a change in the dominant conduction transport mechanism from extended states to localized states. An experimental correlation between the activation energy and the pre-exponential factor has been observed, indicating the validity of Meyer–Neldel rule in the studied samples. 相似文献
70.
从压力波法测量平板样本中空间电荷分布的理论分析出发,提出了对于同轴结构的固体电介质中空间电荷分布的压力波法测量的物理模型,并得出了测量电流的解析的数学表达式.依据泊松方程,考虑样品内的电场强度、介电常数和空间电荷密度随外界声波扰动而发生变化,将圆柱试样受到的压力波的影响分解成样品形变和质点位移两部分,进而得到了以同轴结构中空间电荷分布的压力波法测量的电压与电流表达式.测量电流的数学表达式表明,对于同轴结构,压力波法的测量电流信号不像平板结构中那样基本正比于空间电荷分布,而是应该做进一步的修正处理. 相似文献