全文获取类型
收费全文 | 10160篇 |
免费 | 1966篇 |
国内免费 | 749篇 |
专业分类
化学 | 974篇 |
晶体学 | 43篇 |
力学 | 230篇 |
综合类 | 129篇 |
数学 | 206篇 |
物理学 | 3073篇 |
无线电 | 8220篇 |
出版年
2024年 | 53篇 |
2023年 | 128篇 |
2022年 | 225篇 |
2021年 | 248篇 |
2020年 | 305篇 |
2019年 | 184篇 |
2018年 | 225篇 |
2017年 | 329篇 |
2016年 | 452篇 |
2015年 | 455篇 |
2014年 | 746篇 |
2013年 | 715篇 |
2012年 | 803篇 |
2011年 | 796篇 |
2010年 | 622篇 |
2009年 | 574篇 |
2008年 | 679篇 |
2007年 | 751篇 |
2006年 | 695篇 |
2005年 | 592篇 |
2004年 | 537篇 |
2003年 | 496篇 |
2002年 | 440篇 |
2001年 | 350篇 |
2000年 | 275篇 |
1999年 | 210篇 |
1998年 | 181篇 |
1997年 | 120篇 |
1996年 | 129篇 |
1995年 | 107篇 |
1994年 | 108篇 |
1993年 | 63篇 |
1992年 | 60篇 |
1991年 | 51篇 |
1990年 | 36篇 |
1989年 | 33篇 |
1988年 | 31篇 |
1987年 | 10篇 |
1986年 | 9篇 |
1985年 | 17篇 |
1984年 | 15篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1973年 | 2篇 |
1957年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
992.
Lutful Bari Bhuiyan 《Molecular physics》2013,111(15):1863-1871
A generalised form of a local contact condition for the charge profile in a primitive model planar double layer [Bhuiyan, Outhwaite, and Henderson, Mol. Phys. 107, 343 (2009)] at low electrode charge is examined for completely asymmetric, binary electrolytes. The cation and anion sizes are taken to be different from each other with the valencies being 2+:1? or 1+:2?, while the electrode surface charge density is varied from being negative through zero to being positive. Monte Carlo simulation data obtained for such double layer systems at varying ionic radius ratios and electrolyte concentrations suggest the generalised contact relation to be valid at low charge on the electrode. 相似文献
993.
R. E. Raab 《Molecular physics》2013,111(23-24):3051-3056
The quadrupole–quadrupole polarizability of a molecule introduced by Buckingham is not a unique molecular property, in the sense that it depends on an arbitrary choice of the origin of the molecular coordinates. To obtain a physically acceptable form of this property for a non-magnetic molecule, a linear combination is taken of molecular polarizabilities of the relevant multipole order (electric octopole-magnetic quadrupole). By requiring this combination to possess the desired space–time and symmetry properties, as well as origin independence, an acceptable quadrupole–quadrupole polarizability is obtained. Expressions are presented for the components of this polarizability for molecules of certain symmetries. 相似文献
994.
The acetone molecule is investigated in its ground state and valence 1,3n-π*, 1,3π-π*, and 1,3σ-π* excited states and Rydberg 1,3n-3s, 1,3π-3?, 1,3n-3py and 1,3π-3py states using the CASSCF, CASPT2, and CCSD(T) methods. Equilibrium geometries of excited states are obtained and their changes with respect to the ground state are discussed. For most excited states the C2v symmetry of the ground state is lowered to the Cs symmetry. A series of valence vertical and adiabatic excitation energies is presented along with excitation energies for Rydberg states. The main body of the paper contains Finite-Field Perturbation Theory (FFPT) calculations of electric properties of the vertically as well as geometry relaxed excited states. Dipole moments of valence excited states decrease significantly upon excitation, being about one half of the ground state dipole moment. Polarizabilities usually change upon excitation much less (increase by about 30%) but hyperpolarizabilities are enhanced up to one or two orders of magnitude. The orientation of the dipole moment is reversed in some vertically excited Rydberg states. Properties of the ground and excited states are discussed considering alterations of the electronic structure and shifts in the geometry. 相似文献
995.
The implementation of a heating element to a composite gasket for high-temperature applications in the diamond-anvil cell was developed based on a double-gasket assemblage. The heating element is a thin platinum wall that covers the central borehole of the metal–ceramic–metal composite gasket and interconnects the two metal component parts of the gasket. Applying electric powers up to 35 W to the two gasket metal components result in ring-like heating around the sample inside the pressure chamber with temperatures exceeding ~2000 K in individual cases. The ring-like distribution of the maximum temperature located at the pressure-chamber wall facilitates a homogeneous temperature distribution at the sample position. As a consequence of the concentration of the heating power to the pressure chamber region, gradients of surface temperatures, both at the gasket and the diamond anvil, appear to be more pronounced compared with those known for classical external electrical heating. Apart from the tests of the mechanical stability on high-pressure operation in the diamond anvil cell at room temperature, the influence of the anvils in contact with the gasket on the characteristic power–temperature curves, temperature gradients and thermal equilibration resulting from changes in electrical power settings have been evaluated within the scope of a series of experimental investigations. 相似文献
996.
通过高速摄影系统对电火花气泡与不同沙粒底面间的相互作用进行了实验研究,并改变气泡与沙粒底面之间的距离.实验结果表明:气泡在与沙粒底面的相互作用中会产生两种明显不同的现象,即形成与近刚性壁面类似的气泡射流以及“蘑菇状”气泡,“蘑菇状”气泡撕裂形成两个气泡,随后产生两个反方向的沿轴线方向的射流.沙粒底面边界具有刚性与弹性两种特征.另外,随着气泡与沙粒底面之间的距离d的增大,气泡脉动周期先增大然后减小,存在气泡脉动周期峰值.对于不同的沙粒底面边界,出现气泡脉动周期峰值的距离d随着沙底粒径的增大而越小. 相似文献
997.
998.
999.
热场致发射阴极所产生的强流电子束具有很强的空间电荷效应,为研究该效应对热场致发射过程中诺廷汉(Nottingham)效应的影响机理,在理论分析的基础上,用数值方法研究了不同逸出功和多个外加电场条件下考虑空间电荷效应对诺廷汉效应结果的影响,并与不考虑空间电荷效应时的情形进行了对比. 结果表明:空间电荷效应的强弱会显著影响到阴极表面的稳态电场,进而对诺廷汉效应产生不可忽略的影响;当逸出功在3.0–4.52 eV、外加电场在3×109–9×109 V/m范围内时,考虑空间电荷效应的影响后,热场致发射电子所带走的平均能量较不考虑空间电荷效应时增加0–2.5 eV,且温度越高或外加电场越大时,该增加值越大;考虑空间电荷效应对诺廷汉效应的影响后,热场致发射电子从阴极带走的平均能量随外加电场的增加呈非线性下降规律;当阴极表面温度较高时,诺廷汉效应中的冷却效应随二极管间隙距离的变大而增强.
关键词:
热场致发射
诺廷汉效应
空间电荷效应
阴极表面电场 相似文献
1000.
基于分数阶混沌系统稳定性理论, 设计高效的非线性控制器, 实现初始值不同的两个分数阶Chua's系统错位投影同步. 根据分数阶复频域近似方法, 提出分数阶系统的等效电路, 实现分数阶Chua's系统错位投影同步的无感模块化电路. 最后,利用改进的混沌掩盖通信原理, 将以上同步方案应用于混沌保密通信中, 在发送端使用分数阶混沌序列对有用信号加密传送, 从接收端可以无失真地恢复出有用信号. 数值仿真与电路仿真证实了提出方案的可行性.
关键词:
分数阶Chua's系统
错位投影同步
无感模块化电路
保密通信 相似文献