全文获取类型
收费全文 | 20113篇 |
免费 | 2422篇 |
国内免费 | 1635篇 |
专业分类
化学 | 13907篇 |
晶体学 | 227篇 |
力学 | 926篇 |
综合类 | 104篇 |
数学 | 2613篇 |
物理学 | 6393篇 |
出版年
2023年 | 312篇 |
2022年 | 353篇 |
2021年 | 505篇 |
2020年 | 609篇 |
2019年 | 610篇 |
2018年 | 491篇 |
2017年 | 514篇 |
2016年 | 815篇 |
2015年 | 807篇 |
2014年 | 1004篇 |
2013年 | 1301篇 |
2012年 | 1647篇 |
2011年 | 1797篇 |
2010年 | 1150篇 |
2009年 | 1124篇 |
2008年 | 1284篇 |
2007年 | 1142篇 |
2006年 | 1060篇 |
2005年 | 939篇 |
2004年 | 860篇 |
2003年 | 694篇 |
2002年 | 630篇 |
2001年 | 515篇 |
2000年 | 400篇 |
1999年 | 390篇 |
1998年 | 287篇 |
1997年 | 233篇 |
1996年 | 252篇 |
1995年 | 244篇 |
1994年 | 240篇 |
1993年 | 188篇 |
1992年 | 170篇 |
1991年 | 152篇 |
1990年 | 171篇 |
1989年 | 131篇 |
1988年 | 123篇 |
1987年 | 85篇 |
1986年 | 98篇 |
1985年 | 110篇 |
1984年 | 85篇 |
1983年 | 83篇 |
1982年 | 60篇 |
1981年 | 55篇 |
1980年 | 49篇 |
1979年 | 38篇 |
1977年 | 40篇 |
1976年 | 39篇 |
1975年 | 37篇 |
1974年 | 50篇 |
1973年 | 48篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
31.
Uhm H.S. Lee P.H. Kim Y.I. Kim J.H. Chang H.Y. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1995,23(4):628-635
A theory is developed for the density profile of low temperature plasmas confined by applied magnetic field and an experiment of the electron-cyclotron-resonance (ECR) plasma is conducted to compare the theoretical prediction and experimental measurements. Due to a large electron mobility along the magnetic field, electrons move quickly out of the system, leaving ions behind and building a space charge potential, which leads to the ambipolar diffusion of ions. In a steady-state condition, the plasma generation by ionization of neutral molecules is in balance with plasma loss due to the diffusion, leading to the electron temperature equation, which is expressed in terms of the plasma size, chamber pressure, and the ionization energy and cross section of neutrals. The power balance condition leads to the plasma density equation, which is also expressed in terms of the electron temperature, the input microwave power and the chamber pressure. It is shown that the plasma density increases, reaches its peak and decreases, as the chamber pressure increases from a small value (0.1 mTorr). These simple expressions of electron temperature and density provide a scaling law of ECR plasma in terms of system parameters. After carrying out an experimental observation, it is concluded that the theoretical predictions of the electron temperature and plasma density agree remarkably well with experimental data 相似文献
32.
Zhong Yin Xiao 《International Journal of Infrared and Millimeter Waves》2006,27(6):847-855
A new compact bandpass filter composed of two coupled linear tapered line resonators (LTLRs) is designed. The two resonators
are arranged in different layers. The filter has two transmission zeros on both sides of the passband. It has small size and
steep response below its passband. It is also shown that this filter has 0.6 dB low insertion loss at the centre frequency
and 10.5% 3dB bandwidth.
This work was supported by the Development Foundation of Shanghai Educational Committee (217608) and Shanghai Leading Academic
Discipline Project (T0102). 相似文献
33.
应用不可约张量理论构造了三角对称晶场中3d2/3d8态离子的45阶可完全对角化的微扰哈密顿矩阵,研究了CsNiCl3晶体的光谱精细结构、晶体结构、零场分裂参量、Jahn-Telller效应以及自旋单重态对Ni2+离子基态能级的影响,理论与实验相符合.在此基础上,进一步研究了以前工作中被忽略的自旋-自旋耦合作用和Trees修正对CsNiCl3晶体的光谱精细结构和零场分裂参量的影响,发现有四种机理会影响零场分裂参量:1)自旋-轨道耦合机理,2)自旋-自旋耦合机理;3)自旋-轨道与自旋-自旋联合耦合机理;4)自旋-轨道与Trees修正联合耦合机理,其中自旋-轨道耦合机理是最主要的,其他三种机理也是不可忽略的.
关键词:
基态能级
精细结构
零场分裂
自旋-自旋耦合 相似文献
34.
在弱场图像下,利用Racah不可约张量算符方法得到了三角对称3d4/3d6电子组态的210阶可完全对角化的微扰哈密顿矩阵、最近邻点电荷模型晶体结构常量公式和电子顺磁共振g因子公式.研究了LiCoO2晶体和掺入Ni的LiCoO2:Ni晶体中Co3+的基态能级、晶体结构和电子顺磁共振g因子.考虑了LiCoO2晶体和LiCoO2:Ni晶体中自旋单重态和三重态对Co3+基态能级的影响,讨论了LiCoO2晶体和在LiCoO2晶体中掺杂Ni后Co3+局域结构常量大小的变化是引起Co3+的基态能级变化的主要原因,理论和实验都证实了这一点.还计算了掺杂前后的电子顺磁共振g因子,计算结果与实验值符合得较好. 相似文献
35.
Gauss periods give an exponentiation algorithm that is fast for many finite fields but slow for many other fields. The current paper presents a different method for construction of elements that yield a fast exponentiation algorithm for finite fields where the Gauss period method is slow or does not work. The basic idea is to use elements of low multiplicative order and search for primitive elements that are binomial or trinomial of these elements. Computational experiments indicate that such primitive elements exist, and it is shown that they can be exponentiated fast. 相似文献
36.
Jun-tao Chang Joerg Evers Marian O. Scully M. Suhail Zubairy 《量子光学学报》2006,12(B08):77-77
We propose a scheme to obtain the distance of two identical atoms placed inside the standing wave field by monitoring the collective resonance fluorescence spectrum emitted by the two particles. We find three different parameter ranges, depending on the distance of the atoms as compared to the transition wavelength. For large interparticle distances, dipole-dipole coupling is negligible, and the main system evolution arises from the interaction with the standing wave field. In the small-distance limit, the dynamics is dominated by the dipole-dipole interaction. Finally, in the intermediate region, a rich interplay of the various couplings arises, which however is lifted for strong driving laser fields. The present measurement procedure allows us to distinguish the three cases. In each of the cases, we show how to determine the distance of the two particles and their respective positions relative to the nodes of the standing wave field with fractional-wavelength precision. 相似文献
37.
Qian-shun Chang Bo-ling GuoInstitute of Applied Mathematics Academy of Mathematics System Sciences Chinese Academy of Sciences Beijing ChinaInstitute of Applied Physics Computational Mathematics Beijing China 《应用数学学报(英文版)》2002,18(2):201-214
Abstract In this paper, a dissipative Zakharov equations are discretized by difference method.We make priorestimates for the algebric system of equations. It is proved that for each mesh size,there exist attractors forthe discretized system.The bounds of the Hausdorff dimensions of the discrete attractors are obtained,and thevarious bounds are dependent of the mesh sizes. 相似文献
38.
39.
40.
A multi-exposure of color fringes method has been developed to improve the capture speed of a conventional color CCD camera. In the method, four groups of projected fringe patterns encoded with different colors and different directions are stored in one CCD frame. Therefore the capture frequency of the conventional CCD can be improved to 200 Hz. It is available to measure the insect wings with low beating frequency, such as dragonfly, moth, or butterfly, whose beating frequency is about 30–40 Hz. We have used the method to measure the beating motion of a moth successfully. 相似文献