全文获取类型
收费全文 | 6389篇 |
免费 | 1163篇 |
国内免费 | 1054篇 |
专业分类
化学 | 3275篇 |
晶体学 | 35篇 |
力学 | 475篇 |
综合类 | 73篇 |
数学 | 1013篇 |
物理学 | 3735篇 |
出版年
2024年 | 6篇 |
2023年 | 80篇 |
2022年 | 120篇 |
2021年 | 169篇 |
2020年 | 239篇 |
2019年 | 212篇 |
2018年 | 180篇 |
2017年 | 201篇 |
2016年 | 214篇 |
2015年 | 215篇 |
2014年 | 308篇 |
2013年 | 574篇 |
2012年 | 407篇 |
2011年 | 400篇 |
2010年 | 325篇 |
2009年 | 414篇 |
2008年 | 459篇 |
2007年 | 456篇 |
2006年 | 451篇 |
2005年 | 385篇 |
2004年 | 358篇 |
2003年 | 326篇 |
2002年 | 281篇 |
2001年 | 218篇 |
2000年 | 230篇 |
1999年 | 188篇 |
1998年 | 188篇 |
1997年 | 164篇 |
1996年 | 105篇 |
1995年 | 99篇 |
1994年 | 84篇 |
1993年 | 74篇 |
1992年 | 77篇 |
1991年 | 60篇 |
1990年 | 45篇 |
1989年 | 36篇 |
1988年 | 35篇 |
1987年 | 32篇 |
1986年 | 27篇 |
1985年 | 27篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1982年 | 25篇 |
1981年 | 20篇 |
1980年 | 16篇 |
1979年 | 11篇 |
1978年 | 12篇 |
1977年 | 11篇 |
1976年 | 7篇 |
1973年 | 4篇 |
排序方式: 共有8606条查询结果,搜索用时 296 毫秒
951.
Reducing the ICRH (ion cyclotron range frequency) antenna-plasma interaction is one of the key points for reaching very long tokamak discharges. One problem which limits such discharges, is the appearance of hot spots on the surface of the antenna: Radio Frequency (RF) sheaths modify the properties of the edge plasma by rectifying the RF potential along open magnetic field lines and can induce hot spots. This paper investigates the corrections to sheath potentials introduced by the interactions between adjacent flux tubes. Our theoretical study started from an oscillating double Langmuir probe model, in which a transverse influx of current was included. This model was confronted with 1D PIC simulations along a magnetic field line, and demonstrated that current exchanges can decrease mean potentials. A 2D electrostatic fluid code was then developed, which couples adjacent flux tubes in a poloidal cross section with collisional conductivity or polarization currents. It showed that transverse currents are able to smooth structures smaller than a characteristic size in the sheath potential maps (results for Tore Supra). These computed rectified potentials can be used to obtain the DC electric fields in front of the antenna. And then, it gives an estimate of the particle drift and the energy flux on the antenna structure, which can explain hot spots. 相似文献
952.
953.
在相对论有效原子实势(RECP)近似下,用密度泛函(B3LYP/LANL2DZ)方法,优化计算PdYn,Pd2Yn(n=1~4)团簇的结构、光谱性质和能级分布.结果表明,团簇基态的HOMO 能级和LUMO能级均为负值,团簇易得电子,团簇的能隙(HLG)小,化学活性较强. 相似文献
954.
955.
采用密度泛函DFT中的B3LYP方法,选择LANL2DZ双ζ基组,优化并得到了Yn=(n=2—8)小团簇的基态平衡结构,同时计算出其电离势.结果表明,钇原子之间形成团簇最稳定的结构是倾向于平均配位数最大,其电离势没有“奇-偶”振荡或“幻数”效应,表明Yn团簇光致电离开始主要发生在Y原子局域化的4d轨道上的电子而不是在5s上.对Tomasz提出的钇团簇电离势的解析式进行合理地修正,修正后电离势解析式的计算值与实验值更接近.
关键词:
Y团簇
密度泛函
平衡几何结构
电离势 相似文献
956.
957.
958.
We present a model of a new paramagnetic defect center which results from the interaction of atomic hydrogen with the MgO(1 0 0) surface. DFT calculations have been performed using periodic supercells and embedded cluster models where long-range polarization effects are included explicitly. The H atom promotes the creation of an oxygen vacancy (F center) by formation of the FS+(OH−) defect where an hydroxyl group is adsorbed near an electron trapped in an oxygen vacancy. This new center has some characteristics similar to those of the classical FS+ centers but a smaller formation energy; furthermore, being globally neutral, it can be treated also with supercell methods. 相似文献
959.
T. G. G. Maffeïs G. T. Owen C. Malag G. Martinelli M. K. Kennedy F. E. Kruis S. P. Wilks 《Surface science》2004,550(1-3):21-25
In this work, we report a scanning tunnelling spectroscopy (STS) study of 30 and 10 nm tin dioxide nanoparticles. The STS spectra give a surface band gap of 2.5 eV for both samples and show that the density of surface states in the band gap is around 6 times higher for the 30 nm particles than for the 10 nm particles. This provides direct experimental evidence for our theoretical model, which predicts a decrease in the surface state density as the particle size decreases, and partly accounts for the improved sensitivity of gas sensing devices fabricated with nanoparticles. 相似文献
960.
Simona Percec Ross Getty Will Marshall Gabriel Skidd Roger French 《Journal of polymer science. Part A, Polymer chemistry》2004,42(3):541-550
Oligomers consisting of aromatic building blocks separated by alkynyl units were synthesized by Sonogashira cross-coupling of aryl halides with terminal acetylenes. Strong electron acceptors such as F and CF3 and weak electron donors like CH3 were placed as substituents on one of the benzene rings. Acetyl-protected sulfhydryl groups were attached to one end of these molecules to promote their self-organization on gold surfaces. The electron-transport properties of such self-assembled monolayers (SAMs) are highly sensitive to the local order of the molecules in the solid state. Single crystals were analyzed by X-ray diffraction experiments that revealed structural details that could lead to a better understanding of the electron-transport properties. The unsymmetrical substitution of the aromatic rings by electron-active groups in the ortho-, meta-, or para positions resulted in changes of such molecular parameters as bonding and torsion angles and planarity. These parameters, in turn, can affect the angle of the molecular attachment to a gold substrate and the density of the resulting SAMs. Patterned SAMs of some of these molecules and comparison alkane thiols were obtained on gold by microcontact printing or flooding. The SAM thickness was determined by spectroscopic ellipsometry. Surface potential differences between adjacent SAMs or between SAMs and the gold substrate were measured by scanning surface potential microscopy under ambient conditions. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 541–550, 2004 相似文献