全文获取类型
收费全文 | 6383篇 |
免费 | 1281篇 |
国内免费 | 536篇 |
专业分类
化学 | 3064篇 |
晶体学 | 345篇 |
力学 | 538篇 |
综合类 | 47篇 |
数学 | 468篇 |
物理学 | 3738篇 |
出版年
2024年 | 9篇 |
2023年 | 50篇 |
2022年 | 147篇 |
2021年 | 206篇 |
2020年 | 252篇 |
2019年 | 207篇 |
2018年 | 170篇 |
2017年 | 200篇 |
2016年 | 305篇 |
2015年 | 261篇 |
2014年 | 314篇 |
2013年 | 490篇 |
2012年 | 365篇 |
2011年 | 483篇 |
2010年 | 400篇 |
2009年 | 397篇 |
2008年 | 414篇 |
2007年 | 456篇 |
2006年 | 406篇 |
2005年 | 344篇 |
2004年 | 318篇 |
2003年 | 285篇 |
2002年 | 219篇 |
2001年 | 194篇 |
2000年 | 163篇 |
1999年 | 138篇 |
1998年 | 141篇 |
1997年 | 102篇 |
1996年 | 99篇 |
1995年 | 80篇 |
1994年 | 86篇 |
1993年 | 73篇 |
1992年 | 69篇 |
1991年 | 44篇 |
1990年 | 51篇 |
1989年 | 42篇 |
1988年 | 34篇 |
1987年 | 32篇 |
1986年 | 21篇 |
1985年 | 28篇 |
1984年 | 15篇 |
1982年 | 13篇 |
1981年 | 7篇 |
1980年 | 10篇 |
1979年 | 16篇 |
1978年 | 9篇 |
1974年 | 4篇 |
1973年 | 8篇 |
1971年 | 4篇 |
1970年 | 4篇 |
排序方式: 共有8200条查询结果,搜索用时 203 毫秒
971.
972.
973.
采用无模板化学气相沉积法,以二茂铁为催化剂,二甲苯为碳源,利用单温炉加热装置制备了定向碳纳米管阵列。运用扫描电子显微镜、透射电子显微镜、拉曼光谱和X射线衍射仪等对定向碳纳米管阵列的形貌、成分和物相进行细致的分析和表征。结果表明:制得的碳纳米管阵列具有良好的定向性和多壁管状结构,并且石墨化程度高;碳纳米管中除碳元素外,管中包含有少量以纳米颗粒和纳米线形式存在的铁及其化合物,主要成分是铁和碳化铁。结合碳纳米管的制备和透射电子显微镜分析表征结果,认为超长碳纳米管阵列的生长模式为底部生长方式,即经历催化剂分解、催化、成核、长大、中毒、凝聚成粒和连接成线的循环过程,正是由于碳源和催化剂的连续供应促成了碳纳米管阵列的快速定向生长。 相似文献
974.
Nicholas Kasch 《Liquid Crystals Today》2013,22(3):70-71
Liquid crystals (LCs) are mesogenic phases of matter which combine liquid fluidity with crystalline solid properties. Precise knowledge of the molecular orientations – close to the boundaries and within the material bulk – is necessary for understanding their flow behaviour, especially in microfluidic settings. While the boundary conditions are set, passively, by surface-induced molecular orientations, the bulk orientation in flow is determined, actively, by the anisotropic coupling between the flow and the molecular orientation. Together, the surface and the bulk orientations offer a range of topological constraints within microfluidic channels, which affect the evolution and sustenance of flow-induced phenomena in LC-based systems. The concept of topological microfluidics can be extended to different classes of anisotropic fluids, allowing us to explore and to employ such fluids as complex functional materials for microfluidics, thereby significantly broadening the reach of conventional microfluidics. 相似文献
975.
J. Molenda I. Nowak L. Jedynak J. Marzec A. Stokłosa 《Molecular Crystals and Liquid Crystals》2013,570(2):199-204
Abstract Electrical conductivity and thermoelectric power measurements (77–300K) of both the pure and electrochemically doped with lithium Bi2Sr2CaCu2O8 system, are presented. Clear correlation between transport and electrochemical properties of LixBi2Sr2CaCu2O8 was shown. 相似文献
976.
Dmitry E. Sklovsky Vera A. Nalimova John E. Fischer 《Molecular Crystals and Liquid Crystals》2013,570(1):763-768
Abstract We report in situ measurements of four-probe de resistance (R) of K-doped purified single wall carbon nanotube (SWNT) “buckypaper” as a function of quasi-hydrostatic pressure. Doped samples show completely different behavior compared to that of pristine nanotubes in the pressure range up to 90 kbar. The characteristic increase in the resistance of pristine buckypaper above 10 kbar, associated with the formation of kinks or/and twists of tubes, is not observed in K-doped samples. This may originate from 1) a substantial change in electronic band structure of donor intercalated nanotubes, 2) completely different transport properties of defect structures, or 3) higher stiffness of doped SWNT's which prevents formation of kinks and twists in this pressure range. On deintercalation, the pristine behavior of R(P) is restored, establishing the reversibility of potassium vapor-transport doping. 相似文献
977.
Oxides have become a key ingredient for new concepts of electronic devices. To a large extent, this is due to the profusion of new physics and novel functionalities arising from ultrathin oxide films and at oxide interfaces. We present here a perspective on selected topics within this vast field and focus on two main issues. The first part of this review is dedicated to the use of ultrathin films of insulating oxides as barriers for tunnel junctions. In addition to dielectric non-magnetic epitaxial barriers, which can produce tunneling magnetoresistances in excess of a few hundred percent, we pay special attention to the possibility of exploiting the multifunctional character of some oxides in order to realize ‘active’ tunnel barriers. In these, the conductance across the barrier is not only controlled by the bias voltage and/or the electrodes magnetic state, but also depends on the barrier ferroic state. Some examples include spin-filtering effects using ferro- and ferrimagnetic oxides, and the possibility of realizing hysteretic, multi-state junctions using ferroelectric barriers. The second part of this review is devoted to novel states appearing at oxide interfaces. Often completely different from those of the corresponding bulk materials, they bring about novel functionalities to be exploited in spintronics and electronics architectures. We review the main mechanisms responsible for these new properties (such as magnetic coupling, charge transfer and proximity effects) and summarize some of the most paradigmatic phenomena. These include the formation of high-mobility two-dimensional electron gases at the interface between insulators, the emergence of superconductivity (or ferromagnetism) at the interface between non-superconducting (or non-ferromagnetic) materials, the observation of magnetoelectric effects at magnetic/ferroelectric interfaces or the effects of the interplay and competing interactions at all-oxide ferromagnetic/superconducting interfaces. Finally, we link up the two reviewed research fields and emphasize that the tunneling geometry is particularly suited to probe novel interface effects at oxide barrier/electrode interfaces. We close by giving some directions toward tunneling devices exploiting novel oxide interfacial phenomena. 相似文献
978.
Yaqi Yan Zhenkun Wu Jinhai Si Lihe Yan Yiqi Zhang Chenzhi Yuan Jia Sun Yanpeng Zhang 《Annals of Physics》2013
We theoretically deduce the macroscopic symmetry constraints for arbitrary odd-order nonlinear susceptibilities in homogeneous media including atomic vapors for the first time. After theoretically calculating the expressions using a semiclassical method, we demonstrate that the expressions for third- and fifth-order nonlinear susceptibilities for undressed and dressed four- and six-wave mixing (FWM and SWM) in atomic vapors satisfy the macroscopic symmetry constraints. We experimentally demonstrate consistence between the macroscopic symmetry constraints and the semiclassical expressions for atomic vapors by observing polarization control of FWM and SWM processes. The experimental results are in reasonable agreement with our theoretical calculations. 相似文献
979.
We study the effect of external potential on transport properties of the fermionic two-leg ladder model. The response of the system to a local perturbation is strongly dependent on the ground state properties of the system and especially on the dominant correlations. We categorize all phases and transitions in the model (for incommensurate filling) and introduce “hopping-driven transitions” that the system undergoes as the inter-chain hopping is increased from zero. We also describe the response of the system to an ionic potential. The physics of this effect is similar to that of the single impurity, except that the ionic potential can affect the bulk properties of the system and in particular induce true long range order. 相似文献
980.
Single-crystal Eu3+-doped wurtzite ZnO micro- and nanowires were synthesized by chemical vapor deposition. The nanostructures grew via a self-catalytic mechanism on the walls of an alumina boat. The structure and properties of the doped ZnO were characterized using X-ray diffraction, energy-dispersive X-ray spectroscopy, scanning and transmission electron microscopy, and photoluminescence (PL) methods. A 10-min synthesis yielded vertically grown nanowires of 50–400 nm in diameter and several micrometers long. The nanowires grew along the ±[0001] direction. The Eu3+ concentration in the nanowires was 0.8 at.%. The crystal structure and microstructure of were compared for Eu3+-doped and undoped ZnO. PL spectra showed a red shift in emission for Eu3+-doped (2.02 eV) compared to undoped ZnO nanowires (2.37 eV) due to Eu3+ intraionic transitions. Diffuse reflectance spectra revealed widening of the optical bandgap by 0.12 eV for Eu3+-doped compared to undoped ZnO to yield a value of 3.31 eV. Fourier-transform infrared spectra confirmed the presence of europium in the ZnO nanowires. 相似文献