全文获取类型
收费全文 | 713篇 |
免费 | 72篇 |
国内免费 | 15篇 |
专业分类
化学 | 573篇 |
晶体学 | 2篇 |
力学 | 25篇 |
综合类 | 1篇 |
数学 | 36篇 |
物理学 | 163篇 |
出版年
2024年 | 1篇 |
2023年 | 12篇 |
2022年 | 45篇 |
2021年 | 35篇 |
2020年 | 47篇 |
2019年 | 39篇 |
2018年 | 18篇 |
2017年 | 34篇 |
2016年 | 31篇 |
2015年 | 35篇 |
2014年 | 36篇 |
2013年 | 48篇 |
2012年 | 38篇 |
2011年 | 50篇 |
2010年 | 29篇 |
2009年 | 50篇 |
2008年 | 42篇 |
2007年 | 40篇 |
2006年 | 33篇 |
2005年 | 22篇 |
2004年 | 19篇 |
2003年 | 16篇 |
2002年 | 10篇 |
2001年 | 4篇 |
2000年 | 9篇 |
1999年 | 4篇 |
1998年 | 5篇 |
1997年 | 2篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 7篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1976年 | 1篇 |
1973年 | 2篇 |
排序方式: 共有800条查询结果,搜索用时 15 毫秒
751.
La2Zr2O7 (LZO) layers have been recently investigated as potential buffer layers for superconducting YBa2Cu3O7–x coated conductors deposited on Ni tapes. Chemical solution deposition was used for LZO layer preparation. X-ray photoelectron
spectroscopy (XPS) depth profiling is demonstrated to be an important method for layer characterization in addition to X-ray
diffraction techniques. XPS measurements revealed layers that are homogeneous in depth, very smooth, and have no significant
impurities. A slight difference to the nominal La:Zr stoichimetry is discussed in combination with structural defects that
are suspected from spectral changes during ion sputtering. 相似文献
752.
Morphological similarity of road networks and cracks 总被引:1,自引:0,他引:1
An investigation was made regarding to what extent road network patterns are reproduced by a crack model from a viewpoint that they seem to resemble crack patterns in morphology. A desiccation model using double-layered cellular meshes was considered with the parameters representing the anisotropy of the material and the coarseness of grains, together with the introduction of singularities in points and in lines. The model can generally reproduce the real crack patterns and the road network patterns of cities with characteristic morphology by appropriately choosing the values of parameters, indicating that the similar mechanism acts on the formation of road networks and cracks of material although the relevant scales of space time differ from each other. Factors which make the road networks more complex and irregular in morphology were also investigated. 相似文献
753.
754.
755.
New electrolyte systems for profiling n-type indium phosphide (InP) have been reported and are compared with the conventional
HCl electrolyte. Among the new electrolytes, the electrolyte comprising HNO3-HF-H2O has better characteristics and is best suited for profiling InP material. Both epitaxial layers and substrate materials
have been subjected to electrochemical carrier concentration profiling using the new electrolyte and the estimated concentration
values are compared with that of Hall effect measurements. Barrier heights of the new electrolytes have been calculated. For
the first time, the dopant profiling of a complete device structure grown by the chemical beam epitaxy technique for the realization
of laser and semiconductor optical amplifier structures has been presented.
Received: 1 February 1999 / Accepted: 1 April 1999 相似文献
756.
A complex poly(vinylidene difluoride) (PVdF)/poly(methyl methacrylate) (PMMA)‐based coil coating formulation has been investigated using time‐of‐flight SIMS (ToF‐SIMS). Employing a Bi3+ analysis source and a Buckminsterfullerene (C60) sputter source, depth profiles were obtained through the polymeric materials in the outer few nanometres of the PVdF topcoat. These investigations demonstrate that the PVdF coating's air/coating interface is composed principally of the flow agent included in the formulation. Elemental depth profiles obtained in the negative ion mode demonstrate variations in the carbon, oxygen and fluorine concentrations within the coating with respect to depth. All three elemental depth profiles suggest that the PVdF coating bulk possesses a constant material composition. The oxygen depth profile reveals the presence of a very thin oxygen‐rich sub‐surface layer in the PVdF coating, observed within the first second of the sputter/etch profile. Retrospectively, extracted mass spectra (from the elemental depth profile raw data set) of the PVdF coating sub‐surface and bulk layers indicates this oxygen‐rich sub‐surface layer results from segregation of the acrylic co‐polymers in the formulation towards the PVdF coating air/coating interface. Molecular depth profiles obtained in both the positive and negative secondary ion modes provide supporting evidence to that of the elemental depth profiles. The molecular depth profiles confirm the presence of a sub‐surface layer rich in the acrylic co‐polymers indicating segregation of the co‐polymers towards the PVdF topcoats air‐coating surface. The molecular depth profiles also confirm that the PVdF component of the topcoat is distributed throughout the coating but is present at a lower concentration at the air‐coating interface and in the sub‐surface regions of the coating, than in the coating bulk. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
757.
758.
In this paper, we consider a unified framework of multiclass multicriteria mixed equilibrium, and the existence of uniform link tolls supporting such a mixed equilibrium as a system optimum. The network users are divided into different classes, and each class of traveler perceives his/her disutility associated with a route as a combination of two criteria given, respectively, by the travel time disutility and the time-irrelevant travel disutility. And users in a common class follow either user equilibrium (UE) principle or Cournot–Nash (CN) principle. A variational inequality model characterizing the multiclass multicriteria UE–CN mixed equilibrium behavior is developed. By utilizing the dual theory, we establish the existence of uniform link tolls supporting such mixed equilibrium as a system optimum. 相似文献
759.
The main active components of present-day car catalysts are the noble metals Pt, Pd and Rh, belonging to the platinum group elements (PGEs). It is recognized that these elements are being spread into the environment to an as-yet incompletely known extent, mainly due to surface abrasion of the catalyst during car operation. These new pollutants have motivated extensive research on PGE determination. Our work is planned to ascertain the health and ecosystem risks of these PGEs emitted through a series of interrelated objectives that address the pathway of these elements from the catalyst to the different environmental compartments. Combined studies of catalyst surface abrasion and exhaust fumes analysis, the monitoring of Pt, Pd and Rh in airborne particles and road dust sediments and bioaccumulation studies in aquatic organisms, plants and urine enable a realistic assessment of the risk that this release represents for man and environment. In this work some previous results are presented. 相似文献
760.
An I2/CuI-promoted multi-component reaction from pyridines, aryl methyl ketones and electron deficient acrylates has been accomplished in a “one-pot” manner, which provides a straightforward and efficient access to C-3 acylated indolizines. The key intermediate of N-ylides is hypothesized to be generated in situ from pyridines and (hetero)aryl methyl ketones in the presence of iodine. This method has been applied in the synthesis of two molecules with anticonvulsant and anti-inflammatory activities. 相似文献