全文获取类型
收费全文 | 1837篇 |
免费 | 416篇 |
国内免费 | 172篇 |
专业分类
化学 | 433篇 |
晶体学 | 4篇 |
力学 | 104篇 |
综合类 | 29篇 |
数学 | 54篇 |
物理学 | 545篇 |
无线电 | 1256篇 |
出版年
2024年 | 52篇 |
2023年 | 153篇 |
2022年 | 336篇 |
2021年 | 307篇 |
2020年 | 260篇 |
2019年 | 152篇 |
2018年 | 105篇 |
2017年 | 91篇 |
2016年 | 72篇 |
2015年 | 55篇 |
2014年 | 57篇 |
2013年 | 70篇 |
2012年 | 53篇 |
2011年 | 40篇 |
2010年 | 54篇 |
2009年 | 51篇 |
2008年 | 43篇 |
2007年 | 45篇 |
2006年 | 41篇 |
2005年 | 51篇 |
2004年 | 38篇 |
2003年 | 39篇 |
2002年 | 28篇 |
2001年 | 36篇 |
2000年 | 42篇 |
1999年 | 21篇 |
1998年 | 11篇 |
1997年 | 12篇 |
1996年 | 13篇 |
1995年 | 15篇 |
1994年 | 9篇 |
1993年 | 8篇 |
1992年 | 8篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 2篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1971年 | 1篇 |
1959年 | 2篇 |
排序方式: 共有2425条查询结果,搜索用时 15 毫秒
1.
Numerical simulation, using SILVACO-TCAD, is carried out to explain experimentally observed effects of different types of deep levels on the capacitance–voltage characteristics of p-type Si-doped GaAs Schottky diodes grown on high index GaAs substrates. Two diodes were grown on (311)A and (211)A oriented GaAs substrates using Molecular Beam Epitaxy (MBE). Although, deep levels were observed in both structures, the measured capacitance–voltage characteristics show a negative differential capacitance (NDC) for the (311)A diodes, while the (211)A devices display a usual behaviour. The NDC is related to the nature and spatial distribution of the deep levels, which are characterized by the Deep Level Transient Spectroscopy (DLTS) technique. In the (311)A structure only majority deep levels (hole traps) were observed while both majority and minority deep levels were present in the (211)A diodes. The simulation, which calculates the capacitance–voltage characteristics in the absence and presence of different types of deep levels, agrees well with the experimentally observed behaviour. 相似文献
2.
3.
通过比较各种软件无线电结构的优缺点,针对既具有交换网络结构又具有分层结构优点的基于交换网络的分层无线电结构方案,提出了部分改进思想。 相似文献
4.
Shufeng Zuo 《Applied Surface Science》2006,253(5):2508-2514
Al-pillared clays supported rare earths (RE/Al-PILC) are prepared and used as supports of palladium catalysts for deep oxidation of low concentrations of benzene (130-160 ppm). The supports and catalysts are characterized by X-ray powder diffraction (XRD), FT-IR, BET, transmission electron microscopy (TEM) and temperature-programmed reduction (H2-TPR). The results show that Al-pillaring results in a strong increase in the basal spacing (d0 0 1) from about 1.2 to 1.8 nm, and an increase in the BET surface area from 63.6 (±3.2) to 238.8 (±11.9) m2/g. Activity tests of deep oxidation of low concentration benzene show catalysts supported on Al-PILC and RE/Al-PILC are obviously more active than that on raw clay. Pd/6% Ce/Al-PILC, in particular, can catalyze the complete oxidation of low concentration benzene at a temperature as low as about 290 °C. 相似文献
5.
光刻胶灰化工艺与深亚微米线条的制作 总被引:5,自引:1,他引:4
随着器件尺寸的缩小,细线条的制作成为很关键的工艺,普通光学光刻已接近其分辨率的极限,而电子束光刻和X射线光刻技术复杂、费用昂贵。本文对光刻胶灰化工艺进行了分析和研究,并应用此工艺进行了深亚微米线条的制作,在普通光学光刻机上制作出宽度小于0.25μm细线条。我们已将此工艺成功地应用在深亚微米MOSFET的制作中。 相似文献
6.
将DLTS用于对InAs/GaAsQD结构样品的测量,测定了QD能级发射载流子的热激活能;获得了QD能级俘获电子过程伴随有多声子发射(MPE)、QD能级存在一定程度的展宽、以及在某些特定的生长条件下,存在亚稳生长构形的实验证据.结果表明:DLTS在QD体系的研究中有其特有的功能 相似文献
7.
完成了19F+27Al深部非弹性碰撞产物的角分布测量.初步分析了反应产B,C,N,O,F,Ne,Na,Mg和Al的实验室系角分布,展现出深部非弹性反应机制的特点,显示了反应系统随时间的演化过程. Angular distributions of fragments produced in the deep inelastic collision of~(19)F+~(27)Al have been measured for incident energy of 114 MeV at θ_(lab)= 9~(o), 24~(o), 40~(o), 55~(o), 70~(o) and 85~(o). Angular distributions of dissipative products B, C, N, O, F, Ne, Na, Mg and Al are analyzed to provide an evolution process of the intermediate dinuclear system formed in the reaction. 相似文献
8.
Makoto Kasu Rangaiya Rao Susumu Noda Akio Sasaki 《Journal of Electronic Materials》1991,20(9):691-693
Properties of theDX centers in Al0.5Ga0.5As bulk alloy (b-AL), (AlAs)2 (GaSa)2 ordered superlattice (o-SL) and (AlAs)
m
(GaAs)
n
disordered superlattice (d-SL) (m = 1, 2, 3,n = 1, 2, 3) with the same macroscopic composition were measured and compared. By deconvolution of deep level transient spectroscopy
(DLTS) spectrum due to theDX center, we have found a decrease in the number of separate peaks in DLTS spectrum in an intentionally atomic ordered arrangement.
Visiting Scholar of the Japan Society for the Promotion of Science. On leave from Department of Electrical Engineering, San
Jose State University, San Jose, California 95192-0084, USA. 相似文献
9.
A rigorous formulation of capacitance changes during trap filling processes is presented and used to accurately determine
the electron capture cross section of EL2 in GaAs at a particular temperature, 377K, in this case. The value, σn (377K) = 2.7 × 10−16 cm2, is compared with that predicted from the emission dependence. 相似文献
10.
The thermal properties of -lactoglobulin (-LG) were studied by differential scanning calorimetry (DSC) under different medium conditions.pH, neutral salts, protein perturbants, and polyols all affected the DSC characteristics of -LG. Acylation with fatty acids also changed the thermal properties, particularly peak width at half-height. The results suggest that the structural stability of -LG is controlled by non-covalent forces, particularly electrostatic and hydrophobic interactions. Disulfide bonds did not contribute to the thermal response of -LG. Fatty N-acyl-amino acids caused marked increases in thermal stability and decreases in denaturation enthalpy, and additional peaks were observed in the presence of some palmitoyl derivatives.Contribution No. 2310, Centre for Food and Animal Research.We thank D. Raymond for her excellent technical assistance. 相似文献