全文获取类型
收费全文 | 18923篇 |
免费 | 941篇 |
国内免费 | 140篇 |
专业分类
电工技术 | 330篇 |
综合类 | 32篇 |
化学工业 | 4204篇 |
金属工艺 | 592篇 |
机械仪表 | 629篇 |
建筑科学 | 371篇 |
矿业工程 | 47篇 |
能源动力 | 1367篇 |
轻工业 | 1158篇 |
水利工程 | 151篇 |
石油天然气 | 84篇 |
武器工业 | 1篇 |
无线电 | 2356篇 |
一般工业技术 | 4313篇 |
冶金工业 | 1441篇 |
原子能技术 | 172篇 |
自动化技术 | 2756篇 |
出版年
2024年 | 101篇 |
2023年 | 420篇 |
2022年 | 995篇 |
2021年 | 1156篇 |
2020年 | 906篇 |
2019年 | 937篇 |
2018年 | 1222篇 |
2017年 | 956篇 |
2016年 | 927篇 |
2015年 | 601篇 |
2014年 | 838篇 |
2013年 | 1505篇 |
2012年 | 888篇 |
2011年 | 1067篇 |
2010年 | 857篇 |
2009年 | 805篇 |
2008年 | 709篇 |
2007年 | 567篇 |
2006年 | 469篇 |
2005年 | 359篇 |
2004年 | 272篇 |
2003年 | 240篇 |
2002年 | 187篇 |
2001年 | 177篇 |
2000年 | 169篇 |
1999年 | 168篇 |
1998年 | 293篇 |
1997年 | 239篇 |
1996年 | 219篇 |
1995年 | 169篇 |
1994年 | 157篇 |
1993年 | 151篇 |
1992年 | 103篇 |
1991年 | 130篇 |
1990年 | 99篇 |
1989年 | 95篇 |
1988年 | 80篇 |
1987年 | 88篇 |
1986年 | 75篇 |
1985年 | 85篇 |
1984年 | 73篇 |
1983年 | 71篇 |
1982年 | 60篇 |
1981年 | 70篇 |
1980年 | 48篇 |
1979年 | 31篇 |
1978年 | 27篇 |
1977年 | 26篇 |
1976年 | 35篇 |
1971年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
S Kasiviswanathan P S Asoka Kumar B K Mathur K L Chopra 《Bulletin of Materials Science》1996,19(2):411-416
Surface structure of thin silver films (200 Å) on two technologically important films, indium tin oxide (ITO) and aluminium oxide, has been studied using scanning tunneling microscope. ITO films were prepared by reactive electron beam evaporation. Aluminium oxide films were prepared by oxidizing 2000 Å thick aluminium films evaporated on to H2 terminated single crystal silicon substrates. The surface structure of silver on ITO and aluminium oxide appeared to be same and was characteristic of Stranski-Krastanov type. The observed asymmetry in the island shape was attributed to the anisotropic nature of the strain fields surrounding the nucleation centres. 相似文献
112.
Erythrocyte ghosts were exposed to various levels of oxyradical shock in order to identify the extent of accumulation of peroxidative intermediates. Malondialdehyde reacting end products were the same in all different models. But, the accumulation of dienyl radical species increased with higher intensity of oxyradical shock. These dienyl radicals may rearrange to create a homogeneous smectic multilamellar microenvironment which may be more fluid in terms of the molecular dynamics. 相似文献
113.
114.
Summary The three-dimensional Poisson-Voronoi model, which is topologically equivalent to the microstructure of real ceramics and metals, has been used to study the stress distribution within a simulated polycrystalline aggregate having 200 grains. Micro-stresses such as the maximum principal stress, maximum shear stress, first invariant of stress, and Von-Mises stress are found to vary systematically with the anisotropy of single crystal. 相似文献
115.
J Barrette R Bellwied P Braun-Munzinger WE Cleland T Cormier G Dadusc G David J Dee O Dietzsch M Fatyga SV Greene JV Germani JR Hall TK Hemmick N Herrmann RW Hogue B Hong K Jayananda D Kraus BS Kumar R Lacasse D Lissauer WJ Llope TW Ludlam R Majka SK Mark JT Mitchell M Muthuswamy E O'Brien C Pruneau FS Rotondo da Silva NC J Simon-Gillo U Sonnadara J Stachel H Takai EM Takagui TG Throwe L Waters C Winter D Wolfe CL Woody N Xu Y Zhang Z Zhang C Zou 《Canadian Metallurgical Quarterly》1995,52(5):2679-2683
116.
The kinetics and mechanism of oligomerization of cardanol over acid catalysts were studied. GPC results showed the formation of a mixture of oligomers such as dimer, trimer, tetramer, etc. IR spectra of the products of oligomerization showed a decrease in the intensity of the double bond absorption band at 1630 cm?1 and the disappearance of terminal vinyl bands at 895 cm?1 and 907 cm?1. 1H NMR spectra showed drastic changes in the unsaturated proton resonance signals at 5.5δ with respect to saturated protons at 0.2–2.5δ. The ratio of resonance integrals of unsaturated to saturated protons decreased from 1 : 6.5 to 1 : 20 after oligomerization. GPC studies showed that the rate of formation of the dimer, trimer, tetramer, etc. follow an identical path and that the individual oligomers are formed in the same weight percentage at any time during the reaction. A kinetic scheme is proposed to explain this phenomenon. Kinetic studies showed that the oligomerization reaction follows first order kinetics with respect to the monomer concentration and the rate constant is K = 6.6 × 10?5s?1. A probable mechanism for the oligomerization of cardanol is proposed. 相似文献
117.
Xiang Lu S. Sundar Kumar Iyer Jin Lee Brian Doyle Zhineng Fan Paul K. Chu Chenming Hu Nathan W. Cheung 《Journal of Electronic Materials》1998,27(9):1059-1066
We have demonstrated feasibility to form silicon-on-insulator (SOI) substrates using plasma immersion ion implantation (PIII)
for both separation by implantation of oxygen and ion-cut. This high throughput technique can substantially lower the high
cost of SOI substrates due to the simpler implanter design as well as ease of maintenance. For separation by plasma implantation
of oxygen wafers, secondary ion mass spectrometry analysis and cross-sectional transmission electron micrographs show continuous
buried oxide formation under a single-crystal silicon overlayer with sharp Si/SiO2 interfaces after oxygen plasma implantation and high-temperature (1300°C) annealing. Ion-cut SOI wafer fabrication technique
is implemented for the first time using PIII. The hydrogen plasma can be optimized so that only one ion species is dominant
in concentration and there are minimal effects by other residual ions on the ion-cut process. The physical mechanism of hydrogen
induced silicon surface layer cleavage has been investigated. An ideal gas law model of the microcavity internal pressure
combined with a two-dimensional finite element fracture mechanics model is used to approximate the fracture driving force
which is sufficient to overcome the silicon fracture resistance. 相似文献
118.
B. S. Ashok Kumar William A. Klos Eric R. Taylor 《Electric Power Systems Research》1994,30(3):229-234
Recent research reports appear to indicate a real possibility that the low-frequency electromagnetic field produced by the power transmission and distribution network presents a health problem. A critical assessment of the available information is presented here. The state of knowledge, available evidence and conflicting reports indicate a definite need for interim action by the power industry. New direction for analytical research, possible interim avoidance measures, proper advice to clients and the public are discussed. Detailed mathematical modeling for the linear and nonlinear dynamics of DNA and the chromosome as a whole is suggested. 相似文献
119.
Current–Voltage (I–V) characteristics have been studied at various temperatures in vacuum evaporated thin films of a-Se85Te15−x
Pb
x
(x = 0, 2, 4, 6) alloys. These characteristics show that, at low electric fields, an ohmic behaviour is observed. However, at
high electric fields (E ∼ 104 V/cm), the current becomes superohmic. At high fields, in case of samples having 0 and 2 at% of Pb, the experimental data
fits well with the theory of space charge limited conduction (SCLC) in case of uniform distribution of localized states in
the mobility gap. Such type of behaviour is not observed at higher concentration of Pb in the present glassy system due to
high conductivity. In these samples, joule heating due to large currents may prohibit the measurement of SCLC. Using the theory
of SCLC for the uniform distribution of the traps, the density of localized defect states near Fermi level is calculated for
these compositions. The results indicate that the density of defect states near Fermi level increases on addition of Pb to
binary Se85Te15alloy. This is explained in terms of electronegativity of Pb as compared to host elements. 相似文献
120.
Mani Azimi Ching-Tsun Chou Akhilesh Kumar Victor W. Lee Phamndra K. Mannava Seungjoon Park 《Formal Methods in System Design》2003,22(2):109-116
In the last three years or so we at Enterprise Platforms Group at Intel Corporation have been applying formal methods to various problems that arose during the process of defining platform architectures for Intel's processor families. In this paper we give an overview of some of the problems we have worked on, the results we have obtained, and the lessons we have learned. The last topic is addressed mainly from the perspective of platform architects. 相似文献