全文获取类型
收费全文 | 26111篇 |
免费 | 2260篇 |
国内免费 | 1108篇 |
专业分类
电工技术 | 517篇 |
技术理论 | 5篇 |
综合类 | 1754篇 |
化学工业 | 11317篇 |
金属工艺 | 1444篇 |
机械仪表 | 576篇 |
建筑科学 | 1172篇 |
矿业工程 | 610篇 |
能源动力 | 792篇 |
轻工业 | 3436篇 |
水利工程 | 336篇 |
石油天然气 | 1242篇 |
武器工业 | 148篇 |
无线电 | 1434篇 |
一般工业技术 | 2843篇 |
冶金工业 | 926篇 |
原子能技术 | 302篇 |
自动化技术 | 625篇 |
出版年
2024年 | 102篇 |
2023年 | 368篇 |
2022年 | 637篇 |
2021年 | 811篇 |
2020年 | 834篇 |
2019年 | 757篇 |
2018年 | 692篇 |
2017年 | 776篇 |
2016年 | 864篇 |
2015年 | 887篇 |
2014年 | 1509篇 |
2013年 | 1474篇 |
2012年 | 1919篇 |
2011年 | 1858篇 |
2010年 | 1391篇 |
2009年 | 1425篇 |
2008年 | 1146篇 |
2007年 | 1599篇 |
2006年 | 1465篇 |
2005年 | 1297篇 |
2004年 | 1146篇 |
2003年 | 1008篇 |
2002年 | 860篇 |
2001年 | 729篇 |
2000年 | 679篇 |
1999年 | 514篇 |
1998年 | 439篇 |
1997年 | 388篇 |
1996年 | 357篇 |
1995年 | 285篇 |
1994年 | 229篇 |
1993年 | 174篇 |
1992年 | 169篇 |
1991年 | 112篇 |
1990年 | 100篇 |
1989年 | 75篇 |
1988年 | 44篇 |
1987年 | 49篇 |
1986年 | 47篇 |
1985年 | 50篇 |
1984年 | 44篇 |
1983年 | 31篇 |
1982年 | 63篇 |
1981年 | 15篇 |
1980年 | 16篇 |
1978年 | 5篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1975年 | 8篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
111.
Lucia RussoErasmo Mancusi Pier Luca MaffettoneSilvestro Crescitelli 《Chemical engineering science》2002,57(24):5065-5082
In this work, we discuss how periodic forcing may induce symmetry properties into mathematical models of chemical reactors. We define a class of reactors subjected to discontinuous periodic forcing, and show that all the reactors belonging to this class have spatio-temporal symmetry. This symmetry and its influence on the possible bifurcation scenarios are discussed. The bifurcation analysis is carried out with suitable discrete systems that exploit a property of the Poincaré map. In fact, it is shown that the spatio-temporal symmetry induced by the forcing makes the Poincaré map of the continuous system an iterate of another map. On this basis, a technique to implement parameter continuation methods is proposed. With such a technique, it is also possible to characterize symmetric and nonsymmetric regimes and unstable limit sets otherwise undetected with “bruteforce” approaches. Examples for reverseflow reactors and networks of n-reactors with periodically switched feed and discharge positions are presented. 相似文献
112.
R. Niebuhr K. H. Bachem U. Kaufmann M. Maier C. Merz B. Santic P. Schlotter H. Jürgensen 《Journal of Electronic Materials》1997,26(10):1127-1130
Oxygen doped GaN has been grown by metalorganic chemical vapor deposition using N2O as oxygen dopant source. The layers were deposited on 2″ sapphire substrates from trimethylgallium and especially dried
ammonia using nitrogen (N2) as carrier gas. Prior to the growth of the films, an AIN nucleation layer with a thickness of about 300? was grown using
trimethylaluminum. The films were deposited at 1085°C at a growth rate of 1.0 μm/h and showed a specular, mirrorlike surface.
Not intentionally doped layers have high resistivity (>20 kW/square). The gas phase concentration of the N2O was varied between 25 and 400 ppm with respect to the total gas volume. The doped layers were n-type with carrier concentrations
in the range of 4×1016 cm−3 to 4×1018 cm−3 as measured by Hall effect. The observed carrier concentration increased with increasing N2O concentration. Low temperature photoluminescence experiments performed on the doped layers revealed besides free A and B
exciton emission an exciton bound to a shallow donor. With increasing N2O concentration in the gas phase, the intensity of the donor bound exciton increased relative to that of the free excitons.
These observations indicate that oxygen behaves as a shallow donor in GaN. This interpretation is supported by covalent radius
and electronegativity arguments. 相似文献
113.
湖南省江垭大坝10号坝段由于温度变化影响及该坝段坝型狭高,出现了两条内裂缝和不密实混凝土所构成的渗水通道.经过前期勘探后,在采取了有效的安全监测措施下,运用了化学灌浆和超细水泥灌浆进行了加固处理,灌区混凝土体疏松区与裂缝得到了有效充填,混凝土体完整性得到了很大改善,经压水试验检查完全满足预期要求,达到了加固处理的目的. 相似文献
114.
光学活性物质的工业生产方法 总被引:2,自引:0,他引:2
本文介绍了光学8活性牺牲垢几种工业规模的生产方法及最新的进展,分析了各种方法的特点及存在的问题。 相似文献
115.
116.
117.
An FTIR experiment especially designed to study the growth of an organosilane layer at the interface between a solution and a flat silica surface is presented. High sensitivity is achieved by using the attenuated total reflection (ATR) technique in a liquid flow cell. The ATR crystal, either silicon or germanium, is covered with a very thin silica layer. Chemical reactions of a mono-and a di-hydrolyzable silane with the silica substrate have been investigated. The grafting of a submonolayer of the first reagent has been monitored by following the C-H and SiO-H vibrations. The density of grafted molecules has been estimated and information on the nature of the chemical bonding has been achieved. Evidence for the chain-polymerization of the dihydrolyzable silane at the substrate/solution interface has been inferred from the appearance of a Si-O-Si absorption band. 相似文献
118.
H. Ebe T. Okamoto H. Nishino T. Saito Y. Nishijima M. Uchikoshi M. Nagashima H. Wada 《Journal of Electronic Materials》1996,25(8):1358-1361
CdTe epilayers were grown directly on (100), (211), and (111) silicon substrates by metalorganic chemical vapor deposition
(MOCVD). The crystallinity and the growth orientation of the CdTe film were dependent on the surface treatment of the Si substrate.
The surface treatment consisted of exposure of the Si surface to diethyltelluride (DETe) at temperatures over 600°C prior
to CdTe growth. Direct growth of CdTe on (100) Si produced polycrystalline films whereas (lll)B single crystals grew when
Si was exposed to DETe prior to CdTe growth. On (211) Si, single crystal films with (133)A orientation was obtained when grown
directly; but produced films with (211)A orientation when the Si surface was exposed to DETe. On the other hand, only (lll)A
CdTe films were possible on (111) Si, both with and without Te source exposure, although twinning was increased after exposure.
The results indicate that the exposure to a Te-source changes the initial growth stage significantly, except for the growth
on (111) Si. We propose a model in which a Te atom replaces a Si atom that is bound to two Si atoms. 相似文献
119.
对断裂的联接环进行了化学成分、机械性能、显微组织核验,指出回火工艺不当、锻造缺陷以及原材料化学成分不合格,是造成断裂事故的主要原因.在此基础上.提出了改进措施. 相似文献
120.