全文获取类型
收费全文 | 96078篇 |
免费 | 1544篇 |
国内免费 | 452篇 |
专业分类
电工技术 | 901篇 |
综合类 | 2338篇 |
化学工业 | 13773篇 |
金属工艺 | 4981篇 |
机械仪表 | 3235篇 |
建筑科学 | 2996篇 |
矿业工程 | 608篇 |
能源动力 | 1445篇 |
轻工业 | 4584篇 |
水利工程 | 1420篇 |
石油天然气 | 392篇 |
武器工业 | 1篇 |
无线电 | 10083篇 |
一般工业技术 | 18536篇 |
冶金工业 | 5167篇 |
原子能技术 | 311篇 |
自动化技术 | 27303篇 |
出版年
2023年 | 70篇 |
2022年 | 141篇 |
2021年 | 233篇 |
2020年 | 169篇 |
2019年 | 188篇 |
2018年 | 14651篇 |
2017年 | 13544篇 |
2016年 | 10225篇 |
2015年 | 849篇 |
2014年 | 613篇 |
2013年 | 1015篇 |
2012年 | 3759篇 |
2011年 | 10221篇 |
2010年 | 8899篇 |
2009年 | 6142篇 |
2008年 | 7456篇 |
2007年 | 8441篇 |
2006年 | 719篇 |
2005年 | 1770篇 |
2004年 | 1614篇 |
2003年 | 1556篇 |
2002年 | 997篇 |
2001年 | 380篇 |
2000年 | 448篇 |
1999年 | 290篇 |
1998年 | 293篇 |
1997年 | 245篇 |
1996年 | 226篇 |
1995年 | 238篇 |
1994年 | 200篇 |
1993年 | 204篇 |
1992年 | 173篇 |
1991年 | 100篇 |
1990年 | 138篇 |
1989年 | 122篇 |
1988年 | 120篇 |
1987年 | 116篇 |
1986年 | 84篇 |
1985年 | 138篇 |
1984年 | 128篇 |
1983年 | 82篇 |
1982年 | 67篇 |
1981年 | 64篇 |
1980年 | 45篇 |
1979年 | 53篇 |
1968年 | 47篇 |
1966年 | 45篇 |
1965年 | 46篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 20 毫秒
41.
Agnieszka M. Wusatowska-Sarnek Martin J. Blackburn Mark Aindow 《Materials Science and Engineering: A》2003,360(1-2):390-395
Methods are described for sample preparation of polycrystalline Ni-based superalloys in order to perform a detailed microstructural characterization. Specific techniques for the precise definition of the various phases present are outlined and these are shown to be useful for the measurement of size, volume fractions and distribution. A number of optical, scanning and transmission microscopy techniques are used to provide the necessary information. 相似文献
42.
Mark Parsons Tony Allen 《今日电子》2006,(4):44-45
对于绝大多数微控制器时钟电路而言,硅振荡器是一种简单且有效的解决方案。与晶体和陶瓷谐振器不同,基于硅材料的定时器具有抗振动、抗撞击和抗电磁干扰的优点。同时,硅振荡器不需要严格匹配的定时元件和线路板走线。 相似文献
43.
A General Role for Early Onset Cues and Intra-Event Learning; Comment on McDonald and Siegel (2004).
Research on classical conditioning with drug unconditional stimuli has had a profound effect on the understanding of general conditioning processes. The experiment reported by R. V. McDonald and S. Siegel (see record 2004-10475-001) demonstrates that cues coincident with the onset of an event can become associated with the rest of the event. This sort of learning is probably ubiquitous and has been proposed as a mechanism behind the development of panic disorder, in which interoceptive cues coincident with the start of a panic attack can be associated with the rest of the attack and can eventually come to elicit full-blown panic on their own. Evidence that extinction exposure to early onset cues can reduce their power is especially important. Drug conditioning research continues to provide a powerful testing ground for important general principles of learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
44.
45.
Dong-Soo Yoon Jae Sung Roh Sung-Man Lee Hong Koo Baik 《Journal of Electronic Materials》2003,32(8):890-898
The effect of a thin RuOx layer formed on the Ru/TiN/doped poly-Si/Si stack structure was compared with that on the RuOx/TiN/doped poly-Si/Si stack structure over the post-deposition annealing temperature ranges of 450–600°C. The Ru/TiN/poly-Si/Si
contact system exhibited linear behavior at forward bias with a small increase in the total resistance up to 600°C. The RuOx/TiN/poly-Si/Si contact system exhibited nonlinear characteristics under forward bias at 450°C, which is attributed to no
formation of a thin RuOx layer at the RuOx surface and porous-amorphous microstructure. In the former case, the addition of oxygen at the surface layer of the Ru film
by pre-annealing leads to the formation of a thin RuOx layer and chemically strong Ru-O bonds. This results from the retardation of oxygen diffusion caused by the discontinuity
of diffusion paths. In particular, the RuOx layer in a nonstoichiometric state is changed to the RuO2-crystalline phase in a stoichiometric state after post-deposition annealing; this phase can act as an oxygen-capture layer.
Therefore, it appears that the electrical properties of the Ru/TiN/poly-Si/Si contact system are better than those of the
RuOx/TiN/poly-Si/Si contact system. 相似文献
46.
47.
48.
Ting Gang Zhu Uttiya Chowdhury Michael M. Wong Jonathan C. Denyszyn Russell D. Dupuis 《Journal of Electronic Materials》2002,31(5):406-410
In this paper, we report the study of the electrical characteristics of GaN and AlGaN vertical p-i-n junctions and Schottky
rectifiers grown on both sapphire and SiC substrates by metal-organic chemical-vapor deposition. For GaN p-i-n rectifiers
grown on SiC with a relatively thin “i” region of 2 μm, a breakdown voltage over 400 V, and forward voltage as low as 4.5
V at 100 A/cm2 are exhibited for a 60-μm-diameter device. A GaN Schottky diode with a 2-μm-thick undoped layer exhibits a blocking voltage
in excess of ∼230 V at a reverse-leakage current density below 1 mA/cm2, and a forward-voltage drop of 3.5 V at a current density of 100 A/cm2. It has been found that with the same device structure and process approach, the leakage current of a device grown on a SiC
substrate is much lower than a device grown on a sapphire substrate. The use of Mg ion implantation for p-guard rings as planar-edge
terminations in mesageometry GaN Schottky rectifiers has also been studied. 相似文献
49.
The purpose of this paper is to evaluate two methods of assessing the productivity and quality impact of Computer Aided Software Engineering (CASE) and Fourth Generation Language (4GL) technologies: (1) by the retrospective method; and (2) the cross-sectional method. Both methods involve the use of questionnaire surveys. Developers' perceptions depend on the context in which they are expressed and this includes expectations about the effectiveness of a given software product. Consequently, it is generally not reliable to base inferences about the relative merits of CASE and 4GLs on a cross-sectional comparison of two separate samples of users. The retrospective method that requires each respondent to directly compare different products is shown to be more reliable. However, there may be scope to employ cross-sectional comparisons of the findings from different samples where both sets of respondents use the same reference point for their judgements, and where numerical rather than verbal rating scales are used to measure perceptions. 相似文献
50.
Jan van Eijck 《Formal Aspects of Computing》1994,6(1):766-787
Presuppositions of utterances are the pieces of information you convey with an utterance no matter whether your utterance is true or not. We first study presupposition in a very simple framework of updating propositional information, with examples of how presuppositions of complex propositional updates can be calculated. Next we move on to presuppositions and quantification, in the context of a dynamic version of predicate logic, suitably modified to allow for presupposition failure. In both the propositional and the quantificational case, presupposition failure can be viewed as error abortion of procedures. Thus, a dynamic assertion logic which describes the preconditions for error abortion is the suitable tool for analysing presupposition. 相似文献