全文获取类型
收费全文 | 20716篇 |
免费 | 1353篇 |
国内免费 | 11篇 |
专业分类
电工技术 | 379篇 |
综合类 | 55篇 |
化学工业 | 4716篇 |
金属工艺 | 641篇 |
机械仪表 | 520篇 |
建筑科学 | 974篇 |
矿业工程 | 145篇 |
能源动力 | 407篇 |
轻工业 | 2895篇 |
水利工程 | 165篇 |
石油天然气 | 35篇 |
无线电 | 1300篇 |
一般工业技术 | 5428篇 |
冶金工业 | 939篇 |
原子能技术 | 194篇 |
自动化技术 | 3287篇 |
出版年
2023年 | 258篇 |
2022年 | 174篇 |
2021年 | 441篇 |
2020年 | 367篇 |
2019年 | 352篇 |
2018年 | 700篇 |
2017年 | 700篇 |
2016年 | 791篇 |
2015年 | 647篇 |
2014年 | 805篇 |
2013年 | 1689篇 |
2012年 | 980篇 |
2011年 | 1207篇 |
2010年 | 1024篇 |
2009年 | 937篇 |
2008年 | 1058篇 |
2007年 | 1028篇 |
2006年 | 752篇 |
2005年 | 604篇 |
2004年 | 492篇 |
2003年 | 490篇 |
2002年 | 488篇 |
2001年 | 414篇 |
2000年 | 341篇 |
1999年 | 280篇 |
1998年 | 256篇 |
1997年 | 264篇 |
1996年 | 221篇 |
1995年 | 221篇 |
1994年 | 177篇 |
1993年 | 152篇 |
1992年 | 159篇 |
1991年 | 126篇 |
1990年 | 108篇 |
1989年 | 111篇 |
1988年 | 106篇 |
1987年 | 104篇 |
1986年 | 86篇 |
1985年 | 188篇 |
1984年 | 193篇 |
1983年 | 142篇 |
1982年 | 138篇 |
1981年 | 167篇 |
1980年 | 129篇 |
1979年 | 119篇 |
1978年 | 114篇 |
1977年 | 102篇 |
1976年 | 105篇 |
1975年 | 118篇 |
1974年 | 104篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
111.
Vergleich der Extrakte und des Lignins aus frischem und gelagertem Kiefernholz (Pinus sylvestris L.)
The degradation processes of the extractives of pine wood caused by aging are only noticeable in the heartwood. In seasoned sapwood the percentages of the water extracts and the cyclohexane-ethanol extract increase compared with the green sample; the alkali extracts, however, do not vary. The contents of acid lignin as well as the UV and IR spectra of MWL do not show differences. The amount of OCH3/C9 is in all samples 0.96, but the degree of oxidation is higher in the seasoned wood than in the green one. 相似文献
112.
Ernst Pöppel 《Informatik-Spektrum》2002,73(6):427-437
113.
The man-machine dialog is very important for the design process. In this paper a program system, based on the minicomputer KRS 4201 (ROBOTRON), is demonstrated by using an interactive graphical screen. This program system provides the opportunity to analyze and synthesize mechanisms up to 16 links. The application is demonstrated by designing a front-loader-system for a truck. Real-time animation of seven-bar linkages and coupler curves, including velocity and acceleration, are shown. 相似文献
114.
Structured document storage and refined declarative and navigational access mechanisms in HyperStorM 总被引:2,自引:0,他引:2
Klemens Böhm Karl Aberer Erich J. Neuhold Xiaoya Yang 《The VLDB Journal The International Journal on Very Large Data Bases》1997,6(4):296-311
The combination of SGML and database technology allows to refine both declarative and navigational access mechanisms for
structured document collection: with regard to declarative access, the user can formulate complex information needs without
knowing a query language, the respective document type definition (DTD) or the underlying modelling. Navigational access is
eased by hyperlink-rendition mechanisms going beyond plain link-integrity checking. With our approach, the database-internal
representation of documents is configurable. It allows for an efficient implementation of operations, because DTD knowledge
is not needed for document structure recognition. We show how the number of method invocations and the cost of parsing can
be significantly reduced.
Edited by Y.C. Tay. Received April 22, 1996 / Accepted March 16, 1997 相似文献
115.
James L. Smialek Ph.D. Frances A. Archer B.S. Ralph G. Garlick B.S. 《JOM Journal of the Minerals, Metals and Materials Society》1994,46(12):39-41
Helicopter turbine engines used in the Desert Shield and Desert Storm operations experienced excessive sand ingestion. Fine particles were able to bypass filters and proceed through the combustor or cooling gaspaths. The first-stage turbine vanes were impacted with viscous silicate particles, forming a deposit on the leading-edge root platform and resulting in overheating and oxidation. The chemistry of the raw sand determines that of the ingested powders, the deposits, and the material reactions. 相似文献
116.
The lattice constants of boron carbides have been determined by powder X-ray diffraction for samples with compositions between about 7.7 and 20.5 at.% carbon. The boundaries of the single-phase region are at about 9 at.% carbon and near, but likely somewhat less than, 20 at.% carbon. The composition dependence of the lattice constants thus established provides a method of assessing the carbon concentration of unknown materials. In particular, assignment of the approximate composition of single crystals used in previous studies allows for a systematic examination of changes in interatomic separation as a function of composition. These changes are discussed in terms of a structural model of the boron carbide solid solution. 相似文献
117.
Daniel Röhnert Fritz Phillipp Helfried Reuther Till Weber Egbert Wessel Michael Schütze 《Oxidation of Metals》2007,68(5-6):271-293
The initial stages of the metal-dusting process on Alloy 800 at 620 °C were investigated by light optical microscopy, RAMAN
spectroscopy, atomic-force microscopy, Auger electron spectroscopy, transmission-electron microscopy and electron back-scatter
diffraction. As it turned out the incubation period for metal-dusting is characterized by simultaneous formation of a heterogeneously
growing oxide scale and deposition of carbon. The material surface shows different tarnish colors depending on the substrate-grain
orientation with different susceptibility to the beginning of metal-dusting attack. “Low-index” grains were not attacked within
the times investigated while the other grain orientations showed pitting. Carbon is evidently incorporated into the oxide
scale from the very beginning of exposure with different intensities depending on the underlying substrate-grain orientation
leading to differences in the tarnish colors. As a consequence carbides are formed even underneath “dense” oxide layers. Evidently
metal-dusting attack starts at positions of the oxide scale where “higher carbon concentrations” are present. 相似文献
118.
119.
K. Fröhlich 《e & i Elektrotechnik und Informationstechnik》2002,119(1):15-21
It is discussed to what extent tools, provided by modern information technology, reasonably improve the performance of high voltage circuit breakers in transmission systems of electric power. Controlled switching, properly applied, has a high potential to increase life expectancy of the breaker itself and of the adjacent equipment. Power quality can also be improved. The technical advantage of controlled switching is beyond doubt, although the economic benefits are not easily quantified. In terms of breaker intelligence, another very important aspect is condition diagnosis. In particular a model based diagnosis seems to point to the future. Condition diagnosis giving maintainance requirements and pre-warning of impending failures should facilitate the tasks of the operating personnel. As a conclusion it can be stated that more intelligence of circuit breakers would be useful. 相似文献
120.
Ga -Er Yu J. Parrick M. Edirisinghe D. Finch B. Ralph 《Journal of Materials Science》1994,29(6):1680-1685
Proton nuclear magnetic resonance (1H NMR) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and gas chromatography (GC) have been used to study the products of ammonolysis of dichloromethylsilane in diethyl ether at 0 °C. Results indicate that the major products are trimethylcyclotrisilazane and tetramethylcyclotetrasilazane. Hydrolysis of the cyclosilazanes has also been qualitatively investigated. A simple and useful method for the identification of cyclosilazanes has been developed using the 1H NMR technique. 相似文献