全文获取类型
收费全文 | 3579篇 |
免费 | 79篇 |
专业分类
电工技术 | 57篇 |
综合类 | 4篇 |
化学工业 | 765篇 |
金属工艺 | 83篇 |
机械仪表 | 60篇 |
建筑科学 | 136篇 |
矿业工程 | 24篇 |
能源动力 | 107篇 |
轻工业 | 205篇 |
水利工程 | 34篇 |
石油天然气 | 15篇 |
无线电 | 291篇 |
一般工业技术 | 533篇 |
冶金工业 | 907篇 |
原子能技术 | 39篇 |
自动化技术 | 398篇 |
出版年
2021年 | 43篇 |
2020年 | 24篇 |
2019年 | 29篇 |
2018年 | 45篇 |
2017年 | 37篇 |
2016年 | 61篇 |
2015年 | 35篇 |
2014年 | 56篇 |
2013年 | 230篇 |
2012年 | 88篇 |
2011年 | 138篇 |
2010年 | 107篇 |
2009年 | 121篇 |
2008年 | 136篇 |
2007年 | 128篇 |
2006年 | 113篇 |
2005年 | 114篇 |
2004年 | 88篇 |
2003年 | 88篇 |
2002年 | 76篇 |
2001年 | 72篇 |
2000年 | 39篇 |
1999年 | 75篇 |
1998年 | 191篇 |
1997年 | 112篇 |
1996年 | 96篇 |
1995年 | 82篇 |
1994年 | 70篇 |
1993年 | 63篇 |
1992年 | 56篇 |
1991年 | 41篇 |
1990年 | 45篇 |
1989年 | 39篇 |
1988年 | 28篇 |
1987年 | 39篇 |
1986年 | 37篇 |
1985年 | 50篇 |
1984年 | 39篇 |
1983年 | 40篇 |
1982年 | 37篇 |
1981年 | 41篇 |
1980年 | 49篇 |
1979年 | 40篇 |
1978年 | 32篇 |
1977年 | 45篇 |
1976年 | 60篇 |
1975年 | 48篇 |
1974年 | 51篇 |
1973年 | 21篇 |
1972年 | 23篇 |
排序方式: 共有3658条查询结果,搜索用时 15 毫秒
21.
The design and evaluation of an optically triggered, fully integrated sample and hold circuit (OS/H) is described. Measured results are presented that demonstrate operation of this circuit at 250 Ms/s and with effective resolution approaching 8 bits. The integrated circuit, which measures 2.1 mm×1.4 mm, is realized in -1.0-V threshold, 20-GHz ft GaAs MESFET technology, consumes approximately 200 mW of power, and requires one optical address. The OS/H will find applications in high precision, hybrid, and integrated signal processing systems where high speed, high levels of parallelism, and low timing jitter are important. Measured results of a series photoconducting (Auston switch) OS/H realized in the same technology are presented for comparison purposes 相似文献
22.
Ralph W. Pridmore 《Color research and application》2007,32(3):208-222
A color stimulus may be characterized by three psychophysical dimensions (luminance, dominant wavelength, and purity), whose corresponding color attributes are lightness, hue, and chroma/colorfulness. The 3 × 3 matrix gives nine basic effects of the psychophysical dimensions on the color attributes (e.g. the effect of luminance on hue), but there are 49 possible combinations as more complex effects (e.g. the effect of luminance on hue and chroma, i.e. on chromaticity). Researching and quantifying such effects enables modelling of the underlying neural mechanisms and of color appearance. Using a simple nomenclature to identify the effects (e.g. Ph denotes the effect of Purity on hue), this paper briefly reviews and interrelates 15 of the commonest effects, giving new data or new graphical perspectives to clarify or fill gaps in the literature. Contrast and no‐contrast effects (stimuli viewed simultaneously or singly, respectively) are differentiated. © 2007 Wiley Periodicals, Inc. Col Res Appl, 32, 208–222, 2007 相似文献
23.
Basicity values have been determined for series of monoazo dyes incorporating a pyrrolidino or a piperidino moiety. In general, the pKa value is found to decrease as the donor capacity of the terminal nitrogen atom decreases.The basicities of the 4'-substituted piperidinoazobenzenes decrease as the electron withdrawing strength of the 4'-substituent increases. However, the pKa values of the related pyrrolidino compounds appear to be insensitive to the substituent. 相似文献
24.
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
25.
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
26.
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
27.
In enteric bacteria, chromosomally encoded permeases specific for lactose, maltose, and melibiose are allosterically regulated by the glucose-specific enzyme IIA of the phosphotransferase system. We here demonstrate that the plasmid-encoded raffinose permease of enteric bacteria is similarly subject to this type of inhibition. 相似文献
28.
A study of eight deaths involving the benzodiazepine flunitrazepam was performed to assess the contribution of this drug to the fatalities. Coronial deaths in Victoria in the 2-year period to mid-1991 were selected in which either flunitrazepam or flunitrazepam and ethanol were the principal toxicological findings. All bodies were subject to a full autopsy by forensic pathologists, and a full toxicological examination. No significant pathology was found at autopsy in any case. Very high concentrations of 7-aminoflunitrazepam, a metabolite of flunitrazepam, were present in all cases. In four cases no other significant drug was detected, whereas in the other four cases there were significant concentrations of ethanol (mean 1.6 g/L). In these two groups of cases the concentrations of 7-aminoflunitrazepam were 0.45 mg/L and 0.16 mg/L, respectively. Only moderate levels of flunitrazepam were detected, suggesting that 7-aminoflunitrazepam is produced postmortem and may be an important marker of flunitrazepam usage. The causes of death in these eight cases were probably either flunitrazepam toxicity or a combination of flunitrazepam and ethanol toxicity. Only one case appeared likely to have been a suicide. Our observations in these cases suggest that flunitrazepam may cause death in the absence of other drugs or significant disease. The presence of ethanol reduces the amount of flunitrazepam needed to cause death. 相似文献
29.
30.
Tim Baines Stephen Mason Peer-Olaf Siebers John Ladbrook 《Simulation Modelling Practice and Theory》2004,12(7-8):515
Computer based discrete event simulation (DES) is one of the most commonly used aids for the design of automotive manufacturing systems. However, DES tools represent machines in extensive detail, while only representing workers as simple resources. This presents a problem when modelling systems with a highly manual work content, such as an assembly line. This paper describes research at Cranfield University, in collaboration with the Ford Motor Company, founded on the assumption that human variation is the cause of a large percentage of the disparity between simulation predictions and real world performance. The research aims to improve the accuracy and reliability of simulation prediction by including models of human factors. 相似文献