全文获取类型
收费全文 | 3624篇 |
免费 | 58篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 30篇 |
化学工业 | 438篇 |
金属工艺 | 35篇 |
机械仪表 | 77篇 |
建筑科学 | 119篇 |
矿业工程 | 5篇 |
能源动力 | 66篇 |
轻工业 | 184篇 |
水利工程 | 19篇 |
石油天然气 | 11篇 |
无线电 | 236篇 |
一般工业技术 | 409篇 |
冶金工业 | 1726篇 |
原子能技术 | 46篇 |
自动化技术 | 285篇 |
出版年
2021年 | 23篇 |
2020年 | 19篇 |
2019年 | 22篇 |
2018年 | 31篇 |
2017年 | 25篇 |
2016年 | 28篇 |
2015年 | 37篇 |
2014年 | 33篇 |
2013年 | 106篇 |
2012年 | 64篇 |
2011年 | 83篇 |
2010年 | 73篇 |
2009年 | 68篇 |
2008年 | 95篇 |
2007年 | 97篇 |
2006年 | 70篇 |
2005年 | 70篇 |
2004年 | 67篇 |
2003年 | 61篇 |
2002年 | 60篇 |
2001年 | 58篇 |
2000年 | 62篇 |
1999年 | 92篇 |
1998年 | 459篇 |
1997年 | 302篇 |
1996年 | 208篇 |
1995年 | 114篇 |
1994年 | 95篇 |
1993年 | 106篇 |
1992年 | 47篇 |
1991年 | 49篇 |
1990年 | 35篇 |
1989年 | 50篇 |
1988年 | 51篇 |
1987年 | 33篇 |
1986年 | 40篇 |
1985年 | 55篇 |
1984年 | 42篇 |
1983年 | 35篇 |
1982年 | 41篇 |
1981年 | 57篇 |
1980年 | 31篇 |
1979年 | 30篇 |
1978年 | 31篇 |
1977年 | 78篇 |
1976年 | 152篇 |
1975年 | 30篇 |
1974年 | 18篇 |
1973年 | 31篇 |
1972年 | 20篇 |
排序方式: 共有3686条查询结果,搜索用时 187 毫秒
71.
72.
扫描笔是近年新兴的扫描产品,它又可以称为微型扫描仪或手刮式扫描笔,常见的扫描笔大小大约跟"折扇"差不多,甚者会更小。它最大的特点是携带方便,特别适合商务人士随身携带出差办公使用。一般购买它主要是用于扫描办公文件、身份证、名片或大型工程图等等。下面,小编带大家去深入了解扫描笔,让你能够知才善用。 相似文献
73.
Mark Voigtmann 《软件》2009,(1):4-4
对于一名为自动化公司提供咨询的律师来说,一件让人很不爽的事情就是有时候摆在我面前的事情是如此之多。下面是一个例子:比方说控制工程有限公司(Control Engineers Limited,CEL)希望让我就一个新项目提供一些法律意见。出现在我的收件箱中的是一份来自于CEL的客户的小礼物.其中包括一份40页的“一般条件说明”.一份5页的“特殊情况说明”.一些令人生畏的规格.以及一份打印精美的采购合同。 相似文献
74.
In the present laser processing work, the powder injection technique was investigated as a method for producing a surface metal matrix composite (MMC) containing large SiC particulates (SiCp) (105–150 m). This size is known to enhance the wear resistance of bulk aluminium-based composites. The effects of the laser-processing conditions, the powder feeding rate and the surface situations necessary to produce a well incorporated MMC on the surface were studied, and the microstructure examined. In previous work, laser processing involving the preplacement of SiCp was developed to create an AI-SiCp (45 m) MMC layer on aluminium alloy surfaces. Some of these ideas were used in conjunction with the injection process in the present work to enhance the surface-wear resistance. The wear resistance of an MMC obtained by a single laser track with the injection technique was determined and compared with the base alloy and the MMC layer produced by the preplacement technique. 相似文献
75.
This paper presents a novel method of nondestructively determining all nine elastic constants of fiber-reinforced orthotropic plate specimens. Group velocities of bulk quasi-longitudinal (QL), pure transverse (PT), and surface skimming pseudo-longitudinal modes are measured in glass-fiber (GF) and carbon-fiber (CF) reinforced Poly Ether Ether Ketone (PEEK) specimens by a point-source/point-receiver (PS/PR) technique. First, the pure index longitudinal moduliC
11,C
22, andC
33, are obtained from the longitudinal (L) group velocities measured in three principal directions. Next, the pure index shear moduli,C
44,C
55, andC
66, are determined by measuring the shear horizontally (SH) polarized PT group velocities in the symmetry planes. Finally, the mixed index elastic constantsC
ij
(i j) are calculated from QL group velocities measured in the symmetry planes and using analytic formulas. 相似文献
76.
J. W. Gassett D. P. Wiesler A. G. Baker D. A. Osborn K. V. Miller R. L. Marchinton M. Novotny 《Journal of chemical ecology》1996,22(9):1689-1696
Interdigital secretions were collected from eight male white-tailed deer of various ages. Analysis of volatiles was performed by gas chromatography-mass spectrometry with a modified headspace technique. Forty-six volatile compounds were found including alkanes, arenes, aldehydes, ketones, aliphatic acids, esters, pyrroles, furans, and sulfur compounds. Eleven occurred in higher concentrations (P0.10) in dominant (3.5-year-old) than in subordinate (1.5-year-old) animals. Dominant males typically have higher serum testosterone levels, and fatty acids and esters fluctuate with sebum production, which is under hormonal control. Therefore, these compounds may reflect testosterone levels and act as chemical signals indicating the presence of a dominant male. Interdigital volatiles also may act as generalized scent trail markers. 相似文献
77.
We describe the development and testing of a holographic projection system that is used to produce micro-optical devices. The projector uses a two-dimensional two-phase-level diffraction grating to produce multiple coherent beams and an interferometric optical system behind the grating to recombine the beams to produce interference patterns that have been recorded within a photosensitive substrate. The two different substrates that we used are a diazo imaging material and a bisbenzocyclobutene (BCB) polymeric resin for fabrication of surface relief microstructures. After the exposed photosensitive substrate is developed, the recorded interference pattern forms a micro-optical device. The analysis and testing of these micro-optical devices show promise that this technique can form patterns uniformly over a region of several centimeters in diameter on flat or curved substrates. The experimental testing results of these micro-optical devices demonstrate that this method is a simple and energy efficient system to produce microstructures compared with other methods. These devices may be used as a new generation of directional light filters or monolithic microlenslet arrays that may have applications in communications, display, and components technologies. 相似文献
78.
Sleep in a live-in mining operation: The influence of start times and restricted non-work activities
The amount of sleep obtained between shifts is influenced by numerous factors including the length of work and rest periods, the timing of the rest period relative to the endogenous circadian cycle and personal choices about the use of non-work time. The current study utilised a real-world live-in mining environment to examine the amount of sleep obtained when access to normal domestic, family and social activities was restricted. Participants were 29 mining operators (26 male, average age 37.4 ± 6.8 years) who recorded sleep, work and fatigue information and wore an activity monitor for a cycle of seven day shifts and seven night shifts (both 12 h) followed by either seven or fourteen days off. During the two weeks of work participants lived on-site. Total sleep time was significantly less (p < 0.01) while on-site on both day (6.1 ± 1.0 h) and night shifts (5.7 ± 1.5 h) than days off (7.4 ± 1.4 h). Further, night shift sleep was significantly shorter than day-shift sleep (p < 0.01). Assessment of subjective fatigue ratings showed that the sleep associated with both days off and night shifts had a greater recovery value than sleep associated with day shifts (p < 0.01). While on-site, participants obtained only 6 h of sleep indicating that the absence of competing domestic, family and social activities did not convert to more sleep. Factors including shift start times and circadian influences appear to have been more important. 相似文献
79.
Jerry L. Trahan Mingxian Jin Wittaya Chantamas Johnnie W. Baker 《Journal of Parallel and Distributed Computing》2010
The MASC (Multiple ASsociative Computing) model is a multi-SIMD model that uses control parallelism to coordinate the interaction of data parallel threads and supports associative SIMD computing on each of its threads. There have been a wide range of algorithms developed for this model. Research on using this model in real-time system applications and building a scalable MASC architecture is currently quite active. In this paper, we present simulations between MASC and reconfigurable bus-based models, e.g., various versions of the Reconfigurable Multiple Bus Machine (RMBM). Constant time simulations of the basic RMBM by MASC and vice versa are obtained. Simulations of the segmenting RMBM, fusing RMBM, and extended RMBM by MASC in non-constant time are also discussed. By taking advantage of previously established relationships between RMBM and two other popular parallel computational models, namely, the Reconfigurable Mesh (RM) and the Parallel Random Access Machine (PRAM), we extend our simulation results to further categorize the power of the MASC model in relation to RM and PRAM. 相似文献
80.
This paper describes the inter-rater and intra-rater reliability, and the concurrent validity of an observational instrument, the Keyboard Personal Computer Style instrument (K-PeCS), which assesses stereotypical postures and movements associated with computer keyboard use. Three trained raters independently rated the video clips of 45 computer keyboard users to ascertain inter-rater reliability, and then re-rated a sub-sample of 15 video clips to ascertain intra-rater reliability. Concurrent validity was assessed by comparing the ratings obtained using the K-PeCS to scores developed from a 3D motion analysis system. The overall K-PeCS had excellent reliability [inter-rater: intra-class correlation coefficients (ICC)=.90; intra-rater: ICC=.92]. Most individual items on the K-PeCS had from good to excellent reliability, although six items fell below ICC=.75. Those K-PeCS items that were assessed for concurrent validity compared favorably to the motion analysis data for all but two items. These results suggest that most items on the K-PeCS can be used to reliably document computer keyboarding style. 相似文献