全文获取类型
收费全文 | 9074篇 |
免费 | 434篇 |
国内免费 | 19篇 |
专业分类
电工技术 | 111篇 |
综合类 | 19篇 |
化学工业 | 1786篇 |
金属工艺 | 234篇 |
机械仪表 | 363篇 |
建筑科学 | 248篇 |
矿业工程 | 29篇 |
能源动力 | 393篇 |
轻工业 | 926篇 |
水利工程 | 50篇 |
石油天然气 | 14篇 |
武器工业 | 1篇 |
无线电 | 1309篇 |
一般工业技术 | 1680篇 |
冶金工业 | 959篇 |
原子能技术 | 66篇 |
自动化技术 | 1339篇 |
出版年
2024年 | 15篇 |
2023年 | 100篇 |
2022年 | 142篇 |
2021年 | 253篇 |
2020年 | 216篇 |
2019年 | 197篇 |
2018年 | 250篇 |
2017年 | 258篇 |
2016年 | 289篇 |
2015年 | 256篇 |
2014年 | 379篇 |
2013年 | 609篇 |
2012年 | 558篇 |
2011年 | 624篇 |
2010年 | 498篇 |
2009年 | 488篇 |
2008年 | 530篇 |
2007年 | 438篇 |
2006年 | 340篇 |
2005年 | 304篇 |
2004年 | 271篇 |
2003年 | 259篇 |
2002年 | 219篇 |
2001年 | 152篇 |
2000年 | 159篇 |
1999年 | 158篇 |
1998年 | 366篇 |
1997年 | 228篇 |
1996年 | 184篇 |
1995年 | 120篇 |
1994年 | 92篇 |
1993年 | 98篇 |
1992年 | 54篇 |
1991年 | 43篇 |
1990年 | 35篇 |
1989年 | 41篇 |
1988年 | 37篇 |
1987年 | 37篇 |
1986年 | 19篇 |
1985年 | 31篇 |
1984年 | 20篇 |
1983年 | 22篇 |
1982年 | 10篇 |
1981年 | 17篇 |
1980年 | 16篇 |
1979年 | 8篇 |
1978年 | 14篇 |
1977年 | 16篇 |
1976年 | 17篇 |
1972年 | 7篇 |
排序方式: 共有9527条查询结果,搜索用时 8 毫秒
41.
J Jiménez-Castellanos A Carmona L Castellanos CJ Catalina-Herrera 《Canadian Metallurgical Quarterly》1995,17(2):139-43, 14-6
In the present paper we have studied the gross (mesoscopic) anatomy of the ophthalmic a. in humans, using magnification by microsurgical systems to obtain data on the origin and course of this artery and its main collateral branches. Comparison of our results with previous reports indicates that, although the anatomical variations of the vascular system are well known, some patterns of frequency may be emphasised. Thus, the ophthalmic a. was usually found as a collateral branch of the internal carotid a., although other origins were also found. The ophthalmic a., once inside the orbit, followed a course above the optic nerve in most cases. All the collateral branches of the ophthalmic a., with the exception of the muscular branches, showed great constancy. 相似文献
42.
A micellar electrokinetic capillary chromatographic (MECC) method has been developed and optimised for the separation of 5-aminolaevulinic acid (ALA) and porphobilinogen (PBG). The running buffer consisted of a mixture of 20 mM sodium phosphate and 20 mM sodium borate containing 50 mM sodium dodecyl sulphate (SDS) adjusted to pH 9.5 with 1 M NaOH. The running voltage and temperature were 20-25 kV and 30 degrees C, respectively. The MECC method for the analysis of PBG is fast and simple and is useful for the screening of PBG in the urine of patients suspected to have acute intermittent porphyria (AIP), and for the confirmation of lead exposure by measuring red-cell ALA-dehydratase (ALA-D) activity with ALA as the enzyme substrate. 相似文献
43.
"Mega"-analysis was developed by M. Carlson and N. Miller (see record 1987-31249-001) as an extension of traditional meta-analytic procedures for conducting integrative reviews of existing research literatures. One such mega-analysis was conducted by Carlson and Miller to synthesize the literature on the relation between negative mood states and helping. That analysis found no support for a theoretical account (negative state relief) that had been confirmed previously by using various experimental approaches. In an attempt to reconcile the discrepancy, the logic and methods used in Carlson and Miller's mega-analysis of the negative mood-helping literature were examined, and several serious problems were found. These problems are discussed, and data are presented to show that the results of that mega-analysis, and perhaps all mega-analyses, should not be viewed with confidence. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
44.
45.
M. Jiménez-Melendo J. P. Riviére T. Suzuki H. Koizumi J. Castaing A. Domínguez-Rodríguez 《Journal of Materials Science》1992,27(13):3589-3593
NiO single crystals prepared by two crystal growth techniques (zone melting in an arc-image furnace and Verneuil crystallization have been deformed by compression along 001 at temperatures as low as 4.2 K, and the dislocation substructure observed by transmission electron microscopy. The Peierls mechanism has been suggested as the mechanism controlling the mechanical behaviour at the lower temperatures. The dislocations generated at cavities found in the zone-melted crystals may be responsible for the increase of the flow stress of these crystals compared with the Verneuil ones. 相似文献
46.
Current applications of electronic performance monitoring based on job design theories that consider worker performance rather than stress issues are likely to generate unsatisfying and stressful jobs (Smith et al, 1986). This study examines critical job design elements that could influence worker stress responses in an electronic monitoring context. A questionnaire survey of employees in telecommunications companies representative of each region in the United States examined job stress in directory assistance, service representative and clerical jobs with specific emphasis on the influence of electronic monitoring of job performance, satisfaction and employee health. Useable surveys were received from 745 employees representing seven operating companies and AT & T; a response rate of about 25%. The results of this survey indicated that employees who had their performance electronically monitored perceived their working conditions as more stressful, and reported higher levels of job boredom, psychological tension, anxiety, depression, anger, health complaints and fatigue. It is postulated that these effects may be related to changes in job design due to electronic performance monitoring. 相似文献
47.
The overall non-isothermal crystallization kinetics for nucleated and non-nucleated isotactic polypropylene (iPP) in dotriacontane systems was investigated. Adipic acid was used as the nucleating agent. Crystallization peak temperature was determined via differential scanning calorimetry as a function of the experimentally controlled variables iPP concentration, cooling rate, and nucleating agent concentration. The influence of these variables on crystallization mechanism and spherulitic structure as implied by the Ozawa and Ziabicki analyses was determined. The non-isothermal crystallization kinetics presented here are the first for iPP-diluent systems with and without nucleating agent. 相似文献
48.
The simple criterion proposed by Chandnani and Epstein (1984, 1986) for stable spouting, dor/dp ≤ 25.4, is shown to give a good separation between gas-solid systems which form permanent jets and those that bubble, for a wide range of experimental data reported in the literature. The criterion is suggested as a necessary but not sufficient condition for permanent jet formation in fluidized, spout-fluid and spouted beds. 相似文献
49.
This paper proposes a tactile display providing both shear and normal feedback to the fingertip for generating three-axis tactile feedback during teleoperation of a surgical robot. The display is composed of five balloons actuated by controlling the pneumatic pressure. The implemented display is 18?mm?×?18?mm?×?15?mm. This size is suitable for mounting the display onto the master controls of a surgical robot. The maximum normal and shear displacements are 2 and 1.3?mm, respectively. The proposed tactile display may provide perceivable stimuli to a human finger pad in all five directions: normal, distal, proximal, radial, and ulnar. This paper also reports on the results of psychophysical measurement of the minimum perceivable movement of the developed tactile display for each of the five directions. 相似文献
50.
The purpose of this study was to perform a systematic and comprehensive comparison between the recommended weights of lift (RWL) from the revised NIOSH lifting equation, and the specific biomechanical, psychophysical and physiological criteria that were stated to be used in the equation's development. A composite acceptable load (CAL) table was developed for the 216 conditions presented in the female lifting table of Snook and Ciriello (1991). Each CAL value was calculated to correspond to the most conservative load of the three design criteria. The RWLs caused lumbar compression forces close to the biomechanical limit of 3400 N for lifts below knuckle height, but resulted in compression forces that are much lower at higher lifting heights. At moderate lifting frequencies, the average RWL would be acceptable to more than 95% of female workers according to the psychophysical criterion. At the highest frequencies, the RWL was found to be an average of 63% of the CAL values based on the integration of the psychophysical and physiological criteria. It is recommended that ergonomists acknowledge the very conservative nature of the revised NIOSH lifting equation when using it to evaluate occupational lifting tasks. 相似文献