全文获取类型
收费全文 | 2243篇 |
免费 | 9篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 27篇 |
综合类 | 1篇 |
化学工业 | 131篇 |
金属工艺 | 19篇 |
机械仪表 | 20篇 |
建筑科学 | 25篇 |
矿业工程 | 1篇 |
能源动力 | 14篇 |
轻工业 | 65篇 |
水利工程 | 6篇 |
石油天然气 | 2篇 |
无线电 | 129篇 |
一般工业技术 | 139篇 |
冶金工业 | 1526篇 |
原子能技术 | 4篇 |
自动化技术 | 146篇 |
出版年
2021年 | 11篇 |
2018年 | 6篇 |
2017年 | 5篇 |
2016年 | 8篇 |
2015年 | 5篇 |
2014年 | 14篇 |
2013年 | 41篇 |
2012年 | 23篇 |
2011年 | 40篇 |
2010年 | 30篇 |
2009年 | 25篇 |
2008年 | 39篇 |
2007年 | 28篇 |
2006年 | 35篇 |
2005年 | 32篇 |
2004年 | 33篇 |
2003年 | 25篇 |
2002年 | 26篇 |
2001年 | 26篇 |
2000年 | 24篇 |
1999年 | 75篇 |
1998年 | 475篇 |
1997年 | 268篇 |
1996年 | 157篇 |
1995年 | 100篇 |
1994年 | 93篇 |
1993年 | 89篇 |
1992年 | 27篇 |
1991年 | 31篇 |
1990年 | 37篇 |
1989年 | 26篇 |
1988年 | 33篇 |
1987年 | 30篇 |
1986年 | 25篇 |
1985年 | 28篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 17篇 |
1981年 | 22篇 |
1980年 | 21篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1977年 | 44篇 |
1976年 | 93篇 |
1975年 | 6篇 |
1974年 | 7篇 |
1973年 | 7篇 |
1972年 | 6篇 |
1971年 | 3篇 |
1970年 | 6篇 |
排序方式: 共有2255条查询结果,搜索用时 15 毫秒
51.
Systematic and quantitative management of work-related fatigue within workplaces has been a challenging task due to a lack of useful tools. A previous paper provided background and development of a work-related fatigue modelling approach. The current paper outlines model evaluations using sleep deprivation experiments and recommendations of work scheduling. Previous studies have reported cumulative effects of sleep restriction (4-5 h per night) on a number of measures. Model predictions were correlated against psychomotor vigilance task lapses (r = 0.92) and reaction time responses (slowest 10%, r = 0.91) as well as sleep latency (r = -0.97). Further correlations were performed on four measures from a 64 h continuous sleep deprivation study; that is objective vigilance (r = -0.75) as well as subjective performance (r = -0.75), sleepiness (r = 0.82) and tiredness (r = 0.79). Evaluation against current scheduling recommendations illustrated consistency with the literature with the exception that forward rotation did not provide benefits over backward rotation. The results indicate that model predictions correlate well across a range of objective and subjective measures. This relationship also appears to hold for cumulative and continuous sleep deprivation protocols. Future studies will also focus on field-based evaluation. 相似文献
52.
This paper reviews our current knowledge and understanding of carbon processes in the terrestrial ecosystem with a view to reducing soil carbon losses by optimising land-use and land management. Processes that influence the fate of carbon (in both terms of quantity and quality) are important in determining soil fertility, quality and health as well as consequences for future environmental change scenarios. We need to understand the processes that determine soil carbon losses and the fate of the carbon once lost from the soil in order to provide sustainable solutions for mitigating these carbon losses as part of land management "best practice" and balancing national carbon budgets. Here we review the amount of carbon within the UK terrestrial pool, the processes involved and factors influencing carbon transport to and from soils, the fate of the carbon once it has been lost from the soil environment and land-use scenarios that affect carbon losses. We conclude with possible management options to reduce soil carbon loss and identify gaps in knowledge in order to better understand carbon processes in the terrestrial environment. 相似文献
53.
H J Howard E P Aalseth G D Adams L J Bush R W McNew L J Dawson 《Journal of dairy science》1987,70(8):1563-1571
From 10 +/- 3.5 d after parturition to 149 +/- 3.5 d of lactation, 146 cows (109 Holstein and 37 Ayrshires) were fed either a 15 or 20% crude protein diet of 45% sorghum silage and 55% concentrate. Milk production was enhanced by the 20% protein diet, but percentage of milk fat and protein were unchanged. Average daily intake of DM was unaffected by diet. Actual decreases in body weight and condition were small, although cows on 15% protein lost more condition. Concentration of plasma urea nitrogen increased rapidly during the first 4 wk of the experiment with cows on the 20% protein diet maintaining a 10 mg/dl advantage after the 4th wk on experiment. Diet did not affect the postpartum interval to first normal corpus luteum and standing estrus. Cows were inseminated artificially between 55 and 145 d post-calving with one freeze batch of semen from one bull of each appropriate breed mainly by one inseminator. Overall, days open, services per conception, and percentage cows pregnant on experiment were 80, 1.40, and 85, respectively. Concentration of protein in the diet did not affect these reproductive traits. There was no conflict between the amount of dietary protein provided for lactation and reproduction in this experiment. 相似文献
54.
55.
RD Rosenberg WC Hunt MR Williamson FD Gilliland PW Wiest CA Kelsey CR Key MN Linver 《Canadian Metallurgical Quarterly》1998,209(2):511-518
PURPOSE: To examine how common patient factors affect screening mammographic sensitivity and cancer stage at diagnosis. MATERIALS AND METHODS: The authors used a population-based database of 183,134 screening mammograms and a statewide tumor registry to identify 807 breast cancers detected at screening mammography. RESULTS: Sensitivity varied significantly with ethnicity, use of estrogen replacement therapy, mammographic breast density, and age. Sensitivity was 54% (13 of 24) in women younger than 40 years, 77% (121 of 157) in women aged 40-49 years, 78% (224 of 286) in women aged 50-64 years, and 81% (277 of 340) in women older than 64 years. Sensitivity was 68% (162 of 237) for dense breasts and 85% (302 of 356) for nondense breasts and 74% (180 of 244) in estrogen replacement therapy users and 81% (417 of 513) in nonusers. Sensitivity was most markedly reduced with the combination of dense breasts and estrogen replacement therapy use; there was little difference when only one factor was present. Median cancer size and the percentage of early cancers showed little change with any factors. CONCLUSION: Age is a minor determinant of mammographic sensitivity in women aged 40 years or older. Sensitivity is substantially decreased with the combination of higher breast density and estrogen replacement therapy use. There was not a notable shift in cancer outcomes in the groups with lower mammographic sensitivity. These data do not support different screening recommendations in women aged 40-49 years or in estrogen replacement therapy users. 相似文献
56.
57.
58.
Dawson K Strutwolf J Rodgers KP Herzog G Arrigan DW Quinn AJ O'Riordan A 《Analytical chemistry》2011,83(14):5535-5540
In this work, we fabricate gold nanowires with well controlled critical dimensions using a recently demonstrated facile approach termed nanoskiving. Nanowires are fabricated with lengths of several hundreds of micrometers and are easily electrically contacted using overlay electrodes. Following fabrication, nanowire device performance is assessed using both electrical and electrochemical characterization techniques. We observe low electrical resistances with typical linear Ohmic responses from fully packaged nanowire devices. Steady-state cyclic voltammograms in ferrocenemonocarboxylic acid demonstrate scan rate independence up to 1000 mV s(-1). Electrochemical responses are excellently described by classical Butler-Volmer kinetics, displaying a fast, heterogeneous electron transfer kinetics, k(0) = 2.27 ± 0.02 cm s(-1), α = 0.4 ± 0.01. Direct reduction of hydrogen peroxide is observed at nanowires across the 110 pM to 1 mM concentration range, without the need for chemical modification, demonstrating the potential of these devices for electrochemical applications. 相似文献
59.
Azar R. Udrea F. De Silva M. Amaratunga G. Wai Tung Ng Dawson F. Findlay W. Waind P. 《Industry Applications, IEEE Transactions on》2004,40(3):710-716
An enhanced insulated gate bipolar transistor (IGBT) model based on the Kraus model with new derivations based on an extra parameter accounting for p-i-n injection was developed to allow simulation of both trench and DMOS IGBT structures. Temperature dependence was also implemented in the model. The model was validated against steady-state and transient measurements done on an 800-A 1.7-kV Dynex IGBT module at 25/spl deg/C and 125/spl deg/C. The Spice model has also shown excellent agreement with mixed mode MEDICI simulations. The Spice model also takes into account for the first time the parasitic thyristor effect allowing the dc and dynamic temperature-dependent latchup modeling of power modules as well as their temperature-dependent safe operating area. 相似文献
60.
Thanchanok Ratvijitvech Robert Dawson Andrea Laybourn Yaroslav Z. Khimyak Dave J. Adams Andrew I. Cooper 《Polymer》2014
Control over the surface functionality and microporosity in conjugated microporous polymers (CMPs) has been achieved by the post-synthetic modification of amines into amides of with different alkyl chains, one of which was chiral. The surface areas, pore volumes, carbon dioxide uptakes and isosteric heat of adsorption for carbon dioxide can be rationally tuned. 相似文献