首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2243篇
  免费   9篇
  国内免费   3篇
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
  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.
Fletcher A  Dawson D 《Ergonomics》2001,44(5):475-488
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.
Carbon losses from soil and its consequences for land-use management   总被引:5,自引:0,他引:5  
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.
Influence of dietary protein on reproductive performance of dairy cows   总被引:1,自引:0,他引:1  
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.
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.
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.
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.
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   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号