全文获取类型
收费全文 | 816篇 |
免费 | 20篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 10篇 |
综合类 | 5篇 |
化学工业 | 95篇 |
金属工艺 | 11篇 |
机械仪表 | 17篇 |
建筑科学 | 30篇 |
矿业工程 | 8篇 |
能源动力 | 17篇 |
轻工业 | 59篇 |
水利工程 | 4篇 |
石油天然气 | 2篇 |
无线电 | 85篇 |
一般工业技术 | 113篇 |
冶金工业 | 227篇 |
原子能技术 | 8篇 |
自动化技术 | 152篇 |
出版年
2023年 | 4篇 |
2022年 | 12篇 |
2021年 | 9篇 |
2020年 | 14篇 |
2019年 | 6篇 |
2018年 | 11篇 |
2017年 | 14篇 |
2016年 | 16篇 |
2015年 | 10篇 |
2014年 | 17篇 |
2013年 | 41篇 |
2012年 | 26篇 |
2011年 | 43篇 |
2010年 | 36篇 |
2009年 | 26篇 |
2008年 | 31篇 |
2007年 | 31篇 |
2006年 | 34篇 |
2005年 | 19篇 |
2004年 | 22篇 |
2003年 | 16篇 |
2002年 | 14篇 |
2001年 | 17篇 |
2000年 | 12篇 |
1999年 | 13篇 |
1998年 | 60篇 |
1997年 | 27篇 |
1996年 | 19篇 |
1995年 | 14篇 |
1994年 | 18篇 |
1993年 | 25篇 |
1992年 | 10篇 |
1991年 | 8篇 |
1990年 | 15篇 |
1989年 | 12篇 |
1988年 | 10篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 10篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 11篇 |
1978年 | 5篇 |
1977年 | 10篇 |
1976年 | 11篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1963年 | 3篇 |
排序方式: 共有843条查询结果,搜索用时 15 毫秒
61.
Rex T. McMahon Robert W. Blake C. Richard Shumway David J. Leatham Michael A. Tomaszewski Kenneth R. Butcher 《Journal of dairy science》1985,68(9):2295-2302
Net present values of semen were calculated for alternative generations of descendants in the planning horizon, conception rate to first service, and selection policy for milk income and type score for retail semen prices and real interest 3%. Data were active Holstein and Jersey artificial insemination sires whose semen was available for purchase after the January 1984 USDA Sire Summary. Objectives were to determine effects of length of planning horizon and conception rate on rankings of sires for profit.Two generations (daughter and granddaughter) for Holstein and one generation of descendants for Jersey sires were sufficiently long planning periods, because sires ranked nearly the same (rank correlation >.99) with longer horizons. Misspecification of conception rate (largest cost), planning horizon, or both reduced profitability of sire selection by .4 to 1.2 standard deviations of net present value. Because of modest semen prices of most profitable sires, the largest cost of inefficient sire selection by inaccurate specification of conception rate and planning horizon is the opportunity loss of future net income. Interaction of optimal sire selection with herd management is analogous to interaction of genotype by environment for profit. 相似文献
62.
Raffrenato E Blake RW Oltenacu PA Carvalheira J Licitra G 《Journal of dairy science》2003,86(7):2470-2479
Differential genetic expression in high and low opportunity Sicilian Holstein-Friesian and Brown Swiss herd environments was investigated using endogenous and exogenous variables in a set of three definitions. Results of genetic by environmental interaction were compared using alternative environmental definitions: within herd-year standard deviation for mature equivalent milk yield (HYSD), detectable incidence of normal vs. abnormal (peakless) lactation and herds clustered by causal relationships from high and low frequency use of nutrition, milking, health and animal handling practices. Data for genetic analysis consisted of first-lactation standardized yields of milk, fat and protein, and weighted somatic cell score for 8897 daughters of 825 Holstein-Friesian sires and 1143 daughters of 220 Brown Swiss sires. Components of covariance, heritabilities, and genetic correlations were estimated using bivariate and multivariate sire models for average and contrasting environments for each definition. Sire variances for yields were consistently smaller in the low opportunity environments of both breeds. Except for differential incidence of abnormal lactation in Friesian herds, correlated yield response in less privileged environments was 0.41 to 0.81 as much as in high opportunity environments, a substantial loss. Genetic correlations between HYSD environments for yield traits of Friesian were 0.48 to 0.66 but exceeded 0.80 for other definitions. Less correlated response in somatic cell score was also predicted for environments with low use of yield-enhancing practices (0.66 for Friesian and 0.61 for Brown Swiss), which may have resulted from less health care and poorer milking management. Therefore, unfavorable management interactions likely foster unequal gains from selection in contrasting environments defined exogenously or by incidence of peakless lactation. Conversely, greater genetic as well as phenotypic response is expected from additional inputs of nutrition, health care and milking management. 相似文献
63.
芬美意公司的AFFIRM技术 总被引:1,自引:0,他引:1
Anthony Blake 《中国食品工业》2003,(3):48-49
当进食时,食物会释放出挥发性的气味分子,然后通过呼吸进入嗅觉器官.嗅觉器官位于鼻子的上方及眼睛的后面.我们嘴里感觉到的触觉和味觉是和嗅觉信号紧密相关的,我们通常把这三种感觉同时存在时的感受称作味道.其中嗅觉是能使我们鉴别食物感觉的最重要的一种,这也是我们在鼻子塞住后很难鉴别食物味道的原因(比如感冒时).在进食时,我们当然可以不断地闻到食物的味道,因此我们把嗅觉定义为一种能随时间而改变的感觉. 相似文献
64.
This paper presents the results of an experimental study to measure professionalism for the purpose of assessing a professional development program. Soft skills such as professionalism are increasingly recognized as important, yet measuring and assessing these skills, typically best acquired experientially, has remained challenging. Following established research, we conceptualize professionalism as a construct with the dimensions of autonomy, commitment, belief in public service, self-regulation, and the use of a professional organization as a major referent. We demonstrate how these dimensions can be expressed and the professionalism of free-form text responses measured. These responses are reflections submitted online by participants in a professional development program for undergraduate business majors known as the Management Achievement Program (MAP). Latent semantic analysis is employed to measure the professionalism of these responses and to assess MAP along each of the five dimensions. The method demonstrated in this paper has several advantages over existing methods for assessment, which can be costly, require considerable time and training, and are often tied to subjective interpretation. The method demonstrated here is suitable for replication that leads to continuous improvement by “closing the loop.” 相似文献
65.
The emerging discipline of Landscape Ecology is described, and its historical development studied. Differences between European and North American practice are revealed and the discipline is seen to emerge as much from ecological studies as from geography, forestry and landscape architecture. An extensive list of references is given. 相似文献
68.
S. Kutti Rani S. Nirmal Kumar Crystal Y. Wilson A. Gopi D. Easwaramoorthy 《Journal of Industrial and Engineering Chemistry》2009,15(6):898-901
The oxidation of vanillin by peroxomonosulphate (PMS) in acetic acid–sodium acetate buffered medium was carried out at 308 K. The rate was first order with respect to [vanillin] and [PMS]. The rate increased with increase in pH and the rate was too fast to be measured at pH 5.2. The rate increased with increase in [acetate] and the plot of kobs versus [acetate] was a straight line with positive intercept. Variation of ionic strength had no effect on the rate of the reaction. Effects of polarity were studied with five different solvents and in all the cases, log kobs versus 1/? were linear with negative slope. The reaction had been carried out at four different temperatures and the activation and thermodynamic parameters were calculated. The product of oxidation was confirmed as vanillic acid by IR, 1H NMR and GC-MS spectral analysis. Based on the results obtained a reaction scheme had been proposed and the rate law was derived. 相似文献
69.
Interest in meaning and meaning making in the context of stressful life events continues to grow, but research is hampered by conceptual and methodological limitations. Drawing on current theories, the author first presents an integrated model of meaning making. This model distinguishes between the constructs of global and situational meaning and between “meaning-making efforts” and “meaning made,” and it elaborates subconstructs within these constructs. Using this model, the author reviews the empirical research regarding meaning in the context of adjustment to stressful events, outlining what has been established to date and evaluating the strengths and weaknesses of current empirical work. Results suggest that theory on meaning and meaning making has developed apace, but empirical research has failed to keep up with these developments, creating a significant gap between the rich but abstract theories and empirical tests of them. Given current empirical findings, some aspects of the meaning-making model appear to be well supported but others are not, and the quality of meaning-making efforts and meanings made may be at least as important as their quantity. This article concludes with specific suggestions for future research. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
70.
Tina Tin Benjamin K. Sovacool David Blake Peter Magill Saad El Naggar Sven Lidstrom Kenji Ishizawa Johan Berte 《Renewable Energy》2010,35(8):1715-1723
This article showcases a range of small and large scale energy efficiency and renewable energy deployments at Antarctic research stations and field camps. Due to the cold and harsh environment, significant amounts of fuel are needed to support humans working and living in Antarctica. The purchase, transportation and storage of large amounts of fossil fuel entail significant economic costs and environmental risks and have motivated developments in energy efficiency and renewable energy deployment. Over the past three decades, improved building design, behavioral change, cogeneration, solar collectors, solar panels and wind turbines have been found to be effective in Antarctica, demonstrating that harsh environmental conditions and technological barriers do not have to limit the deployment of energy efficiency and renewable energy. The ambition to run entire stations or field camps on 100% renewable energy is increasingly common and feasible. While the power requirements of Antarctic research stations are small compared to urban installations on other continents, these case studies clearly demonstrate that if energy efficiency and renewable energy can be deployed widely on the coldest, darkest and most remote continent of the world, their deployment should be more widespread and encouraged on other continents. 相似文献