首页 | 官方网站   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   853篇
  免费   30篇
工业技术   883篇
  2023年   5篇
  2022年   31篇
  2021年   30篇
  2020年   15篇
  2019年   5篇
  2018年   14篇
  2017年   14篇
  2016年   24篇
  2015年   16篇
  2014年   22篇
  2013年   58篇
  2012年   38篇
  2011年   38篇
  2010年   34篇
  2009年   31篇
  2008年   44篇
  2007年   41篇
  2006年   33篇
  2005年   25篇
  2004年   25篇
  2003年   16篇
  2002年   25篇
  2001年   13篇
  2000年   7篇
  1999年   13篇
  1998年   23篇
  1997年   18篇
  1996年   20篇
  1995年   9篇
  1994年   20篇
  1993年   13篇
  1992年   14篇
  1990年   10篇
  1989年   12篇
  1988年   7篇
  1987年   11篇
  1986年   7篇
  1985年   11篇
  1984年   6篇
  1983年   6篇
  1981年   8篇
  1980年   5篇
  1979年   6篇
  1978年   5篇
  1977年   7篇
  1975年   9篇
  1974年   6篇
  1972年   5篇
  1968年   3篇
  1966年   4篇
排序方式: 共有883条查询结果,搜索用时 15 毫秒
1.
This paper assesses the impacts of a GTL plant on the expansion of Brazil's oil refining segment. The GTL plant (50,000 bpd) was sized to start up operations in 2015, producing diesel and naphtha through the indirect route (FT-synthesis). This plant will consume the non-associated natural gas production from the recent discoveries at the Santos Basin (around 419 Bm3), and the associated gas production from the Campos Basin. Both basins are located in the Southeast of Brazil, the most populated, rich and industrialized region of the country. Two different criteria for refinery expansion were simulated in order to meet oil product demand scenarios. Findings show that depending on the refinery expansion criteria considered GTL will play a fundamental hole to meet the oil product demand forecast to Brazil in the next 10 years.  相似文献   
2.
With the increasing use of electric motors in automobiles—in some cases as many as 100 electric motors per vehicle—alternatives to ferrite magnetic materials are under consideration. If more powerful magnetic materials could be implemented, size reductions in these motors could result in curb weight reductions that lead to improved fuel economy. NdFeB magnets are attractive as potential replacement materials, due to their higher flux density and thus smaller required size; however, high material costs have limited their implementation. To investigate the economic competitiveness of alternative magnetic materials, technical cost models (TCMs) were developed and used to examine the manufacturing economics related to the production of both NdFeB and ferrite magnets. Results from the TCMs are used to identify the cost drivers and opportunities for cost reductions. Subsequent investigations will include effects on vehicle fuel efficiency, and the environmental impact of magnet manufacture and disposal.  相似文献   
3.
A national effort, begun in 1972 to increase the numbers of minorities in engineering, has made substantial progress, but the attrition for minority students is still estimated at 70%. To address the problem, Project Preserve was designed to confirm, by demonstration, the results of previous research showing that the combination of explicit cognitive development, close relationships with faculty, and strong bonds to an institution can raise the performance and retention of minority engineering students. The project enrolled over 100 minority engineering students who had been dismissed from freshman engineering studies on other campuses or placed on academic probation, but whose high school grades and SAT scores were indicative of success. They were channeled into participating institutions chosen for their record of basic support services, willingness to augment or restructure those services, and for variation among institutional variables: Xavier University of Louisiana (XU), California State University at Northridge (CSUN), and City College of the City University of New York (CCNY). A 2 1/2 hour battery of evaluation instruments was given to 79 students upon entry and to 26 students upon their attaining Junior status after two years in the program. The results demonstrated that: (1) an admirable 64% of would-be drop outs had achieved Junior status or were still enrolled in engineering at the conclusion of two years; (2) cognitive growth occurred on basic memory skills and one critical thinking skill, but there were institutional differences in the extent of intellectual development, with Xavier producing the most change; (3) closer relationships to faculty were outcomes; (4) the most positive feelings about, or bonding to, the institution occurred at Xavier University, while the most evidence of social participation and connectedness occurred at CSUN.  相似文献   
4.
As life expectancy has increased, particularly in developed countries, due to medical advances and increased prosperity, age-related neurological diseases and mental health disorders have become more prevalent health issues, reducing the well-being and quality of life of sufferers and their families. In recent decades, due to reduced work-related levels of physical activity, and key research insights, prescribing adequate exercise has become an innovative strategy to prevent or delay the onset of these pathologies and has been demonstrated to have therapeutic benefits when used as a sole or combination treatment. Recent evidence suggests that the beneficial effects of exercise on the brain are related to several underlying mechanisms related to muscle–brain, liver–brain and gut–brain crosstalk. Therefore, this review aims to summarize the most relevant current knowledge of the impact of exercise on mood disorders and neurodegenerative diseases, and to highlight the established and potential underlying mechanisms involved in exercise–brain communication and their benefits for physiology and brain function.  相似文献   
5.
The combined erosion-oxidation of nickel, cobalt, and the oxides of these metals have been studied at 780°C in air to examine two regimes of interactionnamely, a regime of erosion-enhanced oxidation during which an oxide scale of constant thickness covers metal specimens, and a regime of oxidation-affected erosion that is characterized by a composite surface layer of metal, oxide, and erodent. In the case of cobalt, these two regimes have been documented and the transition from one regime to another described. For the range of conditions examined, only the oxidation-affected erosion regime was observed for nickel due to its lower oxidation rate compared to cobalt.  相似文献   
6.
Obesity and its associated disorders are a growing epidemic across the world. Many genetic, physiological, and behavioral factors play a role in the etiology of obesity. Diet and exercise are known to play a valuable role in the treatment and prevention of obesity and associated disorders such as hypertension, heart disease, and diabetes. Therefore, the purpose of this review is to examine the prevalence, etiology, consequences, and treatment of obesity.  相似文献   
7.
The modes of interaction of erosion and high-temperature oxidation, occurring simultaneously on an alloy surface, have been studied using Ni-30Cr, MA754, Ni-20Al, and Co-22Cr-11Al-0.2Y alloys to examine the influence of chromia and alumina scale formation on the erosion of nickel and cobalt base alloys. The results have shown that, in the presence of a rapidly flowing oxidizing gas stream, the evaporation of volatile metal oxides becomes important at lower temperatures where normally it can be ignored. Otherwise, the erosion and oxidation of alloys parallels the behavior of pure metals but also introduces additional factors derived from lengthening of the period of transient oxidation and modification of concentration profiles in the alloy adjacent to the alloy/scale interface. Higher erosion intensities extend the transient oxidation behavior which adversely affects the formation of protective scales. As with pure metals, the presence of erosion and oxidation together always produced increased rates of degradation.  相似文献   
8.
Multilayer hybrid visualizations to support 3D GIS   总被引:3,自引:0,他引:3  
In this paper, we present a unique hybrid visualization system for spatial data. Although some existing 3D GIS systems offer 2D views they are typically isolated from the 3D view in that they are presented in a separate window. Our system is a novel hybrid 2D/3D approach that seamlessly integrates 2D and 3D views of the same data. In our interface, multiple layers of information are continuously transformed between the 2D and 3D modes under the control of the user, directly over a base terrain. In this way, our prototype system is able to depict 2D and 3D views within the same window. This has advantages, since 2D and 3D visualizations can each be easier to interpret in different contexts.In this work we develop this concept of a hybrid visualization by presenting a comprehensive set of capabilities within our distinctive system. These include new facilities such as: hybrid landmark, 3D point, and chart layers, the grouping of multiple hybrid layers, layer painting, the merging of layer controls and consistent zooming functionality.  相似文献   
9.
Given the prevalence of computers in education today, it is critical to understand teachers’ perspectives regarding computer integration in their classrooms. The current study surveyed a random sample of a heterogeneous group of 185 elementary and 204 secondary teachers in order to provide a comprehensive summary of teacher characteristics and variables that best discriminate between teachers who integrate computers and those who do not. Discriminant Function Analysis indicated seven variables for elementary teachers and six for secondary teachers (accounting for 74% and 68% of the variance, respectively) that discriminated between high and low integrators. Variables included positive teaching experiences with computers; teacher’s comfort with computers; beliefs supporting the use of computers as an instructional tool; training; motivation; support; and teaching efficacy. Implications for support of computer integration in the classroom are discussed.  相似文献   
10.
Value in the British National Health Service have shifted away from patient care towards financial control. However, in the quest for efficiency, huge amounts of NHS money have been wasted on computer system which failed. In this paper, I draw on a case study to explore some of the ethical issues which underlie this kind of waste of resources. Issues include the gap between public pronouncements and personal experience, the chaos of which lies behind the facade of rationality, and the systematic silencing of people, usually women, who question the viability of computer systems which are created for private gain rather than public service.  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-23

京公网安备 11010802026262号