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   18519篇
  免费   844篇
  国内免费   600篇
电工技术   4122篇
技术理论   9篇
综合类   2745篇
化学工业   2958篇
金属工艺   241篇
机械仪表   349篇
建筑科学   2298篇
矿业工程   947篇
能源动力   1290篇
轻工业   1014篇
水利工程   524篇
石油天然气   543篇
武器工业   9篇
无线电   495篇
一般工业技术   631篇
冶金工业   973篇
原子能技术   25篇
自动化技术   790篇
  2024年   24篇
  2023年   163篇
  2022年   275篇
  2021年   405篇
  2020年   409篇
  2019年   262篇
  2018年   211篇
  2017年   230篇
  2016年   288篇
  2015年   292篇
  2014年   810篇
  2013年   627篇
  2012年   959篇
  2011年   1180篇
  2010年   1104篇
  2009年   1123篇
  2008年   1030篇
  2007年   1542篇
  2006年   1506篇
  2005年   1350篇
  2004年   1223篇
  2003年   1173篇
  2002年   880篇
  2001年   775篇
  2000年   646篇
  1999年   484篇
  1998年   292篇
  1997年   188篇
  1996年   129篇
  1995年   119篇
  1994年   102篇
  1993年   47篇
  1992年   30篇
  1991年   19篇
  1990年   11篇
  1989年   11篇
  1988年   8篇
  1987年   2篇
  1986年   4篇
  1985年   7篇
  1984年   6篇
  1977年   1篇
  1975年   1篇
  1974年   1篇
  1972年   1篇
  1971年   2篇
  1970年   2篇
  1964年   1篇
  1955年   2篇
  1954年   1篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
The effects of a rural roads programme depend on labour mobility, how the programme is financed, and agglomeration economies. If financed by a rural poll tax and cross-price effects and agglomeration economies are sufficiently small, the wage will rise, with some return migration. Taxes on trade act as countervailing distortions, yielding urban households some relief. Rural-urban commuting promotes the exploitation of agglomeration economies; taxes on international trade are then inferior to a poll tax. The change in the value, at producer prices, of the rural sector's net supply vector can be a poor measure of the programme's social profitability.  相似文献   
2.
空气源热泵结霜过程会恶化机组的实际运行性能,重霜工况下尤为严重,发展抑霜型空气源热泵是保障其高效适用和良性发展的关键。本文依托四川省康定市的某住宅示范工程,开展抑霜型空气源热泵和常规型空气源热泵的现场实测研究,研究抑霜型空气源热泵实际应用中的抑霜、制热性能表现,并进行技术经济性分析。结果表明:抑霜型空气源热泵抑霜效果显著,制热性能得到显著改善,能效提升达到21%~37.3%,费用年值比常规空气源热泵降低了13%,1年左右即可回收追加的投资,具有更好的技术经济性,有助于空气源热泵技术在严重结霜气候区域的高效应用。  相似文献   
3.
This study was conducted to estimate the potential for green H2 in Paraguay. A total production potential of 22.5 × 106 tons/year was obtained with a main contribution (93.34%) from solar photovoltaic. The greatest potential for producing H2 from solar and wind resources is in the Western region, and from hydro resources is in the Eastern region of the country. Two end-uses of green H2 were assessed: (1) automotive transportation, replacing gasoline and diesel; and (2) residential energy, replacing firewood and LPG for cooking in households across the country. In 16 of the 17 departments, green H2 is able to replace the overall consumption of gasoline and diesel, as well as firewood and LPG. Finally, energy service cost (mobility), environmental aspects and CO2 emissions were considered for three urban mobility technologies for the Metropolitan Area of Asunción. Results show that the mobility cost of fuel cell hybrid electric buses is still very high in comparison to diesel buses and battery electric buses. However, when a longer driving range is required, fuel cell hybrid electric buses could become a viable alternative in the long term. From an environmental point of view, green H2 used in fuel cell hybrid electric buses has the potential to save about 96% of CO2 emissions in comparison to diesel buses. It is concluded that the estimated green H2 production potential favors the incorporation of the Hydrogen Economy in Paraguay.  相似文献   
4.
Within a circular economy approach, this study investigates the environmental impact of lightweight aggregates (LWAs) produced starting from different mixes of different clays with brewery sludge and cattle bone flour ash (CBA), used as poring and fertilizing agents, respectively. The environmental impact was evaluated by means of release tests, insulation capacity, carbon footprint (CFP), and particulate matter emission during pellet firing. Release tests representative of LWAs realistic application showed very high release of phosphate and satisfactory release of potassium. The thermal insulation of the LWAs was tested by thermal imaging camera and resulted highly variable depending on the composition, with the mix containing CBA performing best. This latter composition leads also to the smallest CO2 equivalent emission, due to the calorific power of CBA, allowing lower consumption of fossil fuels during the LWA production. Finally, total particulate emissions during the thermal treatment resulted similar in terms of mass for all mixes, while differences in terms of particle morphology and composition occurred. Samples containing residue resulted with a quite good release behavior, CFP, and insulation properties, but higher emission of particles, particularly when glass is added.  相似文献   
5.
6.
Improvements in information and communications technologies (ICTs) have facilitated the inclusion of the sharing economy (SE) in societies more than ever. In the aftermath of recent disasters, the SE played significant roles to help the affected people and support official responders. However, the literature has not effectively explored these roles, and thus, no framework can support the systematic inclusion of the SE in disasters management. This paper aims to address the gap through a two-stage exploratory research approach. First, we conduct a systematic literature review to identify the extent to which the SE is taken into consideration in disasters. After that, we investigate the role of three Iranian SE-based companies that were involved in the 2019 Iran floods response. We collect empirical data by conducting semi-structured interviews and reviewing official reports.Our findings indicate that very few studies discuss the different roles of the SE in disasters, although SE companies have often provided effective solutions to address critical post-disaster logistics challenges. Four research propositions are presented to describe emerging roles for SE companies. The contribution of our study is twofold. First, our research identifies the different roles that the SE could play in disasters and therefore, brings a new perspective to the literature. Second, the study suggests opportunities for collaboration and partnership models from the point of origin to delivery that can support coordination and logistics in disasters.  相似文献   
7.
中国天然气市场可持续发展分析   总被引:1,自引:0,他引:1  
杨建红 《天然气工业》2018,38(4):145-152
承接2016年回暖之势,2017年中国天然气市场迎来爆发式增长,全年天然气消费量达2 335×10~8 m~3、年消费增量达353×10~8 m~3。为此,有必要剖析推动中国天然气市场爆发式增长的主要因素并预测其未来发展的可持续性。研究结果表明:(1)2017年爆发式增长主要受益于宏观经济形势好转、大气污染防治措施深入实施、化工等大宗产品价格回升、华东地区天然气发电负荷增加、管道天然气供应价格相对较低、LNG汽车市场整体呈现回暖态势等因素;(2)经济发展形势、"煤改气"的推进、政策实施方向、油气价格趋势等外部因素将能继续支持天然气市场的快速增长;(3)但天然气产业的自身条件、资源和基础设施条件将对市场发展造成制约。结论认为:(1)2020年之前我国天然气市场需求量仍会保持快速增长的趋势,但难以维持每年300×10~8 m~3的增长规模;(2)工业燃料和发电是天然气市场发展的主要方向;(3)环渤海等地区是未来天然气需求量增长的主要区域。为了保持我国天然气市场的发展态势,提出如下建议:(1)千方百计扩大天然气供应规模,在认真做好国产非常规天然气资源开发的同时,积极落实进口天然气资源;(2)毫不松懈地建设基础设施,管道要超前建设,LNG接收站要加大力度建设,地下储气库等调峰设施要鼓励建设;(3)科学合理地理顺天然气价格,居民价格与非居民价格并轨首当其冲,确立价格是平衡供需关系的杠杆作用,减少行政干涉。  相似文献   
8.
ABSTRACT

Supply chains are becoming increasingly complex, and many companies and researchers are looking to nature for finding solutions. In this paper, we provide a narrative synthesis and systematic review to explore state-of-the-art, and identify key areas for exploration of nature inspired solutions in the supply chain area. We consider strategic, tactical, and operational decisions within supply chains and identify analogies between biological systems and supply chains to create a new research agenda. Our findings show that the majority of the research in nature inspired supply chains from the systemic perspective focuses on closed loop supply chains. In contrast, similar systemic solutions such as industrial symbiosis, circular economy, and industrial ecology have not been explored as frequently. Reducing production waste (industrial symbiosis) in addition to end-of-life product waste (closed loop supply chains), optimising raw material use and extending the life of used resources (circular economy), investigating the interactions between biosphere and technosphere (industrial ecology), and seeking solutions to industrial problems from nature (biomimicry) are all possible paths for reaching a zero-waste economy. These systemic solutions have a considerable impact on the supply chains at the strategic, tactical, and operational levels, which need to be explored to identify efficient and effective solutions.  相似文献   
9.
黑龙江是我国最大的大豆优势产区,研究其大豆产业高质量发展的思路和有效路径,对于振兴我国国产大豆产业,推动供给侧改革,助力乡村振兴战略,促进地方产业经济发展,保障粮食安全具有重要意义。通过对黑龙江大豆产业现状和海伦大豆产业优势进行分析,结合国家重大产业政策导向,提出以海伦大豆为例,基于供应链、产业链、价值链“三链协同”的黑龙江大豆产业高质量发展思路,为推进“十四五”时期我国国产大豆产业发展提供参考。  相似文献   
10.
陈丽 《食品与机械》2018,34(3):86-88,122
由于网络订餐运营模式同传统餐饮行业的较大差异,现行《食品安全法》对其食品安全进行了专门的规定。然而,由于网络订餐出现的时间不长,其依然存在行政监管缺位、第三方平台缺乏必要的食品安全审核和管理机制、消费者缺乏食品安全意识等食品安全隐患。有必要采取建立以食品药品监督管理机关为主的监管体系、加强第三方平台的自律管理、确立第三方平台的食品安全提示义务等法律规制措施,才能保证网络订餐的正常健康发展。  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