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   8448篇
  免费   886篇
  国内免费   411篇
电工技术   1620篇
技术理论   1篇
综合类   1284篇
化学工业   1063篇
金属工艺   96篇
机械仪表   197篇
建筑科学   1262篇
矿业工程   275篇
能源动力   584篇
轻工业   275篇
水利工程   591篇
石油天然气   226篇
武器工业   41篇
无线电   363篇
一般工业技术   582篇
冶金工业   323篇
原子能技术   16篇
自动化技术   946篇
  2024年   26篇
  2023年   182篇
  2022年   307篇
  2021年   355篇
  2020年   378篇
  2019年   302篇
  2018年   256篇
  2017年   309篇
  2016年   318篇
  2015年   329篇
  2014年   603篇
  2013年   576篇
  2012年   628篇
  2011年   622篇
  2010年   490篇
  2009年   537篇
  2008年   432篇
  2007年   588篇
  2006年   491篇
  2005年   410篇
  2004年   323篇
  2003年   292篇
  2002年   209篇
  2001年   182篇
  2000年   134篇
  1999年   108篇
  1998年   72篇
  1997年   49篇
  1996年   49篇
  1995年   33篇
  1994年   23篇
  1993年   13篇
  1992年   13篇
  1991年   12篇
  1990年   6篇
  1989年   9篇
  1988年   4篇
  1987年   8篇
  1986年   6篇
  1985年   15篇
  1984年   8篇
  1983年   15篇
  1982年   4篇
  1980年   6篇
  1962年   3篇
  1961年   1篇
  1960年   1篇
  1959年   1篇
  1957年   2篇
  1954年   1篇
排序方式: 共有9745条查询结果,搜索用时 15 毫秒
1.
The supply of electrical energy is critical to convenient and comfortable living. However, people consume a large amount of energy, contributing to an energy crisis and global warming, and damaging some ecological cycles. Residential electricity consumption has greater elasticity than industrial and business consumption; it therefore has high energy-saving potential. This work establishes an automated platform, which provides information about residential electricity consumption in each city in Taiwan. Machine learning was used to forecast future residential electricity demand. A nature-inspired optimization method was applied to enhance the accuracy of the best machine learner, yielding an even better hybrid ensemble model. Performance measures indicate that the resulting model is accurate and provides effective information for reference. An automatic web-based system based on the model was combined with a web crawler and scheduled to run automatically to provide information on monthly residential electricity consumption in each county and city. By providing energy consumption information across the country, power providers and government can discuss policy and set different goals for energy use. The results of this study can facilitate the early implementation of energy-saving and carbon emission-reducing in cities and aid utility companies in establishing energy conservation guidelines.  相似文献   
2.
《Oil and Energy Trends》2021,46(1):29-37
Current data of world oil demand. This includes international bunkers and refinery fuel. Updated on a monthly basis. Current data of oil demand from counties such as Canada, the United States of America, Japan, OECD Europe, Belgium, France, Germany, Italy, Netherlands, Spain, Sweden, the United Kingdom, Australia, Mexico, Republic of Korea, and Turkey. Updated on a monthly basis. Current data for crude oil and refined product stocks in Canada, Chile, Mexico, the United States (Western Hemisphere), France, Germany, Italy, Netherlands, Spain, the United Kingdom and Other Europe (Europe), Japan, Republic of Korea, Other Pacific (Asia‐Pacific), and Total OECD (Table 12.1) Current data for refined product stocks in the OECD Western Hemisphere, OECD Europe, OECD Asia‐Pacific and Total OECD. Products include gasoline, diesel and gasoil, and heavy fuel oil. Updated on a monthly basis (Table 12.2).  相似文献   
3.
臭氧氧化-循环喷淋法处理钨钼选矿废水   总被引:4,自引:0,他引:4  
采用臭氧氧化-循环喷淋法去除钨钼选矿废水中COD,研究了pH值、臭氧流量、循环频率对COD去除效果的影响。结果表明: 废水COD去除率随pH值、臭氧流量、循环频率增大而增加,在pH值为10、臭氧流量3.0 L/min、循环频率4.0次/min条件下,氧化120 min后废水COD含量由131 mg/L降至11.5 mg/L,COD去除率达91.2%,满足《污水综合排放标准》(GB 8978-1996)一级标准。与O2、NaClO处理废水COD的对比试验结果表明,循环喷淋法结合O3表现出较好的COD去除效果。  相似文献   
4.
We consider ex post demand information sharing in a two-echelon supply chain in which two suppliers sell differentiated products through a common retailer. We model three scenarios of information sharing to characterise the conditions under which information sharing may benefit or hurt different players: (1) no supplier is informed; (2) only one supplier is informed; and (3) both suppliers are informed. We find that the retailer may voluntarily share the low demand information when the product differentiation and demand magnitude satisfy certain conditions. In contrast, the retailer has no incentive to share the high demand information, even though this information benefits the suppliers. To achieve information sharing, we propose a side payment mechanism, which allows benefitted players to subsidise hurtful players. Finally, we extend our model by considering a situation where the suppliers have limited capacity and may invest to ramp up production capacity to satisfy a high demand.  相似文献   
5.
童长征 《橡胶科技》2020,18(2):0069-0076
2019年天然橡胶期货市场起起落落,沪胶价格继续低位震荡。2020年天然橡胶供大于求的局面仍不会发生根本性改变,由极端天气引发的天然橡胶市场行情变动可能会减小,汽车行业可能会在政策支持下再次振兴,尤其重型卡车市场会成为亮点,轮胎企业继续寻求扩大出口。2020年上半年,天然橡胶期货市场可能还会受到2019年异常天气和病害等的余波作用,胶价会达到一个相对的高点,价格底部抬升,但很难出现持续性上涨的市场行情。2020年下半年,随着天然橡胶产量的季节性增长,胶价可能会再次回落。  相似文献   
6.
将习近平总书记“精准扶贫” 的重要思想应用于高等学校教学辅导答疑工作中, 明确了高校教师辅导答疑工 作的目的、内容和措施。针对大学生在学习、生活过程中遇到的各种问题以及个性化需求, 将辅导答疑的类型分成 5 种形式, 实施精准辅导答疑, 提高人才培养质量。  相似文献   
7.
ABSTRACT

Electric heat pumps feature prominently in projected energy transitions in the UK and elsewhere. Owing to their high electricity consumption, heat pumps are viewed as important targets for demand-side response (DSR). Findings are presented from a field trial of a new control system that aims to optimize heat pump performance, including under time-varying tariff conditions. The trial involved monitoring 76 properties with heat pumps, but without dedicated heat storage; 31 of these received the control system. Interviews were conducted with a subsample of 12 participants. The controller successfully evened out electricity demand over the day (reducing the evening peak), but this was associated with increased late night and daytime temperatures. Interview participants reported some disturbance owing to overnight heating and noise, as well as usability issues with the controller interface and hardware. These issues present risks to the future acceptability of such systems. While the system delivered short-term demand reductions successfully, longer-term demand shifting risked causing unacceptable disturbance to occupants. Future control systems could overcome some of the issues identified in this pioneering trial through more effective zoning, using temperature caps or installing dedicated heat storage, but these may either limit the available flexibility or be challenging to achieve.  相似文献   
8.
Biodiesel utilization has been rapidly growing worldwide as the prime alternative to petrodiesel due to a global rise in diesel fuel demand along with hazardous emissions during its thermochemical conversion. Although, several debatable issues including feedstock availability and price, fuel and food competition, changes in land use and greenhouse gas emission have been raised by using edible as well as inedible feedstocks for the production of biodiesel. However, non-crop feedstocks could be a promising alternative. In this article, waste cooking oils have been recommended as a suitable option for biodiesel production bearing in mind the current national situation. The important factors such as the quantity of waste cooking oil produced, crude oil and vegetable oil import expenses, high-speed diesel imports, waste management issues and environmental hazards are considered. Moreover, process simulation and operating cost evaluation of an acid catalyzed biodiesel production unit are also conducted. The simulation results show that the production cost of waste cooking oil-based biodiesel is about 0.66USD·L-1. We believe that the present overview would open new pathways and ideas for the development of biofuels from waste to energy approach in Pakistan.  相似文献   
9.
《Oil and Energy Trends》2019,44(11):37-45
Current data of world oil demand. This includes international bunkers and refinery fuel. Updated on a monthly basis. Current data of oil demand from counties such as Canada, the United States of America, Japan, OECD Europe, Belgium, France, Germany, Italy, Netherlands, Spain, Sweden, the United Kingdom, Australia, Mexico, Republic of Korea, and Turkey. Updated on a monthly basis. Current data for crude oil and refined product stocks in Canada, Chile, Mexico, the United States (Western Hemisphere), France, Germany, Italy, Netherlands, Spain, the United Kingdom and Other Europe (Europe), Japan, Republic of Korea, Other Pacific (Asia-Pacific), and Total OECD (Table 12.1) Current data for refined product stocks in the OECD Western Hemisphere, OECD Europe, OECD Asia-Pacific and Total OECD. Products include gasoline, diesel and gasoil, and heavy fuel oil. Updated on a monthly basis (Table 12.2).  相似文献   
10.
The flexible operation of energy-intensive processes, such as cryogenic air separation, has economic potential due to increasing fluctuations of the electricity markets. Multiproduct air separation processes with high ratios of liquid product are very promising for flexible operation due to storable products. We present a process design with an integrated liquefication cycle and liquid assist operation, that facilitates a high liquid product ratio and a flexible process operation. We use a mechanistic dynamic process model in steady-state process optimizations covering the wide operational range of the proposed process. The optimization results show that the power demand can be varied in a range from 3.5 to 28 MW without violating operational constraints by changing the nitrogen and oxygen production rates. Thus, the proposed process is a promising air separation candidate for flexible operation with respect to fluctuating electricity markets.  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