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   306篇
  免费   5篇
电工技术   17篇
化学工业   43篇
金属工艺   6篇
机械仪表   1篇
建筑科学   21篇
能源动力   21篇
轻工业   34篇
水利工程   5篇
石油天然气   1篇
无线电   39篇
一般工业技术   44篇
冶金工业   14篇
原子能技术   2篇
自动化技术   63篇
  2023年   1篇
  2022年   9篇
  2021年   7篇
  2020年   5篇
  2019年   9篇
  2018年   7篇
  2017年   6篇
  2016年   5篇
  2015年   7篇
  2014年   10篇
  2013年   20篇
  2012年   16篇
  2011年   25篇
  2010年   15篇
  2009年   24篇
  2008年   27篇
  2007年   21篇
  2006年   18篇
  2005年   6篇
  2004年   12篇
  2003年   8篇
  2002年   8篇
  2001年   5篇
  2000年   3篇
  1999年   4篇
  1998年   9篇
  1997年   8篇
  1996年   3篇
  1995年   2篇
  1990年   1篇
  1989年   2篇
  1986年   1篇
  1985年   1篇
  1984年   1篇
  1980年   1篇
  1977年   1篇
  1974年   1篇
  1973年   1篇
  1971年   1篇
排序方式: 共有311条查询结果,搜索用时 0 毫秒
21.
The reduction of CO2 emissions and fuel consumption from road transportation constitutes an important pillar of the European Union strategy for implementing the Kyoto Protocol. The commitment to reduce passenger car average CO2 emissions at 140 g/km in 2008 signed by European car manufacturers and the European Commission is up to now the most important initiative towards limiting CO2 emissions from road transportation and particularly from passenger cars. Until today, annual reports show the manufacturers’ efforts in limiting CO2 emissions is within the intermediate target set by the commitment and these results are incorporated in emissions estimations and scientific studies. This paper analyses the origin of the progress achieved so far in CO2 emissions and attempts an assessment of the commitment using independent experimental emission data. Additionally, the applicability of the commitment-monitoring data into policy and decision-making tools is being examined. The results indicate that a significant part of the reductions achieved so far is due to a market shift towards diesel vehicle sales and that no reduction factors should be applied yet in CO2 emissions estimation models.  相似文献   
22.
Plug-in hybrid electric vehicle (PHEV) technology is receiving attention as an approach to reducing US dependency on foreign oil and greenhouse gas (GHG) emissions from the transportation sector. PHEVs require large batteries for energy storage, which affect vehicle cost, weight, and performance. We construct PHEV simulation models to account for the effects of additional batteries on fuel consumption, cost, and GHG emissions over a range of charging frequencies (distance traveled between charges). We find that when charged frequently, every 20 miles or less, using average US electricity, small-capacity PHEVs are less expensive and release fewer GHGs than hybrid electric vehicles (HEVs) or conventional vehicles. For moderate charging intervals of 20–100 miles, PHEVs release fewer GHGs, but HEVs have lower lifetime costs. High fuel prices, low-cost batteries, or high carbon taxes combined with low-carbon electricity generation would make small-capacity PHEVs cost competitive for a wide range of drivers. In contrast, increased battery specific energy or carbon taxes without decarbonization of the electricity grid would have limited impact. Large-capacity PHEVs sized for 40 or more miles of electric-only travel do not offer the lowest lifetime cost in any scenario, although they could minimize GHG emissions for some drivers and provide potential to shift air pollutant emissions away from population centers. The tradeoffs identified in this analysis can provide a space for vehicle manufacturers, policymakers, and the public to identify optimal decisions for PHEV design, policy and use. Given the alignment of economic, environmental, and national security objectives, policies aimed at putting PHEVs on the road will likely be most effective if they focus on adoption of small-capacity PHEVs by urban drivers who can charge frequently.  相似文献   
23.
Intermittent agitation strategies have been increasingly used for a range of process development applications, i.e., to modulate physical cues, to improve stem cell differentiation yields, and to control hydrodynamic shear stresses in microcarrier suspension; however, there is a distinct lack of characterization. Both continuous and intermittent agitation modes in relation to suspension and mixing dynamics within a DASGIP bioreactor were characterized. Suspension dynamics were found to be affected by microcarrier porosity and the degree of settling was found to be more pronounced at the top of the bioreactor. Mixing time characterization showed a marked improvement in mixing efficiency for intermittent agitation, with an overall dependence on the timing of tracer insertion.  相似文献   
24.
Industrial facilities are becoming more and more dependent on computer control of their processes, and as a consequence, require an increase in cleanliness and reliability of the electrical power supply system. Electromechanical subsystems are being replaced by electronic logic. Harmonic interference, welding, variable speed drives, and other "in plant" noise have reliable mitigation procedures. However, lightning and other external sourced power disturbances rank high on the list of "uncontrollable" events that have shut down facilities in recent years. This paper provides an overview of the causes of power-line surges and their consequences for an industrial plant. The relevant international surge-protection standards will be briefly reviewed, and their differences will be analyzed. Different technologies utilized in the implementation of various commercially available surge-protection devices will be presented, followed by a comparative analysis. Finally, the latest trends and the most promising technologies in surge-protection systems as well as their ability to overcome the problems associated with conventional protection devices will be overviewed, and experimental data based on field trials are reported  相似文献   
25.
Samaras  K. 《Electronics letters》1999,35(25):2174-2176
A novel multiple access protocol suitable for packet voice transmission over TDMA-based wireless networks is introduced. The protocol, called the polling assisted by reservations (PAR), is a combination of cyclic polling with random access. Simulation results are provided demonstrating that the PAR protocol offers a significant performance improvement over cyclic polling schemes  相似文献   
26.
Fe-Co bimetallic catalysts supported on MgO were studied for the catalytic chemical vapor deposition growth of carbon nanotubes (CNTs). Different wt.% metal loadings were investigated at various deposition temperatures and times. Characterization of the products involved thermal analysis (DTA-TGA), X-ray diffraction, spectroscopy (Raman, UPS, EELS and STS) and microscopy (SEM, TEM and STM) techniques. It was found that the metal content is critical, not only to the yield and the structural quality of the synthesized carbon nanotubes, but it can be also used to tune the desired type of synthesized nanotubes. Lower (2 wt.%) loadings of Fe-Co catalysts favor the formation of single- and/or double-wall CNTs for deposition time and temperature 30 min and 800 °C, respectively. Thermal analysis and Raman measurements showed that these thin CNTs were synthesized at high amounts (CNT-per-catalyst wt.% of more than 100%), exhibiting high graphitization degree with only traces of by-products (mainly amorphous carbon) among them. Microscopy results revealed the formation of CNTs bundles, consisting of individual nanotubes with less than 2 nm outer diameter, while additional energy loss measurements pointed out that the deposited CNTs are mainly single wall. Higher (10 wt.%) Fe-Co loadings resulted to the formation of multi-wall CNTs.  相似文献   
27.
Chronic kidney disease (CKD) is an important global public health problem due to its high prevalence and morbidity. Although the treatment of nephrology patients has changed considerably, ineffectiveness and side effects of medications represent a major issue. In an effort to elucidate the contribution of genetic variants located in several genes in the response to treatment of patients with CKD, we performed a systematic review and meta-analysis of all available pharmacogenetics studies. The association between genotype distribution and response to medication was examined using the dominant, recessive, and additive inheritance models. Subgroup analysis based on ethnicity was also performed. In total, 29 studies were included in the meta-analysis, which examined the association of 11 genes (16 polymorphisms) with the response to treatment regarding CKD. Among the 29 studies, 18 studies included patients with renal transplantation, 8 involved patients with nephrotic syndrome, and 3 studies included patients with lupus nephritis. The present meta-analysis provides strong evidence for the contribution of variants harbored in the ABCB1, IL-10, ITPA, MIF, and TNF genes that creates some genetic predisposition that reduces effectiveness or is associated with adverse events of medications used in CKD.  相似文献   
28.
Prostaglandin E2 (PGE2) is known to increase glioblastoma (GBM) cell proliferation and migration while cyclooxygenase (COX) inhibition decreases proliferation and migration. The present study investigated the effects of COX inhibitors and PGE2 receptor antagonists on GBM cell biology. Cells were grown with inhibitors and dose response, viable cell counting, flow cytometry, cell migration, gene expression, Western blotting, and gelatin zymography studies were performed. The stimulatory effects of PGE2 and the inhibitory effects of ibuprofen (IBP) were confirmed in GBM cells. The EP2 and EP4 receptors were identified as important mediators of the actions of PGE2 in GBM cells. The concomitant inhibition of EP2 and EP4 caused a significant decrease in cell migration which was not reverted by exogenous PGE2. In T98G cells exogenous PGE2 increased latent MMP2 gelatinolytic activity. The inhibition of COX1 or COX2 caused significant alterations in MMP2 expression and gelatinolytic activity in GBM cells. These findings provide further evidence for the importance of PGE2 signalling through the EP2 and the EP4 receptor in the control of GBM cell biology. They also support the hypothesis that a relationship exists between COX1 and MMP2 in GBM cells which merits further investigation as a novel therapeutic target for drug development.  相似文献   
29.
The scope of this paper is to summarise a methodology developed for TRENDS (TRansport and ENvironment Database System-TRENDS). The main objective of TRENDS was the calculation of environmental pressure indicators caused by transport. The environmental pressures considered are associated with air emissions from the four main transport modes, i.e. road, rail, ships and air. In order to determine these indicators a system for calculating a range of environmental pressures due to transport was developed within a PC-based MS Access environment. Emphasis is given on the latest features incorporated in the model and their applications. One of the recently developed features of the software provides an option for simple scenario analysis including vehicle dynamics (such as turnover and evolution) for all EU15 member states. This feature is called the Transport Activity Balance module (TAB) and enables the production of collective results for all transport modes as well as a comparative assessment of air emissions produced by the various modes. Traffic activity and emission data obtained according to a basic (reference) scenario are displayed for the time period 1970-2020. In addition, a detailed assessment of the results produced by TRENDS was conducted by means of comparison with data found in the literature. Finally, vehicle emissions produced by the model for the EU15 member states were spatially disaggregated for the base year, 1995 and GIS maps were generated. Examples of these maps are displayed in this document, for the various modes of transport considered in the study.  相似文献   
30.
In this paper we provide an assessment of the water–energy nexus for Greece. More specifically, the amount of freshwater consumed per unit of energy produced is determined: for both conventional (lignite, diesel and fuel oil-fired) and advanced (combined operation of gas turbine) thermal power plants in the electricity generation sector; for extraction and refining activities in the primary energy production sector; and for the production of biodiesel that is used as a blend in the ultimately delivered automotive diesel fuel. In addition, the amount of electricity consumed for the purposes of water supply and sewerage is presented. In view of the expected effects of climate change in the Mediterranean region, the results of this study highlight the need for authorities to prepare a national strategy that will ensure climate resilience in both energy and water sectors of the country.  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