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   2000篇
  免费   149篇
  国内免费   2篇
电工技术   14篇
综合类   14篇
化学工业   643篇
金属工艺   14篇
机械仪表   24篇
建筑科学   108篇
矿业工程   5篇
能源动力   44篇
轻工业   478篇
水利工程   21篇
石油天然气   8篇
武器工业   1篇
无线电   101篇
一般工业技术   298篇
冶金工业   132篇
原子能技术   2篇
自动化技术   244篇
  2024年   3篇
  2023年   39篇
  2022年   107篇
  2021年   141篇
  2020年   37篇
  2019年   51篇
  2018年   57篇
  2017年   65篇
  2016年   84篇
  2015年   73篇
  2014年   83篇
  2013年   153篇
  2012年   135篇
  2011年   162篇
  2010年   112篇
  2009年   105篇
  2008年   106篇
  2007年   90篇
  2006年   72篇
  2005年   66篇
  2004年   63篇
  2003年   53篇
  2002年   52篇
  2001年   19篇
  2000年   22篇
  1999年   21篇
  1998年   8篇
  1997年   8篇
  1996年   13篇
  1995年   21篇
  1994年   9篇
  1993年   8篇
  1992年   4篇
  1991年   8篇
  1990年   7篇
  1989年   10篇
  1988年   11篇
  1987年   5篇
  1986年   7篇
  1985年   5篇
  1984年   3篇
  1983年   6篇
  1982年   10篇
  1980年   3篇
  1979年   4篇
  1978年   3篇
  1975年   3篇
  1973年   3篇
  1969年   3篇
  1967年   3篇
排序方式: 共有2151条查询结果,搜索用时 15 毫秒
341.
342.
343.
Indoor air pollution from burning solid fuels for cooking is a major environmental health problem in developing countries, predominantly affecting children and women. Traditional household energy practices also contribute to substantial time loss and drudgery among households. While effective interventions exist, levels of investment to date have been very low, in part due to lack of evidence on economic viability. Between 2004 and 2007, different combinations of interventions – improved stoves, smoke hoods and a switch to liquefied petroleum gas – were implemented in poor communities in Nepal, Sudan and Kenya. The impacts were extensively evaluated and provided the basis for a household-level cost-benefit analysis, which essentially followed the methodology proposed by the World Health Organization. The results suggest that interventions are justified on economic grounds with estimated internal rates of return of 19%, 429% and 62% in Nepal, Kenya and Sudan, respectively. Time savings constituted by far the most important benefit followed by fuel cost savings; direct health improvements were a small component of the overall benefit. This paper describes the methodology applied, discusses the findings and highlights the methodological challenges that arise when a global approach is applied to a local programme.  相似文献   
344.
Ruminants are considered to be less sensitive towards mycotoxins than monogastric animals because rumen microbiota have mycotoxin‐detoxifying capacities. Therefore the effect of mycotoxins towards ruminants has been studied to a lesser extent compared with monogastric animals. Worldwide, a high proportion of the ruminant diet consists of silages made of forage crops (i.e. all parts of the crop above the stubble are harvested). In practice, silages are often contaminated with multiple mycotoxins. Exposure to a cocktail of mycotoxins can hamper animal production and have severe health consequences. In this article the different aspects associated with mycotoxin contamination of silage are reviewed ‘from seed to feed’. An overview is given on the occurrence of toxigenic fungal species and their concomitant mycotoxins in forage crops before and after ensiling. The mycotoxin load of visually non‐mouldy samples and mouldy hot spots within the same silo is also compared. Subsequently, this review delves into different problem‐solving strategies. A logical first step is prevention of mould growth and mycotoxin production in the field, during harvest and during ensiling. If prevention should fail, several remediation strategies are available. These are listed, mainly focusing on the possibilities of microbial degradation of mycotoxins in vivo in silage. © 2015 Society of Chemical Industry  相似文献   
345.
346.
In the European Union, carminic acid and its ammonium, calcium, potassium or sodium salts and its aluminium lakes are approved as food additive E120. In beverages obtained from the German market 4-aminocarminic acid (“acid-stable carmine”) was detected by HPLC–PDA and LC–MS/MS. Isolation of the colorant from a liquid dye preparation used for the production of a beverage sample and subsequent NMR analysis confirmed the presence of 4-aminocarminic acid. Synthesis of 15N-4-aminocarminic acid clearly demonstrated that “acid-stable carmine” is not the ammonium salt of carminic acid, which is approved as food additive in the European Union. In fact, nitrogen in “acid-stable carmine” is covalently bound. The molecular structure of carminic acid is chemically modified and 4-aminocarminic acid does not comply with the specifications laid down for E120 in Commission Regulation (EU) No 231/2012. 4-Aminocarminic acid was also detected in the red-colored glaze of a raspberry cake and in the liquid dye preparation used for coloring this glaze.  相似文献   
347.
Metallurgical and Materials Transactions B - The influence of filter surface chemistry on the filtration efficiency of cast aluminum alloys was evaluated for four different filter coating...  相似文献   
348.
To protect sensitive food products from oxidative deterioration, multilayer barrier film systems and also modified atmosphere packaging are widely applied. However, the preservation of food quality in such packaging systems may be compromised by the presence of defects in the sealing layer of the films, especially when these are below a critical size, typically the detection limit of standard leak testers of 10 µm. The addition of an oxygen scavenger (OS) layer in barrier film structures could therefore provide extended protection against O2 penetration through such defects. In this study, O2 absorption of different multilayer film structures including an iron‐based OS were investigated under defined gas atmospheres. Measurement cells were thereby covered with plastic films of defined O2 permeability to simulate conditions in a food package during storage with pinhole defect sizes of 10 and 17 µm. The results indicated that the OS film structures applied could only compensate for a defect size of 10 µm in the sealing layer. Analysis of the O2 absorption of different multilayer film structures at 85% and 100% relative humidity showed that higher humidity accelerates the activation of the scavenger. After full activation, the scavenger kinetics are the same for 85% and 100% relative humidity. Long‐term storage experiments using the most effective film structure from the preliminary experiments were carried out to compare O2 absorption of a snack food product in packages with and without an OS. The analyzed linear gradient of the reaction of the OS film and food product, respectively, indicated first‐order reaction kinetics with corresponding reaction constants calculated to be K (food product) 0.021 mg (O2) mbar (O2)?1 day?1 and K (OS film) 0.066 mg (O2) mbar (O2)?1 day?1. The reaction velocity of the OS was thus three times faster than that of the food. The applicability of OS multilayer film systems to compensate a critical pinhole defect size of 10 µm for sensitive food products could therefore be confirmed. The measurement of quality parameters for the status of lipid oxidation processes would help to verify this result. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
349.
Biostable fiber-reinforced composite (FRC) implants prepared from bisphenol-A-dimethacrylate and triethyleneglycoldimethacrylate resin reinforced with E-glass fibers have been successfully used in cranial reconstructions in 15 patients. Recently, porous FRC structures were suggested as potential implant materials. Compared with smooth surface, porous surface allows implant incorporation via bone ingrowth, but is also a subject to bacterial attachment. Non-cytotoxic silver–polysaccharide nanocomposite coatings may provide a way to decrease the risk of bacterial contamination of porous FRC structures. This study is focused on the in vitro characterization of the effect porosity on the antimicrobial efficiency of the coatings against Staphylococcus aureus and Pseudomonas aeruginosa by a series of microbiological tests (initial adhesion, antimicrobial efficacy, and biofilm formation). Characterization included confocal laser scanning microscopy and scanning electron microscopy. The effect of porosity on the initial attachment of S. aureus was pronounced, but in the case of P. aeruginosa the effect was negligible. There were no significant effects of the coatings on the initial bacterial attachment. In the antimicrobial efficacy test, the coatings were potent against both strains regardless of the sample morphology. In the biofilm tests, there were no clear effects either of morphology or of the coating. Further coating development is foreseen to achieve a longer-term antimicrobial effect to inhibiting bacterial implant colonization.  相似文献   
350.
The aim of this paper is to analyse how materials supply systems can be evaluated during product development projects in a concurrent engineering context. The focus is on performance assessment of materials supply systems and the input data required. A case study was conducted in close cooperation with a company and two performance measures were assessed during the concept definition phase and recalculated during the product and process validation phase. The results show that preliminary input data can be used to calculate performance measures by means of the following approaches: indicators, standards or scenarios. Furthermore, it is discussed how performance assessment can assist the materials supply systems design process in a concurrent engineering context by facilitating early problem discovery, early decision-making, and common understanding.  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