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   759篇
  免费   50篇
  国内免费   4篇
电工技术   14篇
综合类   4篇
化学工业   179篇
金属工艺   9篇
机械仪表   12篇
建筑科学   39篇
矿业工程   2篇
能源动力   21篇
轻工业   53篇
水利工程   9篇
石油天然气   8篇
无线电   71篇
一般工业技术   190篇
冶金工业   98篇
原子能技术   7篇
自动化技术   97篇
  2024年   3篇
  2023年   12篇
  2022年   7篇
  2021年   35篇
  2020年   28篇
  2019年   24篇
  2018年   23篇
  2017年   21篇
  2016年   20篇
  2015年   26篇
  2014年   23篇
  2013年   49篇
  2012年   44篇
  2011年   62篇
  2010年   61篇
  2009年   28篇
  2008年   42篇
  2007年   37篇
  2006年   37篇
  2005年   27篇
  2004年   21篇
  2003年   19篇
  2002年   5篇
  2001年   4篇
  2000年   10篇
  1999年   7篇
  1998年   12篇
  1997年   11篇
  1996年   7篇
  1995年   6篇
  1994年   8篇
  1993年   3篇
  1992年   5篇
  1991年   7篇
  1990年   12篇
  1989年   3篇
  1988年   2篇
  1987年   5篇
  1986年   10篇
  1985年   4篇
  1984年   5篇
  1983年   9篇
  1981年   5篇
  1980年   3篇
  1979年   3篇
  1978年   3篇
  1977年   3篇
  1976年   4篇
  1975年   2篇
  1946年   1篇
排序方式: 共有813条查询结果,搜索用时 156 毫秒
21.
Luke  Oren  Alon 《Journal of Web Semantics》2004,2(2):153-183
This paper investigates how the vision of the Semantic Web can be carried over to the realm of email. We introduce a general notion of semantic email, in which an email message consists of a structured query or update coupled with corresponding explanatory text. Semantic email opens the door to a wide range of automated, email-mediated applications with formally guaranteed properties. In particular, this paper introduces a broad class of semantic email processes. For example, consider the process of sending an email to a program committee, asking who will attend the PC dinner, automatically collecting the responses, and tallying them up. We define both logical and decision-theoretic models where an email process is modeled as a set of updates to a data set on which we specify goals via certain constraints or utilities. We then describe a set of inference problems that arise while trying to satisfy these goals and analyze their computational tractability. In particular, we show that for the logical model it is possible to automatically infer which email responses are acceptable w.r.t. a set of constraints in polynomial time, and for the decision-theoretic model it is possible to compute the optimal message-handling policy in polynomial time. In addition, we show how to automatically generate explanations for a process's actions, and identify cases where such explanations can be generated in polynomial time. Finally, we discuss our publicly available implementation of semantic email and outline research challenges in this realm.1  相似文献   
22.
采用阳离子交换的方法对蒙脱土进行了有机改性,使蒙脱土由亲水性变成亲油性,并使其层间距由原来的1.2nm扩大到2.2nm。分别使用甲基四氢苯酐和4,4’-二胺基二苯基甲烷为固化剂,制备两种环氧树脂/蒙脱土纳米复合材料,并用x一射线衍射仪和透射电镜(TEM)分析有机蒙脱土在环氧树脂中的剥离行为。研究表明,固化剂的选择对有机蒙脱土的剥离行为有很大的影响,用固化剂甲基四氢苯酐和促进剂苄基二甲胺后,有机蒙脱土容易被剥离而得到剥离型的纳米复合材料,而用4,4’-二胺基二苯基甲烷固化剂未能使有机蒙脱土剥离后形成插层型纳米复合材料。  相似文献   
23.
Abstract— Defect‐free large‐area inorganic thick‐dielectric EL (TDEL) displays using Color by Blue (CBB) technology have been successfully developed. We have achieved the world's highest blue‐phosphor luminance of 900 cd/m2 for a single‐pixel device by using CBB and by optimizing the e‐beam gun configuration and the flow rate of H2S in the vacuum chamber. By analyzing the defects on panels with triple‐pattern phosphors and CBB panels, we also found that the number of defects on CBB panels can be drastically reduced compared with those on triple‐pattern panels. The defect‐free 17‐in. VGA CBB panels show better characteristics, a high peak luminance of 600 cd/m2 and a high contrast ratio of 1000:1, compared with those of triple‐pattern panels.  相似文献   
24.
Abstract

Like electrical circuit components, the vascular beds in organs present impedance to waves in systemic circulation. In this study, the authors design an animal experiment to study the effect of the impedance to the pressure waves. We view the systemic circulation as an electrical circuit network, and interpret the vascular beds in organs as lumped components in the electrical circuit. Nature's designing of the systemic circulation minimizes the pressure wave reflection, and maximizes blood distribution. This is very similar to the concept adopted by electrical engineers in designing electrical circuits.  相似文献   
25.
Due to the deficiencies of current commercially available biological bone grafts, alternative bone graft substitutes have come to the forefront of tissue engineering in recent times. The main challenge for scientists in manufacturing bone graft substitutes is to obtain a scaffold that has sufficient mechanical strength and bioactive properties to promote formation of new tissue. The ability to synthesise hydrogel based composite scaffolds using photopolymerisation has been demonstrated in this study. The prepared hydrogel based composites were characterised using techniques including Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), Energy-dispersive X-ray spectrometry (EDX), rheological studies and compression testing. In addition, gel fraction, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), porosity and swelling studies of the composites were carried out. It was found that these novel hydrogel bioglass composite formulations did not display the inherent brittleness that is typically associated with bioactive glass based bone graft materials and exhibited enhanced biomechanical properties compared to the polyethylene glycol hydrogel scaffolds along. Together, the combination of enhanced mechanical properties and the deposition of apatite on the surface of these hydrogel based composites make them an ideal candidate as bone graft substitutes in cancellous bone defects or low load bearing applications.  相似文献   
26.
27.
Secondhand electronic cigarette (e-cigarette) aerosol (SHA) might impair indoor air quality and expose bystanders. This study aims to investigate exposure to SHA in controlled conditions of enclosed settings simulating real-world scenario. An experiment was performed in a car and in a room, in which SHA was generated during a 30-minute ad libitum use of an e-cigarette. The experiment was replicated on five consecutive days in each setting. We measured PM2.5, airborne nicotine concentrations, and biomarkers of exposure to SHA, such as nicotine metabolites, tobacco-specific nitrosamines, propylene glycol, and glycerol in bystanders’ saliva samples before, during, and after the exposure period. Self-reported health symptoms related to exposure to SHA were also recorded. The results showed that the highest median PM2.5 concentration was recorded during the exposure period, being 21 µg/m3 in the room setting and 16 µg/m3 in the car setting—about twofold increase compared to the baseline. Most concentrations of the airborne nicotine and all biomarkers were below the limit of quantification in both settings. Bystanders in both settings experienced some short-term irritation symptoms, expressed as dry throat, nose, eyes, and phlegm. In conclusion, short-term use of an e-cigarette in confined spaces increased indoor PM2.5 level and caused some irritation symptoms in bystanders.  相似文献   
28.
In this work, we investigate the thermal boundary resistance and thermal conductivity of GaN layers grown on Si with 100 nm AlN transition layers using time domain thermoreflectance (TDTR). The GaN layers ranged from 0.31 to 1.27 μm. Due to the challenges in determining the thermal boundary resistance of the buried interfaces found in this architecture, a new data reduction scheme for TDTR that utilizes a Monte Carlo fitting method is introduced and found to dramatically reduce the uncertainty in certain model parameters. The results show that the GaN thermal conductivity does not change significantly with layer thickness, whereas the resistance of the AlN layer decreases slightly with GaN thickness.  相似文献   
29.
30.
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