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   565篇
  免费   13篇
电工技术   10篇
化学工业   65篇
金属工艺   8篇
机械仪表   7篇
建筑科学   13篇
矿业工程   6篇
能源动力   27篇
轻工业   55篇
水利工程   3篇
石油天然气   2篇
无线电   51篇
一般工业技术   69篇
冶金工业   195篇
原子能技术   2篇
自动化技术   65篇
  2021年   4篇
  2020年   7篇
  2019年   6篇
  2018年   4篇
  2017年   6篇
  2016年   3篇
  2015年   7篇
  2014年   9篇
  2013年   25篇
  2012年   14篇
  2011年   28篇
  2010年   17篇
  2009年   23篇
  2008年   20篇
  2007年   18篇
  2006年   24篇
  2005年   22篇
  2004年   11篇
  2003年   10篇
  2002年   17篇
  2001年   6篇
  2000年   16篇
  1999年   14篇
  1998年   48篇
  1997年   22篇
  1996年   33篇
  1995年   17篇
  1994年   16篇
  1993年   10篇
  1992年   5篇
  1991年   4篇
  1990年   11篇
  1989年   9篇
  1988年   4篇
  1987年   4篇
  1986年   5篇
  1985年   5篇
  1984年   4篇
  1983年   2篇
  1982年   3篇
  1981年   8篇
  1980年   6篇
  1978年   3篇
  1977年   5篇
  1976年   14篇
  1974年   5篇
  1972年   5篇
  1971年   2篇
  1969年   5篇
  1967年   2篇
排序方式: 共有578条查询结果,搜索用时 15 毫秒
1.
Recent developments of stability control in mines, essentially based on Ge-doped fiber Bragg gratings (FBG) are reported including results about the different aspects of the system: accurate characterizations of FBG, sensor network topology and multiplexing method, user interface design and sensor packaging  相似文献   
2.
The aim of this paper is to analyze the feasibility of ultrathin packages through the electrical qualification of the technological process used, i.e. mechanical lapping. It considers polysilicon bipolar transistors which thickness can reach values lower than 10 μm. Forward mode and reverse mode characterizations show no significant degradation of pertinent characteristics, thus allowing to find applications in new compact packaging concept.  相似文献   
3.
Being perceptive is a trait highly valued in scientific and engineering professions. What a scientist or engineer notices while considering a problem, evaluating alternatives, or interpreting data has a profound impact on how a problem is viewed and solved. This paper focuses on processes we believe underlie being perceptive: firstly, preparation—becoming attuned to salient or important features; secondly, assimilation-detection and exploration of patterns (invariants) as well as anomalies; and thirdly, strategic control-heuristic strategies for exploring the implications of what has been observed. These processes play an integral role in characteristic activities within creative design, including problem reformulation, the emergence of properties and constraints on the solution, and the ability to incorporate into the design experimental feedback from the environment and from experiences with prototypes and previous designs. The paper presents a computational model incorporating these ideas, implemented in a system called IMPROVISER.  相似文献   
4.
While mitochondrial sequences can be used to probe the time and place of the mitochondrial 'Eve,' nuclear genes can be used to ask a slightly different question: when did humans (members of the genus Homo) or their hominid precursors (the hominids) first leave Africa and fan out over Asia and Europe? If they did so recently, it seems likely that there was a recent African origin of our species, Homo sapiens, rather than multiple origins in various parts of the Old World. A recent paper uses minisatellite data to make the argument that the departure from Africa happened very recently indeed. An alternative explanation for the data is that there was no single and irreversible departure from Africa, but that some peoples migrated back and forth between Africa and the rest of the Old World over the last few tens of thousands of years. For this and other reasons, putting a single date on the farewell to Africa remains problematical.  相似文献   
5.
A multilayer background modeling technique is presented for video surveillance. Rather than simply classifying all features in a scene as either dynamically moving foreground or long-lasting, stationary background, a temporal model is used to place each scene object in time relative to each other. Foreground objects that become stationary are registered as layers on top of the background layer. In this process of layer formation, the algorithm deals with ”fake objects” created by moved background, and noise created by dynamic background and moving foreground objects. Objects that leave the scene are removed based on the occlusion reasoning among layers. The technique allows us to understand and visualize a scene with multiple objects entering, leaving, and occluding each other at different points in time. This scene understanding leads to a richer representation of temporal scene events than traditional foreground/background segmentation. The technique builds on a low-cost background modeling technique that makes it suitable for embedded, real-time platforms.  相似文献   
6.
A series of statistical copolymers derived from 2‐(dimethylamino)ethyl methacrylate with four different hydrophobic comonomers (ethyl, butyl, cyclohexyl, and octyl methacrylates) have been prepared via conventional free radical copolymerization under bulk conditions. The copolymers have been subsequently modified, with 1,3‐propanesultone to yield the corresponding polysulfoproylbetaine derivatives. Those copolymers exhibiting the requisite aqueous solubility have been screened with respect to their antimicrobial activity against two common and notorious pathogens, namely Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). We show that certain copolymers do indeed exhibit antimicrobial activity. The extent of activity is related to the molecular characteristics of the materials such as the molar composition and structure of the hydrophobic comonomer. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1036–1041, 2006  相似文献   
7.
Epoxidized 10-undecenoic acid triglyceride, an experimental seed oil derivative that has a terminal epoxy group on each of the three acyl glyceride segments, has been found to have good reactivity with amine curatives and allows room temperature cures to be obtained. Coatings based on epoxidized 10-undercenoic acid triglyceride have also shown excellent UV stability. As an example, coatings samples placed in a QUVA chamber exhibit no loss in gloss after 3000 hr of a cycled exposure to high intensity UV lamps and moisture at temperatures of 50–60°C. In comparison, coatings based on standard liquid epoxy resins (LERs) and commercially available hydrogenated LERs lose gloss due to chalking/decomposition within 200–800 hr. Presented at the 81 st Annual Meeting of the Federation of Societies for Coatings Technology, November 12–14, 2003, in Philadelphia, PA.  相似文献   
8.
Coherent addition of adjacent lasers by forked eigenstate operation   总被引:1,自引:0,他引:1  
Forked laser eigenstates are shown to provide a powerful tool both to phase lock spatially separated laser oscillators and to add their powers coherently into a TEM(00) output beam. Coherent addition of the powers extracted from two fiber-coupled diode-pumped Nd:YAG channels is theoretically and experimentally demonstrated. Pure TEM(00) oscillation is obtained with a 20% optical-to-optical conversion efficiency. The coherence of the two-propagation-axis laser is proved, and single-frequency operation is demonstrated. The scalability of the scheme is discussed.  相似文献   
9.
Real-time underwater visualization has been extremely slow to develop within the offshore industry and has generally been limited to 2D representations of vessel positions on digital charts. Only recently have marine industries realized the potential of 3D real-time virtual environments and visualization systems for effective management planning and real-time situation awareness. We describe a real-time visualization of the clean-up of a former US Naval Submarine Base, located in Holy Loch, Scotland. Our Whole-Field Modeling System has provided an accurate real-time visualization of numerous varying parameters such as remotely operated vehicles (ROVs), cranes, barges, grabs, magnets, and detailed seabed topography. The system improved the field staffs' spatial and temporal awareness and facilitated decision making within the complex offshore working environment. A side bar discusses another application, offshore diamond mining  相似文献   
10.
The prognosis of epidural haematomas (EDH) is generally favourable if an operation is carried out in good time. Suspected EDH is mostly diagnosed as a result of a "typical" neurological manifestation (initial unconsciousness/asymptomatic interval/loss of consciousness), which then leads to an in-depth diagnosis (X-ray of the skull, CT, MRI). However, atypical clinical manifestations are frequent and can result in dangerous delays in diagnosis and treatment. A decisive factor in the early detection of EDH is close clinical-neurological monitoring by specially trained staff and their prompt reaction when changes occur, no matter how minor. Qualitative changes in the patient's state of consciousness and behaviour are just as important in this respect as quantitative ones.  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