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   685篇
  免费   43篇
  国内免费   1篇
电工技术   6篇
综合类   3篇
化学工业   179篇
金属工艺   20篇
机械仪表   10篇
建筑科学   46篇
能源动力   23篇
轻工业   58篇
水利工程   5篇
石油天然气   1篇
无线电   35篇
一般工业技术   142篇
冶金工业   57篇
原子能技术   5篇
自动化技术   139篇
  2024年   2篇
  2023年   15篇
  2022年   17篇
  2021年   27篇
  2020年   19篇
  2019年   20篇
  2018年   26篇
  2017年   17篇
  2016年   35篇
  2015年   24篇
  2014年   32篇
  2013年   47篇
  2012年   48篇
  2011年   49篇
  2010年   38篇
  2009年   33篇
  2008年   27篇
  2007年   25篇
  2006年   27篇
  2005年   16篇
  2004年   15篇
  2003年   9篇
  2002年   17篇
  2001年   9篇
  2000年   8篇
  1999年   9篇
  1998年   10篇
  1997年   3篇
  1996年   6篇
  1995年   5篇
  1994年   12篇
  1993年   8篇
  1992年   3篇
  1991年   7篇
  1990年   5篇
  1989年   4篇
  1988年   4篇
  1987年   3篇
  1985年   3篇
  1984年   2篇
  1983年   4篇
  1982年   7篇
  1981年   2篇
  1980年   6篇
  1979年   4篇
  1978年   3篇
  1975年   5篇
  1973年   3篇
  1969年   2篇
  1931年   1篇
排序方式: 共有729条查询结果,搜索用时 109 毫秒
691.
A theory for focused optical beams at planar structures is described. It is an extension of a previous theory based on summation of plane waves. The focused beam is obtained by an imaginary shift in the position vector of the plane waves. It is well suited for calculations of electromagnetic fields at planar surface plasmon resonance structures excited by a focused optical beam.  相似文献   
692.
Increasingly, drug-discovery processes focus on complete gene families. Tools for analyzing similarities and differences across protein families are important for the understanding of key functional features of proteins. Herein we present a method for classifying protein families on the basis of the properties of their active sites. We have developed Cavbase, a method for describing and comparing protein binding pockets, and show its application to the functional classification of the binding pockets of the protein family of protein kinases. A diverse set of kinase cavities is mutually compared and analyzed in terms of recurring functional recognition patterns in the active sites. We are able to propose a relevant classification based on the binding motifs in the active sites. The obtained classification provides a novel perspective on functional properties across protein space. The classification of the MAP and the c-Abl kinases is analyzed in detail, showing a clear separation of the respective kinase subfamilies. Remarkable cross-relations among protein kinases are detected, in contrast to sequence-based classifications, which are not able to detect these relations. Furthermore, our classification is able to highlight features important in the optimization of protein kinase inhibitors. Using small-molecule inhibition data we could rationalize cross-reactivities between unrelated kinases which become apparent in the structural comparison of their binding sites. This procedure helps in the identification of other possible kinase targets that behave similarly in "binding pocket space" to the kinase under consideration.  相似文献   
693.
A three-dimensional numerical model was applied to compute uniform and nonuniform sediment transport and bed deformation in an S-shaped laboratory channel located at the University of Innsbruck, where detailed measurements of the velocity field and bed elevation changes were made. The channel had two bends, a trapezoidal cross section, and a slope of S = 0.005. Gravel with a mean diameter of 4.2?mm was used as movable bed material and for sediment feeding. Wu’s formula for multiple grain sizes was compared with van Rijn’s formula using one grain size. Fairly good agreement was found between the computed and measured bed elevations for both approaches, whereas Wu’s formula could further improve the numerical results. Looking at the physics of the erosion pattern, the computed scour areas were located slightly more downstream than what was observed in the physical model. The current study also includes several parameter tests: grid distribution in vertical, lateral, and longitudinal direction; time step; number of inner iterations/time step; active sediment layer thickness; and the Shields coefficient. The variation of those parameters gave some differences in the results, but the overall pattern of bed elevation changes remained the same.  相似文献   
694.
This paper describes the standardisation process and introduction timeline of high definition television. The development of the standard is a process that goes back over 40 years, but HDTV is only today slowly finding its place in the home entertainment market. This paper explores why the European standard for analogue HDTV was not widely adopted, what Europe’s relation to HDTV means today, and proposes some general lessons that can be learned for the benefit of the development of HDTV’s successor, Ultra HDTV aka Super Hi-Vision.  相似文献   
695.
The paper proposes a location-aware mobile Intrusion Prevention System (mIPS) architecture with enhanced privacy that is integrated in Managed Security Service (MSS). The solution is envisaged in a future fifth generation telecommunications (5G) context with increased but varying bandwidth, a virtualised execution environment and infrastructure that allows threads, processes, virtual machines and storage to be migrated to cloud computing services on demand, to dynamically scale performance and save power. 5G mobile devices will be attractive targets for malicious software, and this threat will in some cases change with location. Mobile devices will store more sensitive information and will also be used to a larger extent for sensitive transactions than they typically do today. In addition, a distributed execution environment in itself gives raise to some new security challenges. In order to handle these security challenges, we have proposed the location-aware mIPS architecture, which benefits from a distributed execution environment where processor intensive services can be outsourced to Cloud hosting providers. The mIPS supports querying location threat profiles in a privacy-preserving way, and ensures that mIPS alerts sent to the the first-line MSS are anonymised. We finally perform an analysis of potential strengths and weaknesses of the proposed approach.  相似文献   
696.
The influence of carbon content and porosity of lithium vanadium phosphate, Li3V2(PO4)3, on its diffusion properties and electrochemical performance was examined by GITT and galvanostatic charge/discharge experiments. The diffusion coefficient of Li3V2(PO4)3, as determined by GITT measurements, appears relatively high, thus making this material interesting also for high power application. Moreover, the results of this study clearly show that the porosity and the carbon content of the electrode materials is an important factor affecting the diffusion as well as the electrochemical performance of Li3V2(PO4)3. It was demonstrated that excessive carbon coating may lead to kinetic hindrances but may also contribute specific capacity in anode materials in voltage regions below 1.0 V versus Li/Li+.  相似文献   
697.
Thoracic aortic aneurysm and dissection (TAAD) is a major cause of cardiovascular morbidity and mortality. Loss-of-function variants in LOX, encoding the extracellular matrix crosslinking enzyme lysyl oxidase, have been reported to cause familial TAAD. Using a next-generation TAAD gene panel, we identified five additional probands carrying LOX variants, including two missense variants affecting highly conserved amino acids in the LOX catalytic domain and three truncating variants. Connective tissue manifestations are apparent in a substantial fraction of the variant carriers. Some LOX variant carriers presented with TAAD early in life, while others had normal aortic diameters at an advanced age. Finally, we identified the first patient with spontaneous coronary artery dissection carrying a LOX variant. In conclusion, our data demonstrate that loss-of-function LOX variants cause a spectrum of aortic and arterial aneurysmal disease, often combined with connective tissue findings.  相似文献   
698.
Textile fibers and yarns of high conductivity, and their integration into wearable textiles for different electronic applications, have become an important research field for many research groups throughout the world. We have produced novel electrically conductive textile yarns by vapor‐phase polymerization (VPP) of a conjugated polymer, poly(3,4‐ethylenedioxythiophene) (PEDOT), on the surface of commercially available textile yarns (viscose). In this article, we have presented a novel setup for electrical resistance measurements, which can be used not only for fibrous structures but also for woven structures of specific dimensions. We have reported a two‐point resistance‐measuring method using an already manufactured setup and also a comparison with the conventionally used method (so‐called crocodile clip method). We found that the electrical properties of PEDOT‐coated viscose fibers strongly depend on the concentration of oxidant (FeCl3) and the doping (oxidation) process of PEDOT. To evaluate the results, we used mass specific resistance values of PEDOT‐coated viscose yarns instead of normal surface resistance values. The voltage–current (VI) characteristics support the ohmic behavior of coated fibers to some extent. Monitoring of the charging effect of the flow of current through conductive fibers for prolonged periods of time showed that conductivity remains constant. The change in electrical resistance values with increase in the length of coated fibers was also reported. The resistance‐measuring setup employed could also be used for continuous measurement of resistance in the production of conductive fibers, as well as for four‐point resistance measurement. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012  相似文献   
699.
The toxic effects of cadmium, cobalt, uranium and zinc to the bacterium Zoogloea ramigera have been studied. This organism, which is abundant in sewage-treatment plants, responded to media supplemented with heavy metals by showing a prolonged lag phase and by decreasing its growth rate. The length of the lag phase was proportional to the metal concentration when Z. ramigera was exposed to cadmium, cobalt and zinc. When exposed to uranium (uranyl ions) the organism altered its growth behavior by showing an extended lag phase almost independent of the metal concentration. The order of toxicity of the metals to Z. ramigera was Cd2+ = Zn2+ > Co2+ > UO22+.  相似文献   
700.
Oxygen uptake by soft bottom sediments was measured in situ with an oxygen electrode in a bell jar. Values in the range 0·3-3·0 g O2 m−2 d−1 were obtained at 19 localities in fresh and brackish water. Comparative measurements were made in the laboratory on sediment cores. These gave consistently lower values than the in situ measurements. Laboratory experiments showed that the oxygen uptake depended on the oxygen concentration and that the temperature coefficient decreased with increasing temperature. There was no simple correlation between oxygen uptake and content organic matter in sediments.  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