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   7996篇
  免费   477篇
  国内免费   13篇
电工技术   77篇
综合类   11篇
化学工业   3083篇
金属工艺   117篇
机械仪表   135篇
建筑科学   301篇
矿业工程   43篇
能源动力   195篇
轻工业   1295篇
水利工程   46篇
石油天然气   38篇
无线电   331篇
一般工业技术   1216篇
冶金工业   744篇
原子能技术   21篇
自动化技术   833篇
  2024年   19篇
  2023年   129篇
  2022年   677篇
  2021年   804篇
  2020年   246篇
  2019年   241篇
  2018年   305篇
  2017年   250篇
  2016年   320篇
  2015年   271篇
  2014年   327篇
  2013年   534篇
  2012年   446篇
  2011年   491篇
  2010年   327篇
  2009年   325篇
  2008年   320篇
  2007年   290篇
  2006年   247篇
  2005年   189篇
  2004年   158篇
  2003年   136篇
  2002年   128篇
  2001年   68篇
  2000年   62篇
  1999年   75篇
  1998年   158篇
  1997年   117篇
  1996年   105篇
  1995年   65篇
  1994年   59篇
  1993年   54篇
  1992年   37篇
  1991年   23篇
  1990年   35篇
  1989年   17篇
  1988年   31篇
  1987年   22篇
  1986年   16篇
  1985年   35篇
  1984年   30篇
  1983年   30篇
  1982年   14篇
  1981年   27篇
  1980年   24篇
  1979年   17篇
  1977年   20篇
  1976年   35篇
  1973年   12篇
  1940年   10篇
排序方式: 共有8486条查询结果,搜索用时 15 毫秒
71.
We combine Auto Identification and Web technologies in an extensible on-site event support system for enhancing experience of conference organizers as well as participants. Our system enables users to authenticate themselves using RFID badges and to access interactive, Web-based services via a touchscreen PC. The developed services aim at supporting social interactions of participants, and thus validate the promising usage directions of the combination of offline social networks and the online social Web. The main hypothesis of our work is that: ??A sensor based information system can truly enhance social conference experience.?? Technically, we have investigated employment of Web 2.0 technologies in social, sensor and mobile technologies enabled systems at conferences and events. This article gives an overview of the overall system and its evaluation via a user survey and usage log data collected during the Extended Semantic Web Conference (ESWC) 2010 and similar international conferences, altogether with several hundred participants.  相似文献   
72.
73.
Avian biodiversity is threatened, and in order to prioritize limited conservation resources and conduct effective conservation planning a better understanding of avian species richness patterns is needed. The use of image texture measures, as a proxy for the spatial structure of land cover and vegetation, has proven useful in explaining patterns of avian abundance and species richness. However, prior studies that modeled habitat with texture measures were conducted over small geographical extents and typically focused on a single habitat type. Our goal was to evaluate the performance of texture measures over broad spatial extents and across multiple habitat types with varying levels of vertical habitat structure. We calculated a suite of texture measures from 114 Landsat images over a study area of 1,498,000 km2 in the Midwestern United States, which included habitats ranging from grassland to forest. Avian species richness was modeled for several functional guilds as a function of image texture. We subsequently compared the explanatory power of texture-only models with models fitted using landscape composition metrics derived from the National Land Cover Dataset, as well as models fitted using both texture and composition metrics. Measures of image texture were effective in modeling spatial patterns of avian species richness in multiple habitat types, explaining up to 51% of the variability in species richness of permanent resident birds. In comparison, landscape composition metrics explained up to 56% of the variability in permanent resident species richness. In the most heavily forested ecoregion, texture-measures outperformed landscape metrics, and the two types of measurements were complementary in multivariate models. However, in two out of three ecoregions examined, landscape composition metrics consistently performed slightly better than texture measures, and the variance explained by the two types of measures overlapped considerably. These results show that image texture measures derived from satellite imagery can be an important tool for modeling patterns of avian species richness at broad spatial extents, and thus assist in conservation planning. However, texture measures were slightly inferior to landscape composition metrics in about three-fourths of our models. Therefore texture measures are best considered in conjunction with landscape metrics (if available) and are best used when they show explanatory ability that is complementarity to landscape metrics.  相似文献   
74.
75.
高性能电力应用致力于搭建用于调度数据的统一管理、集中处理平台。数据网格易于海量数据共享的特点使其适用于实现调度主站一体化。构建了调度主站数据网格的基本架构,利用网格软件Globus Toolkit建立网格环境,在此基础上配置数据库访问中间件OGSA-DAI来建立面向调度主站一体化的数据网格实验平台。  相似文献   
76.
The symmetry of the Bloch functions in the conduction band of tetragonal and orthorhombic La2CuO4 is examined for the existence of symmetry-adapted and optimally localizable (usual or spin-dependent) Wannier functions. It turns out that such Wannier functions do not exist in the tetragonal phase. In the orthorhombic phase, on the other hand, the Bloch functions can be unitarily transformed in three different ways into optimally localizable Wannier functions: they can be chosen to be adapted to each of the three phases observed in the pure or doped material, that is, to the antiferromagnetic phase, to the superconducting phase or to the phase evincing neither magnetism nor superconductivity. This group-theoretical result is proposed to be interpreted within a nonadiabatic extension of the Heisenberg model. Within this model, atomic-like states represented by these Wannier functions are responsible for the stability of each of the three phases. However, all the three atomic-like states cannot exist in the tetragonal phase, but are stabilized by the orthorhombic distortion of the crystal. A simple model is proposed which may explain the physical properties of La2−x Sr x CuO4 as a function of the Sr concentrationx.  相似文献   
77.
The experiments are aimed at the study of the interfacial dilational properties, under microgravity conditions. The examined systems are aqueous solutions of the surfactant n-dodecyl-dimethylphosphine oxide, at different concentrations and temperatures. Low frequency harmonic disturbances are imposed to the interfacial area of an air bubble. Also square pulse disturbances are imposed to each studied system. The experimental results grant information about the dynamics of air-liquid single interfaces.  相似文献   
78.
The present work shows the first experimental and theoretical results for investigations on the rheology of liquid films. The experiments are planned to be performed under microgravity conditions. This environment will allow forming films of different thickness, which is impossible under ground conditions due to drainage. Then the films are forced to harmonic oscillations of the film area so that the film elasticity can be measured as a function of frequency. The presented theoretical model demonstrates the main relationships to be solved under corresponding boundary conditions  相似文献   
79.
This paper presents ALIAS, an agent architecture based on intelligent logic agents, where the main form of agent reasoning is abduction. The system is particularly suited for solving problems where knowledge is incomplete, where agents may need to make reasonable hypotheses about the problem domain and other agents, and where the raised hypotheses have to be consistent for the overall set of agents. ALIAS agents are pro-active, exhibiting a goal-directed behavior, and autonomous, since each one can solve problems using its own private knowledge base. ALIAS agents are also social, because they are able to interact with other agents, in order to cooperatively solve problems. The coordination mechanisms are modeled by means of LAILA, a logic-based language which allows to express intra-agent reasoning and inter-agent coordination. As an application, we show how LAILA can be used to implement inter-agent dialogues, e.g., for negotiation. In particular, LAILA is well-suited to coordinate the process of negotiation aimed at exchanging resources between agents, thus allowing them to execute the plans to achieve their goals.  相似文献   
80.
A database model for object dynamics   总被引:1,自引:0,他引:1  
To effectively model complex applications in which constantly changing situations can be represented, a database system must be able to support the runtime specification of structural and behavioral nuances for objects on an individual or group basis. This paper introduces the role mechanism as an extension of object-oriented databases to support unanticipated behavioral oscillations for objects that may attain many types and share a single object identity. A role refers to the ability to represent object dynamics by seamlessly integrating idiosyncratic behavior, possibly in response to external events, with pre-existing object behavior specified at instance creation time. In this manner, the same object can simultaneously be an instance of different classes which symbolize the different roles that this object assumes. The role concept and its underlying linguistic scheme simplify the design requirements of complex applications that need to create and manipulate dynamic objects. Edited by D. McLeod / Received March 1994 / Accepted January 1996  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