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   17368篇
  免费   3016篇
  国内免费   1685篇
电工技术   2463篇
技术理论   2篇
综合类   2006篇
化学工业   376篇
金属工艺   258篇
机械仪表   934篇
建筑科学   3415篇
矿业工程   547篇
能源动力   298篇
轻工业   236篇
水利工程   802篇
石油天然气   288篇
武器工业   189篇
无线电   2974篇
一般工业技术   1076篇
冶金工业   827篇
原子能技术   159篇
自动化技术   5219篇
  2024年   87篇
  2023年   309篇
  2022年   647篇
  2021年   664篇
  2020年   818篇
  2019年   668篇
  2018年   606篇
  2017年   767篇
  2016年   763篇
  2015年   943篇
  2014年   1236篇
  2013年   1244篇
  2012年   1457篇
  2011年   1513篇
  2010年   1244篇
  2009年   1134篇
  2008年   1252篇
  2007年   1355篇
  2006年   1035篇
  2005年   866篇
  2004年   756篇
  2003年   598篇
  2002年   411篇
  2001年   355篇
  2000年   274篇
  1999年   233篇
  1998年   166篇
  1997年   132篇
  1996年   104篇
  1995年   72篇
  1994年   71篇
  1993年   38篇
  1992年   46篇
  1991年   38篇
  1990年   32篇
  1989年   21篇
  1988年   15篇
  1987年   14篇
  1986年   8篇
  1985年   14篇
  1984年   14篇
  1983年   11篇
  1982年   3篇
  1981年   3篇
  1979年   3篇
  1966年   4篇
  1965年   3篇
  1959年   5篇
  1957年   2篇
  1956年   2篇
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
21.
朱朝晖  李涛 《信息技术》2006,30(8):89-91
测向定位技术是无线电管理的一个重要课题。测向定位过程中的误差的种类和产生的原因很多。选择适当的方法对误差进行校正,可以有效的减小测向误差带来的损失,提高无线电管理的效率。  相似文献   
22.
作者应用地质统计学原理与方法,在山东簸箕李引黄灌区开展大尺度区域水土特性参数时空变异性的研究,描述农田排水、地下水、表层土壤中含盐量的空间与时间变化分布趋势和特征,分析其间存在的相关关系。结果表明,在一个完整的水文循环年内,研究区域的水土特性参数之间具有相近的空间变异分布状态和特点,但却表现出不同的时间变异分布趋势与特征。农田排水和表层土壤的含盐量随季节变化的分布状态在灌区上、下游相对稳定,在中游却变化明显;地下水的盐分浓度在整个灌区的分布状况没有呈现出明显的时间变异性。在春季至初夏时段内,农田排水中含盐量的增加似乎对地下水水质的影响较小,而对表层土壤积盐状况影响较大。研究成果为灌区制定合理的水资源利用与农田水土管理策略提供了理论依据。  相似文献   
23.
Thirty patients who had undergone either a right or left unilateral temporal lobectomy (14 RTL; 16 LTL) and 16 control participants were tested on a computerized human analogue of the Morris Water Maze. The procedure was designed to compare allocentric and egocentric spatial memory. In the allocentric condition, participants searched for a target location on the screen, guided by object cues. Between trials, participants had to walk around the screen, which disrupted egocentric memory representation. In the egocentric condition, participants remained in the same position, but the object cues were shifted between searches to prevent them from using allocentric memory. Only the RTL group was impaired on the allocentric condition, and neither the LTL nor RTL group was impaired on additional tests of spatial working memory or spatial manipulation. The results support the notion that the right anterior temporal lobe stores long-term allocentric spatial memories. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
24.
文脉中的环节建筑   总被引:2,自引:0,他引:2  
韩冬青 《新建筑》1998,(1):20-22
环节建筑产生于建筑与城市的内在联系之中,它将“文脉”的含义拓展到基地、城市公共空间体系和城市职能等领域。阐述了环节建筑的基本概念,在此基础上分析了环节建筑在上述三个领域中所扮演的角色及其相互关系。  相似文献   
25.
Qualitative representation of spatial knowledge in two-dimensional space   总被引:3,自引:0,他引:3  
Various relation-based systems, concerned with the qualitative representation and processing of spatial knowledge, have been developed in numerous application domains. In this article, we identify the common concepts underlying qualitative spatial knowledge representation, we compare the representational properties of the different systems, and we outline the computational tasks involved in relation-based spatial information processing. We also describesymbolic spatial indexes, relation-based structures that combine several ideas in spatial knowledge representation. A symbolic spatial index is an array that preserves only a set of spatial relations among distinct objects in an image, called the modeling space; the index array discards information, such as shape and size of objects, and irrelevant spatial relations. The construction of a symbolic spatial index from an input image can be thought of as a transformation that keeps only a set of representative points needed to define the relations of the modeling space. By keeping the relative arrangements of the representative points in symbolic spatial indexes and discarding all other points, we maintain enough information to answer queries regarding the spatial relations of the modeling space without the need to access the initial image or an object database. Symbolic spatial indexes can be used to solve problems involving route planning, composition of spatial relations, and update operations.  相似文献   
26.
Management of multidimensional discrete data   总被引:1,自引:0,他引:1  
Spatial database management involves two main categories of data: vector and raster data. The former has received a lot of in-depth investigation; the latter still lacks a sound framework. Current DBMSs either regard raster data as pure byte sequences where the DBMS has no knowledge about the underlying semantics, or they do not complement array structures with storage mechanisms suitable for huge arrays, or they are designed as specialized systems with sophisticated imaging functionality, but no general database capabilities (e.g., a query language). Many types of array data will require database support in the future, notably 2-D images, audio data and general signal-time series (1-D), animations (3-D), static or time-variant voxel fields (3-D and 4-D), and the ISO/IEC PIKS (Programmer's Imaging Kernel System) BasicImage type (5-D). In this article, we propose a comprehensive support ofmultidimensional discrete data (MDD) in databases, including operations on arrays of arbitrary size over arbitrary data types. A set of requirements is developed, a small set of language constructs is proposed (based on a formal algebraic semantics), and a novel MDD architecture is outlined to provide the basis for efficient MDD query evaluation.  相似文献   
27.
We introduce a semantic data model to capture the hierarchical, spatial, temporal, and evolutionary semantics of images in pictorial databases. This model mimics the user's conceptual view of the image content, providing the framework and guidelines for preprocessing to extract image features. Based on the model constructs, a spatial evolutionary query language (SEQL), which provides direct image object manipulation capabilities, is presented. With semantic information captured in the model, spatial evolutionary queries are answered efficiently. Using an object-oriented platform, a prototype medical-image management system was implemented at UCLA to demonstrate the feasibility of the proposed approach.  相似文献   
28.
EEPROM的参数设置控制着系统的基本功能,设置的改变对系统的起动和运行起着重要作用。本文详细地列出了EEPROM的地址分配表,并通过上机实验对那些重要的地址了详细的说明。  相似文献   
29.
A small instrument is described which is operated on the stage of a light microscope to trim resin-embedded specimens to precise levels for subsequent ultramicrotomy and to cut thin pilot sections for light microscopy. The operating procedure and examples of results are given.  相似文献   
30.
本主要介绍基于CDMA智能网平台的一种增值业务——“位置服务”,阐述这个业务的网络结构、涉及到的技术问题和解决方案,并将这个整体思路投入到开发业务中去。  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