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   12937篇
  免费   319篇
  国内免费   262篇
电工技术   327篇
技术理论   1篇
综合类   519篇
化学工业   2233篇
金属工艺   152篇
机械仪表   323篇
建筑科学   1363篇
矿业工程   373篇
能源动力   3878篇
轻工业   406篇
水利工程   718篇
石油天然气   186篇
武器工业   26篇
无线电   235篇
一般工业技术   421篇
冶金工业   842篇
原子能技术   294篇
自动化技术   1221篇
  2024年   15篇
  2023年   149篇
  2022年   271篇
  2021年   388篇
  2020年   395篇
  2019年   320篇
  2018年   268篇
  2017年   327篇
  2016年   368篇
  2015年   328篇
  2014年   666篇
  2013年   698篇
  2012年   699篇
  2011年   1192篇
  2010年   967篇
  2009年   885篇
  2008年   837篇
  2007年   876篇
  2006年   640篇
  2005年   526篇
  2004年   480篇
  2003年   409篇
  2002年   338篇
  2001年   282篇
  2000年   195篇
  1999年   181篇
  1998年   130篇
  1997年   112篇
  1996年   98篇
  1995年   68篇
  1994年   62篇
  1993年   48篇
  1992年   46篇
  1991年   40篇
  1990年   46篇
  1989年   24篇
  1988年   26篇
  1987年   16篇
  1986年   15篇
  1985年   18篇
  1984年   12篇
  1983年   11篇
  1982年   8篇
  1981年   4篇
  1980年   5篇
  1979年   4篇
  1978年   5篇
  1976年   3篇
  1974年   3篇
  1964年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
The specifics of business intelligence systems compared to operational IS motivate the necessity to research the business intelligence systems acceptance determinants separately. The authors followed an exploratory approach in order to conceptualize a business intelligence acceptance model. Their findings show that in the Business Intelligence Systems context, there is a significant emphasis on organizational factors, such as result demonstrability, social influence, and facilitating conditions with sufficient resources that help build an adequate information culture all substantially influencing the effective acceptance of business intelligence systems.  相似文献   
52.
Abstract

Without prior searching instruction, undergraduate novices wrote structured self-reports during their first session on a Web search engine. Users chose their own topics and followed written instructions that prompted them to describe thoughts and feelings during specified stages of the search: pre-search formulation; search statement formulation; search strategy; and evaluation of results. The sentences in the self-reports were numbered and then coded according to their affective or cognitive function. The affective sentences reveal how users set goals and limit the scope of the cognitive operations. Search acts appear to be governed by an affective filter that organizes incoming information and provides criteria for ranking cognitive relevance to search goal. The cognitive sentences reveal a variety of operations in executing searches. Following the search, students made self-ratings on self-confidence as searchers and satisfaction with the search experience, with explanations of their ratings. Content analysis identified reasons users have for rating self-confidence, stress level, satisfaction, usefulness, and success with future searches.  相似文献   
53.
This paper reports on a case study of a teacher from a technical education institution who explored the educational affordances of PDA technology over a period of six months. Based on this teacher’s perspectives, the study was designed to inform our own understanding of educational affordances of this new and emerging technology. Understanding of educational affordances is important in the context of planning a suitable intervention to support pedagogically effective integration of PDA technology. The study explicated a set of five affordances of PDA technology: as a multimedia-access tool, connectivity tool, capture tool, representational tool and analytical tool. We call on further research to expand this set into a more comprehensive collage of educational affordances of PDA technology.  相似文献   
54.
该文给出了UML的概念与要点,应用UML对教学考评系统进行了建模。给出了系统的用例模型、整体结构模型、静态模型、动态模型,并分析了模型对教学考评变化的可适应性。  相似文献   
55.
面向对象建模技术有利于从全局的角度对系统加以设计。该文在明确面向对象建模技术重要性的基础上,分析了面向对象建模的技术基础,并以社会保险管理系统为案例,探讨了面向对象建模技术的应用,涉及到对象及候选类的确定、用例图及类图的设计等。该文对相关系统的面向对象建模应用提供了一定的借鉴作用。  相似文献   
56.
线面拓扑和度量关系的细分描述和计算方法   总被引:1,自引:0,他引:1  
由于单独的拓扑关系、度量关系无法区分复杂要素之间的空间关系,在语义描述上存在歧义,提出一种二维空间R~2下空间关系的细分表达模型.该模型将面与线求交后,线面可以表示成n-1个拓扑和度量分量的序列矩阵,在语义上进行更细致的分段描述;采用折线节点微小圆求交的算法,考虑面带洞和目标的不确定性,归纳出线面拓扑关系细分判断的7个规则,以及长度、分割度等度量项的计算方法.最后以土地利用中图斑扣除线状地物计算地类面积为实例,验证了该模型和计算方法对解决实际问题的有效性.  相似文献   
57.
艺术的创造性为人类留下的无数艺术珍品,使人能领略到人性的充实和伟大的智慧,也领略到了人类文明的伟大,增强了人类的尊严与荣耀。每件艺术品都反映和保存各个相关时期的地区、政治、文化、宗教、习俗等内容。受到这些因素的影响,使得艺术形式多种多样丰富多彩。我认为,最有魅力的是在宗教意识下的艺术形式。  相似文献   
58.
通过结合网站设计初期的网站结构和典型用例的预先定义,构建一个基于Web日志数据的用户访问数据分析系统。该系统(AS-UAB,Analysis System of User Access Behaviors)通过对网站结构和典型用例的预先植入,利用该领域最新的研究方法和结论,为网站相关人员提供可视化的用户访问信息统计及趋势预测,网站结构设计及交互设计上存在的问题及改进建议等通用功能和个性化定制功能。  相似文献   
59.
Observed finger behaviour during computer mouse use   总被引:1,自引:0,他引:1  
Two-button computer mouse users may exhibit sustained, static finger lifting behaviours to prevent inadvertent activations by avoiding finger pressure on the buttons, which leads to prolonged, static finger extensor muscle loading. One hundred graduate students were observed during normal computer work in a university computer facility to qualify and quantify the prevalence of lifted finger behaviours and extended finger postures, as well as wrist/forearm and grip behaviour, during specific mouse activities. The highest prevalences observed were 48% of the students lifted their middle finger during mouse drag activities, and 23% extended their middle finger while moving the mouse. In addition, 98% of the students rested their wrist and forearm (77%) or wrist only (21%) on the workstation surface, and 97% had an extended wrist posture (15 degrees -30 degrees ) when using the mouse. Potential applications of these findings include future computer input device designs to reduce finger lifting behaviour and exposures to risk factors of hand/forearm musculoskeletal pain.  相似文献   
60.
Land use and land cover (LULC) maps from remote sensing are vital for monitoring, understanding and predicting the effects of complex human-nature interactions that span local, regional and global scales. We present a method to map annual LULC at a regional spatial scale with source data and processing techniques that permit scaling to broader spatial and temporal scales, while maintaining a consistent classification scheme and accuracy. Using the Dry Chaco ecoregion in Argentina, Bolivia and Paraguay as a test site, we derived a suite of predictor variables from 2001 to 2007 from the MODIS 250 m vegetation index product (MOD13Q1). These variables included: annual statistics of red, near infrared, and enhanced vegetation index (EVI), phenological metrics derived from EVI time series data, and slope and elevation. For reference data, we visually interpreted percent cover of eight classes at locations with high-resolution QuickBird imagery in Google Earth. An adjustable majority cover threshold was used to assign samples to a dominant class. When compared to field data, we found this imagery to have georeferencing error < 5% the length of a MODIS pixel, while most class interpretation error was related to confusion between agriculture and herbaceous vegetation. We used the Random Forests classifier to identify the best sets of predictor variables and percent cover thresholds for discriminating our LULC classes. The best variable set included all predictor variables and a cover threshold of 80%. This optimal Random Forests was used to map LULC for each year between 2001 and 2007, followed by a per-pixel, 3-year temporal filter to remove disallowed LULC transitions. Our sequence of maps had an overall accuracy of 79.3%, producer accuracy from 51.4% (plantation) to 95.8% (woody vegetation), and user accuracy from 58.9% (herbaceous vegetation) to 100.0% (water). We attributed map class confusion to limited spectral information, sub-pixel spectral mixing, georeferencing error and human error in interpreting reference samples. We used our maps to assess woody vegetation change in the Dry Chaco from 2002 to 2006, which was characterized by rapid deforestation related to soybean and planted pasture expansion. This method can be easily applied to other regions or continents to produce spatially and temporally consistent information on annual LULC.  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