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   3657篇
  免费   188篇
  国内免费   108篇
电工技术   62篇
技术理论   1篇
综合类   170篇
化学工业   409篇
金属工艺   110篇
机械仪表   53篇
建筑科学   293篇
矿业工程   34篇
能源动力   66篇
轻工业   518篇
水利工程   149篇
石油天然气   48篇
武器工业   2篇
无线电   138篇
一般工业技术   236篇
冶金工业   1302篇
原子能技术   14篇
自动化技术   348篇
  2024年   7篇
  2023年   46篇
  2022年   94篇
  2021年   160篇
  2020年   82篇
  2019年   88篇
  2018年   74篇
  2017年   84篇
  2016年   106篇
  2015年   98篇
  2014年   126篇
  2013年   142篇
  2012年   159篇
  2011年   324篇
  2010年   257篇
  2009年   203篇
  2008年   222篇
  2007年   273篇
  2006年   212篇
  2005年   185篇
  2004年   179篇
  2003年   167篇
  2002年   119篇
  2001年   104篇
  2000年   43篇
  1999年   44篇
  1998年   39篇
  1997年   28篇
  1996年   27篇
  1995年   28篇
  1994年   26篇
  1993年   20篇
  1992年   21篇
  1991年   10篇
  1990年   10篇
  1989年   16篇
  1988年   11篇
  1987年   8篇
  1986年   8篇
  1985年   10篇
  1984年   13篇
  1983年   7篇
  1982年   11篇
  1965年   5篇
  1964年   6篇
  1961年   6篇
  1959年   3篇
  1956年   4篇
  1955年   5篇
  1954年   4篇
排序方式: 共有3953条查询结果,搜索用时 15 毫秒
101.
This article had 2 aims: (a) to comprehensively review and synthesize the literature on predictors of health service utilization in survivors of traumatic events and posttraumatic stress disorder (PTSD) patients and (b) to discuss methodological issues in examining service utilization in this population. PsycINFO was searched for relevant articles published through April 2004. Included studies had to primarily sample trauma survivors or PTSD patients and statistically explore health service use determinants. Although some findings conflicted across studies, increased mental health service use was generally related to being female, having a previous trauma history, and having a PTSD diagnosis. Increased medical service use was found among those with a PTSD diagnosis. Methodological recommendations are made for future health service use studies. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
102.
本文以杨氏双缝干涉实验为基础,讨论了在实验装置的几种变化情况下干涉条纹的变化。  相似文献   
103.
Urbanization process is a major factor of change in the Mediterranean region where pre-urban cities and new urban settlements have raised over the past decades. Several cities rapidly became regional centres or international nodes according to economic and political pressures. Urbanization (and informal settlement) causes land cover changes which can lead to deeper social, economic and environmental changes. The main objective of this paper is to provide time-series information to define and locate the evolution trends of the Tunis Metropolitan Area. In a first step, satellite imagery has been used (1986-1996 SPOT XS) to extract the land cover, identify the urbanization processes and estimate the changes. One of the main aspects is to locate informal settlement areas that grow significantly along the roadway networks in the Tunisian capital. Results show a global progression of the built-up areas of 13% in 10 years. In a second step, the urban growth evolution has been approached by using a potential model that provides general trends of feasible urban expansion, taking into account protection laws of natural and agricultural land. This type of model has not been tested on developing cities and as such it corresponds to a new planning contribution for planners who have no concept of spatially how their urban areas have changed over time and where the growth is occurring. In this case, it has been calibrated over the period of 1986-1996, and then applied to predict the location of the built-up growth over the next 10 years (1996-2006). These results can provide local authorities and other stakeholders with information towards decision support documents for future planning and monitoring plans. Moreover, they can be updated systematically through the integration of remote sensing data.  相似文献   
104.
朱成章 《中国电力》2003,36(9):11-20
介绍世界能源发展现状,未来能源的发展趋向和21世纪的长期能源预测,指出21世界能源具有美好的光明前景。  相似文献   
105.
色彩风景画的写生要把握好风景画的构图关系、整体关系、色彩关系。注重色彩写生的表现形式.充分利用色彩的基本原理。把握光的本质及光与色之间的关系;色相、明度、纯度被称为色彩三要素;要特别重视明暗对比.色彩表现有客观的光学因素,又有主体的认知因素;既有物象的显现因素,又有人的情感因素;既有感性因素。又有理性因素.  相似文献   
106.
Many applications of knowledge discovery and data mining such as rule discovery for semantic query optimization, database integration and decision support, require the knowledge to be consistent with the data. However, databases usually change over time and make machine-discovered knowledge inconsistent. Useful knowledge should be robust against database changes so that it is unlikely to become inconsistent after database updates. This paper defines this notion of robustness in the context of relational databases and describes how robustness of first-order Horn-clause rules can be estimated. Experimental results show that our estimation approach can accurately identify robust rules. We also present a rule antecedent pruning algorithm that improves the robustness and applicability of machine discovered rules to demonstrate the usefulness of robustness estimation.  相似文献   
107.
This paper demonstrates that multitemporal satellite SAR images are most suitable for monitoring the rapid changes of cultivation systems in a subtropical region. A new method is proposed by applying case-based reasoning (CBR) techniques to the classification of SAR images. Stratified sampling is carried out to collect the cases so that the variations of backscatters within a class can be appropriately captured. The use of discrete cases can conveniently represent the internal changes of a class under complicated situations, such as spatial changes in soil conditions and terrain features. These spatial variations are difficult to represent by using rules or mathematical equations. The proposed method has better classification performance than supervised classification methods in the study area. The case library is reusable for time-independent classification when the SAR images are acquired at the same time of the crop growth cycles for different years. The proposed method has been tested in the Pearl River Delta in South China.  相似文献   
108.
黄河冲淤特性"相对清水冲刷、相对浑水淤积"   总被引:1,自引:0,他引:1  
本文回顾总结了以往对黄河干支流河道冲淤特性的研究情况 ,利用所提出的冲淤临界流量与含沙量的关系与渭河下游、黄河下游进行了对比。以此为基础 ,勾画出了黄河干支流冲积河道“相对清水冲刷、相对浑水淤积”的物理图景 ,提出了多沙河流“相对清水冲刷、相对浑水淤积”的冲淤特性  相似文献   
109.
玉米根系几何造型研究   总被引:13,自引:1,他引:13  
通过对玉米根系形态建成过程根系的结构、生长及分布特点和规律观测研究,构建了描述玉米根系形态变化的数学模型。结合粒子系统和计算机图形学技术,在计算机上实现了玉米根系生长的三维显示。其结果和实际的玉米根系的生长发育过程基本一致,为农学研究者提供了一个可视化的根系模型。本模型结构简单、可交互、真实感强,可以较好地虚拟玉米根系的生长过程。  相似文献   
110.
The paperis studied and probed into the cerium application in the passivators of red copper. Through the experimentation of single factor we knoew that ithas remarkable quality influence among red copper passivators by Ce3 , determined that there is obvious function in its small content. And we educed a best technology through the orthogonal test. Research shows: there are obvious changes in the molecular structure of the passivating films after adding the Ce compounds and anticorrosive performance is improved.  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