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   29568篇
  免费   3246篇
  国内免费   1900篇
电工技术   2090篇
综合类   2271篇
化学工业   4558篇
金属工艺   1352篇
机械仪表   3368篇
建筑科学   1331篇
矿业工程   701篇
能源动力   1481篇
轻工业   768篇
水利工程   557篇
石油天然气   1522篇
武器工业   345篇
无线电   2033篇
一般工业技术   2700篇
冶金工业   873篇
原子能技术   133篇
自动化技术   8631篇
  2024年   112篇
  2023年   448篇
  2022年   724篇
  2021年   967篇
  2020年   975篇
  2019年   861篇
  2018年   860篇
  2017年   1052篇
  2016年   1230篇
  2015年   1343篇
  2014年   1880篇
  2013年   1936篇
  2012年   1902篇
  2011年   2508篇
  2010年   1734篇
  2009年   1942篇
  2008年   1901篇
  2007年   2184篇
  2006年   1784篇
  2005年   1585篇
  2004年   1323篇
  2003年   1163篇
  2002年   908篇
  2001年   724篇
  2000年   613篇
  1999年   429篇
  1998年   332篇
  1997年   251篇
  1996年   190篇
  1995年   163篇
  1994年   134篇
  1993年   120篇
  1992年   104篇
  1991年   82篇
  1990年   60篇
  1989年   56篇
  1988年   24篇
  1987年   17篇
  1986年   21篇
  1985年   16篇
  1984年   14篇
  1983年   3篇
  1982年   8篇
  1981年   2篇
  1980年   5篇
  1979年   4篇
  1978年   2篇
  1977年   5篇
  1975年   3篇
  1951年   6篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
矿业软件在矿产储量评价中的应用   总被引:8,自引:0,他引:8  
矿产储量评价的基本内容是建立矿床地质模型进行品位估计和储量分类分级.地质控制条件限制是矿床建模的重要手段。地质统计学方法是矿块品位估计以及储量分级等的有效方法.国内的应用实例表明。国际先进矿业软件是矿产储量评价的先进工具,应用矿业软件进行矿产储量评价是市场经济的需要。  相似文献   
82.
集过程实时监测、系统建模、优化和控制等各层次功能于一体的工业生产过程自动化成为工业界的关注热点之一.从系统建模入手,分析了数学建模的过程及其在冶金领域的应用,由此引出自适应控制系统在工业领域的应用和发展,以显示了这种方法在流程工业自动化中的良好前景.  相似文献   
83.
针对三维实体设计的特点,分析机械制图课程学习三维实体造型技术的必要性及三维实体造型技术对机械制图教学的影响,指出应以三维实体造型技术构建全新的机械制图课程教学体系.  相似文献   
84.
In order to unclose the dynamics of SPS densification, a special sintering sample (Cul Ti wires compact) was designed. Characters of the shrinkage rates during sintering process and mierostructures of products fabrieated by the spark plasma sintering( SPS ) and hot-press .sintering were investigated. The experimental results reveal that a higher temperature field is formed at the connected area and conductive net of the compact. These high-temperature parts deformed more easily than other parts, which is believed to be the main cause of SPS fast densification, according to a hard-core and soft-hell material model.  相似文献   
85.
Regional Geological Information System combines the multi-dimensional and dynamic spatial information into an integrated spatial information system. 3D geological modeling and its preprocessing or post-processing are the most difficult problems for constructing the system. Based on the current 3D GIS technique, some basic problems in establishing the system are discussed in this paper, including 3D spatial data model, 3D geological modeling, and visualization of 3D geological data. A kind of 3D vector data model based on boundary representation for geological object and its topology was developed in order to model and visualize complex geological structures. In addition, some key techniques are pointed out for further study.  相似文献   
86.
The authors tested a model of the relations among adolescents' perceptions of parents', teachers', and classmates' support for, valuing of, and beliefs about their competence in math/science; adolescents' own academic self-perceptions concerning math/science; and their academic performance. The sample included 378 middle school students; 65% were Latino, and 21% were European American. Reflected appraisals of adults' beliefs concerning both the importance of and students' competence in math/science, as well as perceived support, predicted students' own self-perceived importance, competence, scholastic behavior, and performance in these courses. Latino students reported lower mean levels of perceived competence than did European American students (controlling for maternal education). Findings have important implications for understanding achievement socialization in ethnically diverse populations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
87.
Replies to comments made by G. E. Gignac (see record 2005-06671-010) on the current authors' original article (see record 2003-02341-015). Gignac reanalyzed the factor structure of the Mayer-Salovey-Caruso Emotional Intelligence Test (MSCEIT) and found results that differed from those the authors obtained initially. The authors tracked down the surprising sources of those discrepancies. G. E. Gignac's hierarchical model of emotional intelligence appears promising, and the authors anticipate that further investigations of the MSCEIT factor structure may yield additional information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
88.
This article addresses the relation between item recognition and associative (cued) recall. Going beyond measures of performance on each task, the analysis focuses on the degree to which the contingency between successful recognition and successful recall of a studied item reflects the commonality of memory processes underlying the recognition and recall tasks. Specifically, 4 classes of distributed memory models are assessed for their ability to account for the relatively invariant correlation (≈ .5) between successive recognition and recall. Basic versions of each model either under- or overpredict the intertask correlation. Introducing variability in goodness-of-encoding and response criteria, as well as output encoding, enabled all 4 models to reproduce the moderate intertask correlation and the increase in correlation observed in 2 mixed-list experiments. This model-based analysis provides a general theoretical framework for interpreting contingencies between successive memory tests. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
89.
为了解决弓长岭井下在矿体倾角较大、下盘围岩不稳固的情况下矿石回收率低的问题,本文从弓长岭铁矿的实际应用出发,深入研究了放矿口对散体移动规律的影响,在分析模拟系统的设计要求及功能的基础上,对D.Jolley模型进行建模.采用C#开发了计算机模拟系统,模拟实现了大断面出矿的一系列过程。该系统能够对多种方案进行模拟,并对模拟结果进行选优。仿真结果表明大断面进路出矿对提高矿石回收率的正确性及有效性。  相似文献   
90.
This work proposes that the Weibull stress scale parameter, σu, increases with temperature to reflect the increasing microscale toughness of ferritic steels caused by local events that include plastic shielding of microcracks, microcrack blunting, and microcrack arrest. The Weibull modulus, m, then characterizes the temperature invariant, random distribution of microcrack sizes in the material. Direct calibration of σu values at temperatures over the DBT region requires extensive sets of fracture toughness values. A more practical approach developed here utilizes the so-called Master Curve standardized in ASTM Test Method E1921-02 to provide the needed temperature vs. toughness dependence for a material using a minimum number of fracture tests conducted at one temperature. The calibration procedure then selects σu values that force the Weibull stress model to predict the Master Curve temperature dependence of KJc values for the material. At temperatures in mid-to-upper transition, the process becomes more complex as fracture test specimens undergo gradual constraint loss and the idealized conditions of high-constraint, small-scale yielding assumed in E1921-02 gradually degenerate. The paper develops the σu calibration process to incorporate these effects in addition to consideration of threshold toughness effects and the testing of fracture specimens with varying crack-front lengths. Initial illustrations of the calibration process for simpler conditions, i.e. 1T crack-front lengths, use the temperature dependent flow properties and a range of toughness levels for an A533B pressure vessel steel. Then using the extensive fracture toughness data sets for an A508 pressure vessel steel generated recently by Faleskog et al. [Engng. Fract. Mech., in press], the paper concludes with calibrations of both m and σu over the DBT region and assessments of the Master Curve calibration approach developed here.  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