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   28901篇
  免费   3629篇
  国内免费   2033篇
电工技术   2587篇
综合类   3231篇
化学工业   2589篇
金属工艺   558篇
机械仪表   1779篇
建筑科学   3439篇
矿业工程   436篇
能源动力   1053篇
轻工业   5021篇
水利工程   818篇
石油天然气   954篇
武器工业   353篇
无线电   2081篇
一般工业技术   3509篇
冶金工业   1307篇
原子能技术   495篇
自动化技术   4353篇
  2024年   180篇
  2023年   595篇
  2022年   1403篇
  2021年   1411篇
  2020年   1341篇
  2019年   1209篇
  2018年   1073篇
  2017年   1281篇
  2016年   1317篇
  2015年   1399篇
  2014年   1719篇
  2013年   1976篇
  2012年   2451篇
  2011年   2516篇
  2010年   1615篇
  2009年   1569篇
  2008年   1421篇
  2007年   1597篇
  2006年   1412篇
  2005年   1170篇
  2004年   941篇
  2003年   779篇
  2002年   613篇
  2001年   550篇
  2000年   445篇
  1999年   384篇
  1998年   349篇
  1997年   268篇
  1996年   223篇
  1995年   212篇
  1994年   166篇
  1993年   150篇
  1992年   125篇
  1991年   91篇
  1990年   82篇
  1989年   62篇
  1988年   54篇
  1987年   41篇
  1986年   33篇
  1985年   33篇
  1984年   30篇
  1983年   15篇
  1982年   22篇
  1980年   24篇
  1979年   22篇
  1965年   15篇
  1964年   19篇
  1963年   17篇
  1961年   13篇
  1957年   14篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
The authors used visual search tasks in which components of the classic flanker task (B. A. Eriksen & C. W. Eriksen, 1974) were introduced. In several experiments the authors obtained evidence of parallel search for a target among distractor elements. Therefore, 2-stage models of visual search predict no effect of the identity of those distractors. However, clear compatibility effects of the distractors were obtained: Responses were faster when the distractors were compatible with the response than when they were incompatible. These results show that even in parallel search tasks identity information is extracted from the distractors. In addition, alternative interpretations of the results in terms of the occasional identification of a distractor before or after the target was identified could be ruled out. The results showed that flat search slopes obtained in visual search experiments provide no benchmark for preattentive processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
82.
Understanding how aging influences cognition across different cultures has been hindered by a lack of standardized, cross-referenced verbal stimuli. This study introduces a database of such item-level stimuli for both younger and older adults, in China and the United States, and makes 3 distinct contributions. First, the authors specify which item categories generalize across age and/or cultural groups, rigorously quantifying differences among them. Second, they introduce novel, powerful methods to measure between-group differences in freely generated ranked data, the rank-ordered logit model and Hellinger Affinity. Finally, a broad archive of tested, cross-linguistic stimuli is now freely available to researchers: data, similarity measures, and all stimulus materials for 105 categories and 4 culture-by-age groups, comprising over 10,000 fully translated unique item responses. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
83.
A modified rainflow counting method   总被引:1,自引:0,他引:1  
The rainflow counting method is commonly recognized to be a good cyclic counting method in fatigue life prediction and for testing engineering components and structures. However, it has some shortcomings, which are pointed out in this paper in connection with the analysis of the stress-strain response. A modified rainflow counting method is presented. Case studies show that all the cycles really existing in the stress-strain response that cannot be counted by the rainflow counting method can be counted by the modified rainflow counting method. So it can be said that the modified rainflow counting method is a more reasonable cycling counting method than the traditional rainflow counting method.  相似文献   
84.
正压冲固基础海洋平台冰激振动动力响应   总被引:1,自引:0,他引:1  
陈荣  王德禹 《石油机械》2006,34(3):20-23
正压冲固基础海洋平台是一种新型平台桩基结构形式。采用三维有限元的数值分析方法,建立了正压冲固平台的三维有限元模型。基于冰激强迫振动理论提出动冰载荷的计算方法,根据海冰破碎长度和冰速确定冰载周期,冰强度限制的水平冰力作为冰力峰值,得到的动冰载荷用于正压冲固平台的动力响应分析,并依照规范计算了6倍桩径处刚性固定时的动力响应。三维有限元方法计算得到的动力响应大于6倍桩径刚性固定时的计算结果,结构安全性评估偏于安全。  相似文献   
85.
Due to clearly distinguishable damage symptoms, it is differentiated between the surface and sub‐surface failure mode of rolling bearings. Material states red out by X‐ray diffraction (XRD) residual stress measurements point to a variety of loading conditions especially at raceway surfaces that are associated with several competing failure mechanisms. The corresponding lifetime reduction can range from the lower fatigue strength region to material ratcheting in extreme cases. Relevant position of the microstructural changes and nature of the failure mechanisms are characterized. The time alteration of the XRD material parameters measured at or near the surface and at the depth of the maximum equivalent stress correlates, in a different manner, with the statistical parameter of the 10 % bearing life. Both failure modes are illustrated by concrete examples. Contaminated lubricant and boundary lubrication, which represent practically important surface‐induced failures, are discussed in more detail. Gray staining, i.e. shallow pitting, often occurs without distinct indication of global material aging by means of XRD characteristics. Here, scanning electron microscopy observations and electron microprobe analyses point to corrosion fatigue as acting surface failure mechanism. The interaction between material and lubricant under complex loading regimes particularly of mixed friction and corrosion opens further failure research areas in the field of tribology.  相似文献   
86.
Performance on antisaccade trials requires the inhibition of a prepotent response (i.e., don't look at the flashing cue) and the generation and execution of a correct saccade in the opposite direction. The authors attempted to further specify the role of working memory (WM) span differences in the antisaccade task. They tested high- and low-span individuals on variants of prosaccade and antisaccade trials in which an eye movement is the sole requirement. In 3 experiments, they demonstrated the importance of WM span differences in both suppression of a reflexive saccade and generation of a volitional eye movement. The results support the contention that individual differences in WM span are not exclusively due to differences in inhibition but also reflect differences in directing the focus of attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
87.
Original studies on gust factor buffeting dealt with the alongwind displacement of structures. Research on this topic carried out since the nineties followed two distinct lines: the first determines the maximum effects due to the alongwind response; the second extends the original method from the alongwind response to crosswind and torsional responses. This paper represents the junction point of these research lines with reference to cantilever slender vertical structures. It derives the most relevant effects associated with the three-dimensional (3-D) wind-excited response of this structural type and shows that a suitable definition of one non-dimensional quantity, referred to as the 3-D gust effect factor, provides such effects at any level through a wide set of experimental, numerical and analytical procedures. A new definition of a 3-D equivalent static force consistent with this method is also introduced and critically compared with previous analogous statements.  相似文献   
88.
MITI has actively done R&D on industrial technology for waste and reclamation and so there are many research items from small scale to large scale. However, Ecofactory and researches on recycling of metallic materials are introduced here. Ecofactory was proposed by the Mechanical Engineering Laboratory and is now at the stage of the Leading Research, a new research scheme in AISt. Researches on recycling of metallic materials are being done with subsidy. Those researches should contribute to both the preservatin of the global environment and effective recycling of waste materials.Abbreviations AIST Agency of Industrial Science and Technology - MITI Ministry of International Trade and Industry - NEDO New Energy and Industrial Technology Development Organization  相似文献   
89.
A centrifugal partition chromatograph (CPC) was used as a liquid-liquid catalytic reactor for the isomerisation of hexen-3-ol into ethylpropylketone with a water soluble rhodium catalyst. Global mass transfer coefficients were measured and shown to depend on both the nature of the solute and the flow rate. Liquid-liquid partition isotherms were also determined with the CPC using elution chromatography. Finally, a reactor model was derived to account for the experimental results obtained both under stationary and transient (pulse) conditions. A parameter sensitivity evaluation is also presented.  相似文献   
90.
The effects of various stearic-palmitic acid blend concentrations in films, storage temperatures and storage times on potato chip quality were evaluated using Response Surface Methodology. Storage temperature and time affected the quality of potato chips. The maximum storage times for acceptable potato chip quality were: 30 to 43 days, 23 to 25 days, and 11 to 12 days for storage temperatures of 15, 25 and 35°C, respectively. Results were independent of stearic-palmitic acid blend concentrations.  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