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   1190篇
  免费   96篇
  国内免费   38篇
电工技术   29篇
综合类   43篇
化学工业   236篇
金属工艺   42篇
机械仪表   59篇
建筑科学   54篇
矿业工程   14篇
能源动力   39篇
轻工业   148篇
水利工程   14篇
石油天然气   57篇
武器工业   5篇
无线电   101篇
一般工业技术   173篇
冶金工业   76篇
原子能技术   27篇
自动化技术   207篇
  2024年   4篇
  2023年   13篇
  2022年   27篇
  2021年   65篇
  2020年   36篇
  2019年   32篇
  2018年   50篇
  2017年   63篇
  2016年   43篇
  2015年   43篇
  2014年   56篇
  2013年   92篇
  2012年   94篇
  2011年   89篇
  2010年   65篇
  2009年   54篇
  2008年   61篇
  2007年   59篇
  2006年   50篇
  2005年   51篇
  2004年   34篇
  2003年   34篇
  2002年   13篇
  2001年   17篇
  2000年   21篇
  1999年   22篇
  1998年   27篇
  1997年   16篇
  1996年   21篇
  1995年   14篇
  1994年   9篇
  1993年   6篇
  1992年   7篇
  1991年   9篇
  1990年   2篇
  1989年   4篇
  1988年   4篇
  1987年   2篇
  1985年   2篇
  1984年   2篇
  1982年   1篇
  1981年   1篇
  1980年   1篇
  1977年   2篇
  1976年   2篇
  1973年   2篇
  1971年   1篇
  1962年   1篇
排序方式: 共有1324条查询结果,搜索用时 125 毫秒
11.

Numerous visual notations are present in technical and business domains. Notations have to be cognitively effective to ease the planning, documentation, and communication of the domains’ concepts. Semantic transparency (ST) is one of the elementary principles that influence notations’ cognitive effectiveness. However, the principle is criticized for not being well defined and challenges arise in the evaluations and applications of ST. Accordingly, this research’s objectives were to answer how the ST principle is defined, operationalized, and evaluated in present notations as well as applied in the design of new notations in ICT and related areas. To meet these objectives, a systematic literature review was conducted with 94 studies passing the selection process criteria. The results reject one of the three aspects, which define semantic transparency, namely “ST is achieved with the use of icons.” Besides, taxonomies of related concepts and research methods, evaluation metrics, and other findings from this study can help to conduct verifiable ST-related experiments and applications, consequently improving the visual vocabularies of notations and effectiveness of the resulting diagrams.

  相似文献   
12.
在构建通货膨胀与RPV关系理论模型的基础上,运用面板数据固定效应估计量来检验中国通货膨胀对RPV影响的长期效应,并构建向量误差修正模型来分析中国通货膨胀对RPV影响的短期效应.研究得出,在不考虑确定性因素和外生变量的情况下,从全国来看,总体是短期效应大于长期效应;相反则是长期效应略大于短期效应.在上述两种情况下,各地区的长期效应与短期效应也明显不同.因此,国家应该多考虑不同地区通货膨胀对RPV影响的长期效应与短期效应大小,从而有效地治理通货膨胀和稳定物价水平.  相似文献   
13.
丹东港是中国海岸线最北端的不冻良港,近年来从该口岸进境的大豆数量逐年增加,从2009年至今,丹东港约有280万吨大豆进境,主要来自美国和巴西。从进口大豆检出杂草情况看,杂草种类繁多,共17科、74种,其中检疫性杂草有5科、11种。本文对丹东港进口大豆携带的杂草进行了分类与风险分析,并提出相应的一些建议,从而降低有害生物的传入几率。  相似文献   
14.
In this paper, the boron-containing mesoporous bioactive glass (MBG) nanospheres have been successfully synthesized by modified sol-gel method assisted by surfactant, and the effect of boron substitution on structure and bioactivity was evaluated by combining experiments and ab initio molecular dynamics (AIMD) simulations. All of the samples exhibit regularly uniform mesoporous spherical microstructure with an average size of about 60 nm, and the boron-containing MBGs show higher specific surface area with the value up to 416.20 m2/g. The simulated body fluid (SBF) immersion test confirms that the deposited hydroxyapatite (HA) evidently increases with the increasing of boron content, indicating that the biological behavior has been significantly improved resulting from incorporation of boron. Additionally, our results also reveal that B2O3 substitution has positive impact on cell proliferation of human periodontal ligament cells (hPDLCs) at lower extracted concentration. Furthermore, AIMD simulation is employed to understand the relationship between structural changes and in vitro bioactivity in terms of structural information, especially the boron coordination number. The results illustrate that the boron-containing MBG nanospheres with excellent bioactivity are great potential for biomedical applications.  相似文献   
15.
W.J. Kim  Y.K. Sa  J.B. Lee  H.G. Jeong 《Intermetallics》2006,14(12):1391-1396
Superplastic deformation and crystallization behavior of a Cu54Ni6Zr22Ti18 metallic glass were investigated. A maximum elongation of 650% was obtained at 733 K at 1 × 10−2 s−1 from the sheet fabricated by squeeze copper-mold casting method. At low strain rates, the strain-rate-sensitivity exponent value was close to 1, suggesting that Newtonian-like behavior governed the plastic flow. At a high strain rate around 10−2 s−1, a transition from Newtonian to non-Newtonian behavior took place with decrease in m value. Large strain hardening by crystallization occurred during the course of deformation. The strain hardening was found to be caused by crystallization according to the analyses of the relation of true stress vs. testing time, T-T-T diagram and DSC characteristics. The time periods up to the strain before strain hardening at 733 K for the Cu54Ni6Zr22Ti18 metallic glass were similar to that of the Zr65Al10Ni10Cu15 metallic glass at 696 K as 180–300 s (3–5 min). This coincidence could be explained by comparison of their T-T-T diagrams showing that the incubation times for crystallization of the Cu BMG at 733 K and for Zr BMG at 696 K are similar.  相似文献   
16.
铸铁坩锅抗铝融蚀等离子喷涂技术   总被引:1,自引:1,他引:1  
针对提高化铝用铸铁坩埚抗融蚀寿命的实际问题,选用价格较低、耐高温、抗融蚀性好的Al2O3陶瓷材料作为坩埚内壁的工作层,采用等离子喷涂技术来提高其抗融蚀性。但由于Al2O3陶瓷涂层的致密性差、结合强度及抗热震寿命低等缺点,不适宜化铝坩埚在720℃长时间加温,且液铝呈搅拌行为的工作条件下使用。本文在Al2O3喷涂粉末中加入13%TiO2,促使涂层的组织结构发生变化,提高了涂层的结合强度,改善了涂层的致  相似文献   
17.
研究了复合稀土氧化物-钼-铼金属陶瓷阴极的二次电子发射系数和抗暴露大气性能,对发射后的表面进行了表面分析,并与单元、复合稀土-钼金属陶瓷阴极进行了对比.研究结果表明:加入微量铼的复合稀土氧化物-钼金属陶瓷阴极的二次电子发射系数可提高8%,其最大次级发射系数δm为2.65,且具有较好的抗暴露大气性能.  相似文献   
18.
19.
20.
Occurrence of occlusion while providing visual surveillance leads to anarchy as the track of the subject under motion may be lost. This often results into the failure of the surveillance system. The approach of predicting motion of moving subjects and hence the chances of their mutual occlusion gives an upper hand to surveillance system to take in-time necessary action towards mitigation of loss of track during dynamic occlusion. Direction of motion of a moving subject plays a major role while studying its motion. Direction along with the velocity of a subject in a 3D plane completely describes the motion of any subject. This article proposes a model‘-based approach for direction prediction of a moving subject in a 3D global plane as acquired in a 2D camera plane. The proposed approach uses the eight discrete directions of motion as proposed in and models different directions. The proposed direction prediction method is experimentally verified with six different classifiers, i.e. regression analysis, simple logistic regression, MLP, k-NN, SVM and Bays classifier over existing as well as self-acquired databases. The initial simulation results are motivating as the overall accuracies achieved through different classifiers are of the range of 87–94 \(\%\), which advocates the suitability of the said approach.  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