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   40526篇
  免费   265篇
  国内免费   1148篇
电工技术   555篇
综合类   185篇
化学工业   3860篇
金属工艺   1374篇
机械仪表   1935篇
建筑科学   2399篇
矿业工程   1164篇
能源动力   226篇
轻工业   7947篇
水利工程   652篇
石油天然气   918篇
武器工业   182篇
无线电   2420篇
一般工业技术   14461篇
冶金工业   737篇
原子能技术   412篇
自动化技术   2512篇
  2022年   64篇
  2021年   104篇
  2018年   63篇
  2016年   68篇
  2015年   67篇
  2014年   154篇
  2013年   161篇
  2012年   4247篇
  2011年   5402篇
  2010年   1093篇
  2009年   495篇
  2008年   3385篇
  2007年   3193篇
  2006年   2662篇
  2005年   2255篇
  2004年   2018篇
  2003年   1707篇
  2002年   1627篇
  2001年   1291篇
  2000年   1282篇
  1999年   880篇
  1998年   495篇
  1997年   616篇
  1996年   562篇
  1995年   535篇
  1994年   502篇
  1993年   323篇
  1992年   410篇
  1991年   452篇
  1990年   427篇
  1989年   466篇
  1988年   382篇
  1987年   451篇
  1986年   436篇
  1985年   503篇
  1984年   476篇
  1983年   423篇
  1982年   415篇
  1981年   340篇
  1980年   291篇
  1979年   226篇
  1978年   130篇
  1977年   68篇
  1976年   66篇
  1975年   83篇
  1974年   83篇
  1973年   65篇
  1966年   41篇
  1965年   91篇
  1964年   58篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
962.
963.
The crystallization process of the eutectic composition of GdAlO_3-Al_2O_3 from the amorphous phase prepared by rapid-quenching of melt that leads to the formation of a cantaloupe skin-like microstructure was investigated using focused ion-beam scanning electron microscopy (FIB-SEM) and high-resolution transmission electron microscopy (HR-TEM).The amorphous films were heat-treated at temperatures between 1000 °C and 1500 °C for up to 30min to form the eutectic phases of GdAlO_3 and Al_2O_3.The GdAlO_3 and Al_2O_3 crystal phases that formed from the amorphous phase were identified by FIB-SEM and HR-TEM.Both components began to crystallize and grow from the amorphous phase separately at different temperatures.The formation process of these crystal phases was different from that of the ordinary eutectic microstructure solidified from the GdAlO_3-Al_2O_3 system.Therefore,the observed structure is termed "eutectic-like" for distinction.The microstructures formed from the amorphous phases at sufficiently high temperatures consisted of ultra-fine microstructures of individually crystallized components and were similar to ordinary eutectic microstructures.By heat-treating the amorphous films at 1500 °C for either 2 min,8min or 30min,the ultra-fine components of GdAlO_3 and Al_2O_3 were found to crystallize following a eutectic-like stage after 8min of heat treatment.  相似文献   
964.
Computer vision holds great promise for helping persons with blindness or visual impairments (VI) to interpret and explore the visual world. To this end, it is worthwhile to assess the situation critically by understanding the actual needs of the VI population and which of these needs might be addressed by computer vision. This article reviews the types of assistive technology application areas that have already been developed for VI, and the possible roles that computer vision can play in facilitating these applications. We discuss how appropriate user interfaces are designed to translate the output of computer vision algorithms into information that the user can quickly and safely act upon, and how system-level characteristics affect the overall usability of an assistive technology. Finally, we conclude by highlighting a few novel and intriguing areas of application of computer vision to assistive technology.  相似文献   
965.
MoB/CoCr涂层具有较高的耐熔融锌侵蚀的能力,并被广泛地应用于钢铁工业镀锌生产线中[1].然而在实验室测试中,这种涂层有时还没有显示出其原有特性就失效了.研究发现,这些失效的试样往往具有较高的孔隙率,导致了熔融Zn通过孔洞加速渗透对基体钢材产生腐蚀并使涂层脱离.这表明,在实际应用中,高密度涂层对于展现其耐蚀性与保证质量的极度重要性.在本文中,我们通过优化粉末性能并采用JP-5000超音速火焰喷涂制备了高密度MoB/CoCr涂层.我们通过盐雾试验来评估涂层的致密性.最佳密度的涂层在经过300小时的盐雾试验后,其低碳钢基体材料没有发生锈蚀.另一方面,多孔的涂层在经过24~48小时的盐雾试验后,其基体材料出现了锈蚀.经盐雾试验验证的最佳涂层在工业镀锌浴中浸没90天后(>2000小时)没有发生失效.  相似文献   
966.
Polymethoxyflavones (PMFs) extracted from citrus peel exhibit potent anti-cancer activity, but are highly hydrophobic molecules with poor solubility in both water and oil at ambient and body temperature, which limits their bioavailability. The possibility of encapsulating PMFs within nanoemulsion-based delivery systems to facilitate their application in nutraceutical and pharmaceutical products was investigated. The influence of oil type (corn oil, MCT, orange oil), emulsifier type (β-lactoglobulin, lyso-lecithin, Tween, and DTAB), and neutral cosolvents (glycerol and ethanol) on the formation and stability of PMF-loaded nanoemulsions was examined. Nanoemulsions (r < 100 nm) could be formed using high pressure homogenization for all emulsifier types, except DTAB. Lipid droplet charge could be altered from highly cationic (DTAB), to near neutral (Tween), to highly anionic (β-lactoglobulin, lyso-lecithin) by varying emulsifier type. PMF crystals formed in all nanoemulsions after preparation, which had a tendency to sediment during storage. The size, morphology, and aggregation of PMF crystals depended on preparation method, emulsifier type, oil type, and cosolvent addition. These results have important implications for the development of delivery systems for bioactive components that have poor oil and water solubility at application temperatures.  相似文献   
967.
We present an experimental study concerning the flow inside a liquid metal column exposed to a pulsed rotating magnetic field.This paper is aimed at highly resolved,quantitative velocity measurements in the eutectic GalnSn alloy.A novel ultrasound Doppler system was used two measure two-dimensional velocity fields of the secondary flow in the radial-meridional plane.It employs an array of 25 transducer elements allowing a fast electronic traversing with concurrently high spatial and temporal resolution.The measurements revealed transient flow regimes showing distinct inertial oscillations and coherent vortex structures.The results demonstrate that the arising flow structure depends sensitively on the frequency of the RMF pulses.A maximum intensity of a periodic meridional flow can be observed,if the corresponding pulse frequency fp relates to the eigenperiod of the respective inertial mode in a developed regime.The electromagnetic stirring method that uses a modulated RMF offers considerable potential to enhance the stirring efficiency and to optimize the properties of castings by a well-aimed flow control during solidification.  相似文献   
968.
基于更为严厉的甲醛重新分类的背景,TEGEWA协会整理工作组已开发出一种可确定纺织助剂中游离甲醛含量的新方法。目前此法鉴于其统一的程序,可使因不同的内部测试方法而得出不同观点的测试成为过去。  相似文献   
969.
由于焦炉在装煤是会产生在大量烟尘,即使采用了最先进的技术,装煤方法仍是炼焦工业控制污染的关键手段之一,目前,正在实施控制焦米装煤时烟放散新方法的开发计划,现将该计算的第一部分,即平煤方法的改进情况介绍如下。  相似文献   
970.
美国萨维奇拉皮兹(Savage Rapids)坝自1921年动工兴建以来,鱼类如何过坝一直是专家关注的焦点。经研究,最终决定于2006年10月开始拆除这座有88 a历史的大坝。该项工程于2006年10月开工,并于2009年11月完工,随后新建了灌溉分流设施,结果不仅恢复了溯河鱼类通道,而且促进了当地经济发展。  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