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   60154篇
  免费   6956篇
  国内免费   3212篇
电工技术   2878篇
技术理论   5篇
综合类   4390篇
化学工业   21441篇
金属工艺   2624篇
机械仪表   1834篇
建筑科学   3136篇
矿业工程   707篇
能源动力   8072篇
轻工业   3857篇
水利工程   783篇
石油天然气   2535篇
武器工业   466篇
无线电   3477篇
一般工业技术   7116篇
冶金工业   2338篇
原子能技术   1499篇
自动化技术   3164篇
  2024年   303篇
  2023年   1535篇
  2022年   2152篇
  2021年   2374篇
  2020年   2430篇
  2019年   2276篇
  2018年   2012篇
  2017年   2177篇
  2016年   2153篇
  2015年   2080篇
  2014年   3111篇
  2013年   3842篇
  2012年   3637篇
  2011年   4103篇
  2010年   3076篇
  2009年   3188篇
  2008年   2951篇
  2007年   3568篇
  2006年   3242篇
  2005年   2966篇
  2004年   2498篇
  2003年   2277篇
  2002年   1937篇
  2001年   1618篇
  2000年   1410篇
  1999年   1156篇
  1998年   1011篇
  1997年   864篇
  1996年   762篇
  1995年   651篇
  1994年   553篇
  1993年   453篇
  1992年   400篇
  1991年   273篇
  1990年   255篇
  1989年   201篇
  1988年   153篇
  1987年   124篇
  1986年   86篇
  1985年   74篇
  1984年   92篇
  1983年   52篇
  1982年   38篇
  1981年   15篇
  1980年   19篇
  1966年   10篇
  1964年   11篇
  1959年   20篇
  1957年   9篇
  1951年   50篇
排序方式: 共有10000条查询结果,搜索用时 22 毫秒
81.
分子内敏化鎓盐的合成及光敏性研究   总被引:3,自引:0,他引:3  
二芳基碘鎓盐和三芳基硫鎓盐是阳离子聚合的光引发剂和光敏产酸物,但他们在300nm以上的光吸收很低,限制了对紫外光的利用效率。为解决此问题,本文合成了一些新的碘鎓盐和硫鎓盐,并用凝胶时间方法考察了它们的光引发效率。实验结果表明,2-苯硫基甲基,2′,4′-二甲基二苯碘鎓盐和9-蒽丙基,二苯基硫鎓盐具有特别高的光引发效率,这归之于光照时这些鎓盐发生了分子内电荷转移反应,即发生了分子内敏化。9-蒽丙基二苯硫鎓盐分子中的蒽基(An)是电子给体也是敏化基团,光照时可发生如下反应:  相似文献   
82.
Based on experimental results concerning the compressive strength development of concrete containing fly ash, the authors derived an estimation equation for compressive strength development. The equation can express coefficient , which indicates the activity of fly ash as a binder, in the form of a function of age, fly-ash content, and Blaine specific surface area of fly ash.

This equation is capable of explaining the increases in the early strength due to fly ash in place of part of fine aggregate, the decreases in the early strength due to fly ash in place of part of cement, the increases in the long-term strength due to pozzolanic reaction, the relationship between the fly-ash replacement ratio and the ratio of strength increase/decrease, and the effect of fly ash's Blaine specific surface area on the strength.  相似文献   

83.
84.
高杰  单凤君 《辽宁化工》2004,33(7):393-395
研究为在炼油污水的CAST工艺的主反应区中 ,通过恰当控制pH值和DO(污水中溶解氧含量 )值 ,可以使硝化与反硝化反应同步进行 ,在去除COD ,BOD的同时 ,也可提高其脱氮效果 ,从而得出DO的最佳值为 0 .8mg/L ,pH为 7.3~ 7.7之间。  相似文献   
85.
介绍了月桂氮草酮作为高效皮肤促渗剂的发展概况、合成工艺、研究进展及其应用前景。  相似文献   
86.
Horizontal pipeline and tubular loop aerators are of interest for fermentation and waste water treatment and are ideally suited for continuous processing. A major drawback is that these pipeline contactors invariably operate in the “elongated bubble and plug” regime in which the mass transfer rate is low. This article evaluates the performance of a horizontal pipeline aerator fitted with nozzles equispaced along its length to enhance mass transfer rates by promoting turbulence and augmenting effective interfacial area. Such devices can also be advantageously used in long pipe lines as in the case of treating waste while it is being transported. Pressure drop and overall liquid-side mass transfer coefficient data are reported as functions of liquid (water) and gas flow rates and nozzle size and spacing. It is shown that for all the conditions studied, kLa = 0.026(ΔP/L)1.036 and that the pressure gradient is given by a simple correlation, provided an empirical parameter which characterises a nozzle is known. Preliminary investigations on the effect of surfactant ad the presence of suspended solids (size 75 μm) on mass transfer coefficient are also reported. Very high values of power dissipation can be achieved in such aerators without mechanically moving parts and high values of mass transfer coefficient can be realized.  相似文献   
87.
Worldwide, cervical cancer is the second most common cancer in women, after breast cancer. The prevalence of this malignant disease is estimated at 1.4 million cases worldwide, causing about 290,000 deaths and 500,000 new cases per year, of which 80% correspond to women living in developing countries. In this work we propose a family of ordered models for basal cells of the cervix corresponding to different stages ranging from normal cells to the formation of precancerous lesions. We analyse the first member of the family analytically and for the second member we developed a non-standard numerical method in order to extract some biological information.  相似文献   
88.
Axisymmetrical, two dimensional mass transfer in a tube and a through-hole was studied. The elliptic convective-diffusion equation was solved numerically by taking into account both the axial and radial diffusion in the entrance region of an infinite tube. The whole mass-transfer region in a tube of finite length was also studied by dividing the domain into several regions according to different mass-transfer mechanisms. A similar analysis is then conducted for a through-hole geometry by assuming a modified Hagen-Poiseuille fluid pattern. Results show that mass-transfer rate in a through-hole is larger than that in a tube by approximately 10%. This is due primarily to faster fluid flow within the concentration boundary layer in a through-hole.  相似文献   
89.
从反应注射成型过程对混合器的结构设计、操作条件等的要求出发,对碰撞式混合器的设计和使用应注意的问题进行了分析探讨,并提出了相应的解决办法和处理措施。  相似文献   
90.
The velocity of the chain explosivedecomposition reaction in silver azide whiskes has been measured (1500 m/sec). The measured velocity is identified as the propagation velocity of the diffusion front of holes generated in the course of explosive decomposition.  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