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   5015篇
  免费   515篇
  国内免费   544篇
电工技术   347篇
综合类   472篇
化学工业   581篇
金属工艺   93篇
机械仪表   302篇
建筑科学   305篇
矿业工程   198篇
能源动力   198篇
轻工业   475篇
水利工程   231篇
石油天然气   776篇
武器工业   31篇
无线电   328篇
一般工业技术   340篇
冶金工业   192篇
原子能技术   554篇
自动化技术   651篇
  2025年   31篇
  2024年   132篇
  2023年   136篇
  2022年   167篇
  2021年   189篇
  2020年   225篇
  2019年   202篇
  2018年   173篇
  2017年   187篇
  2016年   225篇
  2015年   192篇
  2014年   255篇
  2013年   446篇
  2012年   309篇
  2011年   328篇
  2010年   265篇
  2009年   218篇
  2008年   217篇
  2007年   250篇
  2006年   263篇
  2005年   236篇
  2004年   214篇
  2003年   198篇
  2002年   130篇
  2001年   141篇
  2000年   108篇
  1999年   91篇
  1998年   77篇
  1997年   70篇
  1996年   56篇
  1995年   60篇
  1994年   62篇
  1993年   34篇
  1992年   35篇
  1991年   31篇
  1990年   24篇
  1989年   19篇
  1988年   16篇
  1987年   13篇
  1986年   9篇
  1985年   8篇
  1984年   3篇
  1983年   2篇
  1981年   9篇
  1980年   4篇
  1977年   2篇
  1976年   1篇
  1975年   2篇
  1974年   1篇
  1959年   7篇
排序方式: 共有6074条查询结果,搜索用时 15 毫秒
41.
Cr17Ni2钢焊接接头抗刀状腐蚀性能的研究   总被引:1,自引:0,他引:1  
采用二次稳定化退火处理,解决了Cr17Ni2钢异质焊接接头刀状腐蚀的问题。提高了用Cr17Ni2钢制造的焊接叶轮的使用寿命,取得了明显的经济效益。  相似文献   
42.
Ammonia synthesis: The bellwether reaction in heterogeneous catalysis   总被引:1,自引:0,他引:1  
This is a personal account of the Havreholm Conference with a choice of topics dealing with catalytic ammonia synthesis. Among the general concepts that were retained are: the rate determining step with rates of adsorption and desorption of nitrogen; the direct activated dissociative adsorption of N2; the surface crystalline anisotropy of iron; the role of promoters in industrial iron based catalysts; and the atomic structure of the metallic surface on the industrial multiply promoted catalyst. Finally, a new isotope jump technique to measure an upper limit to the real turnover frequency is discussed.  相似文献   
43.
Impregnating resins in fusion magnet technology are required to be radiation stable, low viscosity, long usable life and high toughness. To meet these objectives, we developed a new epoxy based composite which consists of triglycidyl-p-aminophenol (TGPAP) epoxy resin and isopropylidenebisphenol bis[(2-glycidyloxy-3-n-butoxy)-1-propylether] (IPBE). The ratio of TGPAP to IPBE can be varied to achieve desired viscosity and working time. The boron-free glass fiber reinforced composites were prepared by vacuum pressure impregnation. The radiation resistance was evaluated by 60Co γ-ray irradiation of 1 MGy at ambient temperature. The mechanical properties of the composites have been measured at room temperature and at 77 K.  相似文献   
44.
介绍了BA/Py,BA/Ph和PHBA三种具有三芳基甲烷结构B阶树脂的合成方法及分子链的单元结构形式。对用紫外光和激光照射法进行脱氢反应的实验条件及脱氢化后树脂的磁性能(磁滞现象,矫顽力和磁化强度)进行考查。  相似文献   
45.
Galvanostatic electrochemical oxidation of dimethylsulphoxide (DMSO) to dimethylsulfone (DMSO2) has been effected at a dimensionally stable anode (DSA) under different conditions of current density and reaction media, in both a batch and a flow reactor (membrane cell with an ion-exchange membrane between the two working electrodes) functioning in batch recirculation mode. Excellent yields of the sulfone have been obtained under both conditions. The product has been characterized by various physicochemical techniques. The operational conditions giving maximum yield of the product have been established. The electrochemical oxidation of DMSO has also been studied by cyclic voltammetry at a glassy carbon (GC) electrode. The mechanism of electrochemical oxidation and the advantages of the present methods over existing ones, are discussed.  相似文献   
46.
    
In this paper, a framework to construct higher‐order‐accurate time‐step‐integration algorithms based on the post‐integration techniques is presented. The prescribed initial conditions are naturally incorporated in the formulations and can be strongly or weakly enforced. The algorithmic parameters are chosen such that unconditionally A‐stable higher‐order‐accurate time‐step‐integration algorithms with controllable numerical dissipation can be constructed for linear problems. Besides, it is shown that the order of accuracy for non‐linear problems is maintained through the relationship between the present formulation and the Runge–Kutta method. The second‐order differential equations are also considered. Numerical examples are given to illustrate the validity of the present formulation. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   
47.
    
The presence of stable foams can seriously impair the ability of an activated sludge to produce a high-quality effluent. This paper examines how the physicochemical characteristics of the solids are related to foam formation and describes how the foaming potential of full-scale plants can be assessed. It also confirms that Microthrix parvicella can exhibit a variable morphology and shows that these variations are related to the physicochemical properties that characterize foam-forming solids.  相似文献   
48.
块H-矩阵的简捷判据   总被引:4,自引:0,他引:4  
Feingold与Varga引入了块对角占优的概念,基于它的优美性质,引起了许多学者的浓厚兴趣本文研究块H-矩阵(广义块对角占优矩阵)的实用判定,给出了块H-矩阵的两个新的简捷判据,并应用十矩阵正稳定性和亚正定性的判定。  相似文献   
49.
50.
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