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   78924篇
  免费   7365篇
  国内免费   4625篇
电工技术   5064篇
技术理论   4篇
综合类   6328篇
化学工业   12819篇
金属工艺   4307篇
机械仪表   4641篇
建筑科学   6633篇
矿业工程   2392篇
能源动力   2356篇
轻工业   6475篇
水利工程   1574篇
石油天然气   4315篇
武器工业   563篇
无线电   8713篇
一般工业技术   8626篇
冶金工业   3452篇
原子能技术   1012篇
自动化技术   11640篇
  2024年   404篇
  2023年   1449篇
  2022年   2501篇
  2021年   3407篇
  2020年   2585篇
  2019年   2375篇
  2018年   2496篇
  2017年   2746篇
  2016年   2355篇
  2015年   3243篇
  2014年   4006篇
  2013年   4704篇
  2012年   4961篇
  2011年   5353篇
  2010年   4842篇
  2009年   4543篇
  2008年   4520篇
  2007年   4173篇
  2006年   4032篇
  2005年   3408篇
  2004年   2735篇
  2003年   3081篇
  2002年   3908篇
  2001年   3289篇
  2000年   2039篇
  1999年   1695篇
  1998年   1104篇
  1997年   995篇
  1996年   917篇
  1995年   735篇
  1994年   622篇
  1993年   422篇
  1992年   362篇
  1991年   211篇
  1990年   178篇
  1989年   119篇
  1988年   114篇
  1987年   64篇
  1986年   52篇
  1985年   38篇
  1984年   36篇
  1983年   22篇
  1982年   18篇
  1981年   16篇
  1980年   19篇
  1979年   8篇
  1965年   1篇
  1959年   7篇
  1951年   4篇
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
21.
秦宝光 《玻璃》2003,30(6):30-33
从能源、市场和效益角度入手,浅显分析了玻璃企业现状,提出了企业应根据市场变化调整决策,利用现代资 本市场建立现代化企业制度,将油价大幅上升做为企业获取巨额利润的重大机遇,保持企业稳步长久发展。  相似文献   
22.
Aqueous yttria-stabilized zirconia slurry was cast on a substrate to form wet coatings. Both weight loss and thickness reduction were measured, during the drying process. Lateral drying was observed by in situ monitoring of the coating surface. The drying kinetics were classified as an initial constant rate period (CRP), followed by a falling rate period (FRP). Thickness reduction occurred in the CRP stage, and was uneven across the coating because of lateral flow. As tensile stresses developed within the coating because of the constrained volume shrinkage, crack formation and propagation occurred in the FRP stage and affected the drying rate.  相似文献   
23.
简要介绍了推力矢量控制技术的概念,分析了推力矢量控制的基本原理及特点.在简要分析其技术发展历程的基础上,给出了导弹推力矢量技术的现状和发展趋势.  相似文献   
24.
BACKGROUND: Carboxylic acids are among the most important substances that can be manufactured from biomass. However, the recovery of carboxylic acids from fermentation broths presents a challenging separation problem. To avoid the production of waste salts and net consumption of chemicals in the calcium carboxylate salt process, the use of reversible chemical complexation with polymeric sorbents and extractants is attractive for carboxylic acid recovery. Pyruvic acid is widely used in the manufacture of medicines, pesticides and foodstuffs and can be produced by fermentation. Since the acidity of pyruvic acid (pKa = 2.49) is stronger than that of normal carboxylic acids, and as few reports on the recovery of pyruvic acid are available, the sorption of pyruvic acid from aqueous solution on two types of weakly basic polymeric sorbent, tertiary amine D301R and primary amine D392, was investigated over a wide pH range and at various salt (MgSO4) concentrations. RESULTS: Overloading adsorption of pyruvic acid on both weakly basic polymeric sorbents occurred, with the overloading of D392 being greater than that of D301R. The adsorption of pyruvic acid on both sorbents was greatly affected by the solution pH and the salt concentration in the aqueous phase. An overloading model was able to predict the experimental uptake data very well. CONCLUSION: Solution pH is one of the most important operating conditions, and both polymeric sorbents D392 and D301R can be used to recover pyruvic acid from dilute aqueous solution with high efficiency at a solution pH around 2. The uptake by D392 is greater than that by D301R owing to steric hindrance of the tertiary amine. Copyright © 2008 Society of Chemical Industry  相似文献   
25.
This article proposes a novel parallel, hardware-oriented deadlock detection algorithm for multiprocessor system-on-chips. The proposed algorithm takes full advantage of hardware parallelism in computation and maintains information needed by deadlock detection through classifying all resource allocation events and performing class specific operations, which together make the overall run-time complexity of the new method O(1). We implement the proposed algorithm in Verilog HDL and demonstrate in the simulation that each algorithm invocation takes at most four clock cycles in hardware.  相似文献   
26.
Hydrothermal Synthesis of Magnesium Aluminate Platelets   总被引:1,自引:0,他引:1  
Magnesium aluminate (MgAl2O4) platelets were first synthesized by hydrothermal treatment of γ-AlO(OH) in a magnesium nitrate aqueous solution at 400°C. The platelets are 100–200 nm in width and 25 nm in thickness. The influence of temperature, the anions of the magnesium salt, the amount of magnesium salt, and precursor pH on the formation of such structure was investigated. The experimental results indicated that the anions of the magnesium salt and precursor pH could have a significant influence on the growth of MgAl2O4. MgAl2O4 formation followed the in situ transformation mechanism, which was the reason why the MgAl2O4 crystallites had a platelet morphology.  相似文献   
27.
Abstract The whole DNA of soybean was implanted into four varieties of wheat of Zhongyu5, Huaiyin 9628, Wenyou 1, Jimai 5 respectively via ion-beam mediation. There were 5 plantsobtained whose protein content was higher than 18.5%, the highest one was 21.44%. There were 3plants obtained whose protein content was lower than 11.5%, the lowest one was 10.96%. We cansee that the whole DNA of soybean transformed into wheat via ion beam implantation can inducethe increase in wheat protein content dramatically. The result also shows that the transformationefficiency of different gene types of wheat receptor varies greatly that the implanting time has acertain effect on the efficiency of transformation.  相似文献   
28.
29.
本文主要完成了液态金属钠高温沸腾实验回路的应力分析与计算,确定了回路高温区连接管系的布置型式和支吊架系统,是该回路总体设计的重要组成部分。  相似文献   
30.
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