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   63603篇
  免费   8457篇
  国内免费   2384篇
电工技术   2292篇
综合类   2805篇
化学工业   22968篇
金属工艺   3445篇
机械仪表   1874篇
建筑科学   4569篇
矿业工程   1880篇
能源动力   1679篇
轻工业   8224篇
水利工程   1019篇
石油天然气   2268篇
武器工业   329篇
无线电   4598篇
一般工业技术   6954篇
冶金工业   3307篇
原子能技术   807篇
自动化技术   5426篇
  2024年   276篇
  2023年   1265篇
  2022年   3869篇
  2021年   4164篇
  2020年   2112篇
  2019年   2177篇
  2018年   2351篇
  2017年   2977篇
  2016年   4094篇
  2015年   4484篇
  2014年   4755篇
  2013年   5072篇
  2012年   3760篇
  2011年   2978篇
  2010年   2494篇
  2009年   2554篇
  2008年   2308篇
  2007年   3527篇
  2006年   3732篇
  2005年   3075篇
  2004年   2103篇
  2003年   2050篇
  2002年   1521篇
  2001年   1051篇
  2000年   978篇
  1999年   639篇
  1998年   439篇
  1997年   411篇
  1996年   385篇
  1995年   290篇
  1994年   332篇
  1993年   244篇
  1992年   220篇
  1991年   228篇
  1990年   209篇
  1989年   162篇
  1988年   99篇
  1987年   100篇
  1986年   83篇
  1985年   117篇
  1984年   118篇
  1983年   74篇
  1982年   74篇
  1981年   45篇
  1980年   56篇
  1979年   26篇
  1966年   25篇
  1964年   34篇
  1962年   64篇
  1955年   22篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
造纸与化工混合污水处理生化动力学研究   总被引:1,自引:0,他引:1  
采用造纸厂中段污水、化肥厂含氨氮污水、化工厂含酚污水、农药厂有机磷污水按不同比例混合,研究在微生物作用下生物降解过程,揭示其生化动力学规律。研究结果表明,混合污水生化动力学系数为衰减系数K_d=0.035d~(-1),产率系数Y=0.864mg(VSS)/mg(BOD_5),底物最大比降解速率为q_(max)=0.201mg(BOD_5)/mg(VSS)d,半速率系数为K_s=48.9mg(BOD_5)/L。实验结果所得的生化动力学系数,为区域性污水集中处理提供理论参考依据。  相似文献   
992.
In this paper, Zr, Cr and V were selected as the partial substitution elements for Ti to form Mg35Ti5M5Ni55 quaternary alloys prepared by means of mechanical alloying on the basis of the ternary Mg35Ti10Ni55 electrode alloy previously studied by the authors. It is found that all the three quaternary alloys possess an amorphous main phase and exhibit improved cycling stability than the original ternary Mg35Ti10Ni55. The Zr-substituted alloy has also a higher discharge capacity. X-ray photoelectron spectroscopy (XPS) surface analysis reveals that on the surface of each alloy a multi-component oxide composite film is formed, which is more compact and corrosion resistant than the Mg(OH)2 film and the (TiO2)x(NiO)y(Mg(OH)2)z composite films reported previously. Auger electron spectroscopy (AES) analysis shows that the substituting elements tend to reduce the thickness of the passivation films. The thickness of composite oxide film on the alloys is in the following order: Mg35Ti10Ni55>Mg35Ti5V5Ni55>Mg35Ti5Zr5Ni55>Mg35Ti5Cr5Ni55. The result agrees well with that of the polarization resistances (RP) values obtained from the electrochemical impedance spectroscopy (EIS) Nyquist diagrams. It demonstrates that the thicker the passivation film is, the higher the RP is and the more difficultly the charge transfer reaction proceeds. Anodic polarization curves indicate that the addition of Cr and Zr decreases effectively the corrosion current. However, the corrosion of the electrode alloys in the electrolyte is still high and proceeds constantly as the corrosion current remains almost constant during further cycles.  相似文献   
993.
The hot compression tests using Gleeble 1500 were performed by varying the true strain up to 1.6 (80% reduction) in Nbfree and Nb-microalloyed steels. The effect of Nb addition on the transformation kinetics during deformation of undercooled austenite was investigated. It was found that as compared with Nb-free steel, the transformation incubation period of Nb-bearing steel was prolonged and the transformation kinetics curves parallelly moved to higher strain because of the solute Nb drag effect. Studies on kinetics also showed that the deformation-enhanced ferrite transformation (DEFT) of the two steels were composed of three stages, which can be expressed by the J-M-A equations individually. However, the parameter n related to the mode of nucleation and growth is somewhat different in the first and second stages of the two steels, and the same in the third stage for both the steels corresponding to the nucleation Of retained austenite.  相似文献   
994.
随着生活水平的提高,使用高效低毒消毒剂已成为当务之急.ClO2是优良的氧化型消毒剂,ClO2对水中有机物的氧化降解以含氧基团的小分子化合物为主,即最终以无毒害作用的产物为主.因此ClO2在水处理中的应用越来越受到重视.但作为替代液氯的消毒剂,ClO2同样会产生副产物,其安全性同样要予以重视.  相似文献   
995.
针对零件结构中几何元素与附着于几何元素之上的设计意图的统一表示问题,提出了基于联结语义的概念结构建模方法.该方法在零件概念结构抽象和分解的基础上,以更符合设计者表达习惯的语义形式简洁地表示零件结构间的约束关系.分析了在结构设计过程中的联结语义及其蕴涵的约束信息,建立了联结语义的约束规则集描述方法.采用联结语义关联图给出了面向概念设计的零件结构模型,实现了结构联结约束信息的抽象表达.实例研究结果表明,该建模方法使设计者可以更直观、自然地在高层次的语义层表达产品设计信息,实现工程语义的形式化表述.  相似文献   
996.
高技术产业发展影响因素的实证研究--投入、机制与环境   总被引:1,自引:1,他引:1  
采用回归分析和相关分析方法,利用跨国数据对投入因素、机制因素以及外部环境等因素影响一国高技术产业发展水平的机理进行了实证研究,结果表明,提高高技术产业的发展水平需要保证R&D的投入规模与合理处理R&D的投入结构、加大科技人力资源的投入,需要适宜的金融体系尤其是风险投资的发展与支持,同时健康的产业发展机制、人们积极的创业精神、适宜的社会经济、文化以及教育背景等都是促进高技术产业健康发展的保证。  相似文献   
997.
研制了一种以硅灰石、锂辉石为主要助熔剂,烧结温度在1150℃的低温日用光泽透明釉,性能达到了国家标准。文章通过对其烧成过程和显微结构观测,探讨了其烧成机理,以及助熔剂在成釉过程中的作用。  相似文献   
998.
The failure pattern of repairable mechanical equipment subject to deterioration phenomena sometimes shows a finite bound for the increasing failure intensity. A non-homogeneous Poisson process with bounded increasing failure intensity is then illustrated and its characteristics are discussed. A Bayesian procedure, based on prior information on model-free quantities, is developed in order to allow technical information on the failure process to be incorporated into the inferential procedure and to improve the inference accuracy. Posterior estimation of the model-free quantities and of other quantities of interest (such as the optimal replacement interval) is provided, as well as prediction on the waiting time to the next failure and on the number of failures in a future time interval is given. Finally, numerical examples are given to illustrate the proposed inferential procedure.  相似文献   
999.
Peter   《World Patent Information》2006,28(4):296-304
The nature, definition, typical services, utility and future developments in Open Patent Services (OPS) are described. This is with particular reference to the European Patent Office (EPO), and German Patent and Trademark Office (GPTO) systems. The impact of OPS on both information providers and users is discussed.  相似文献   
1000.
One of the most important objectives in the surface engineering of light-weight alloys is to enhance their fatigue properties, allowing both increased performance and an extended service life. This can be achieved by forming a hard surface layer while incorporating a favourable stress state. Single surface treatments, for example, Plasma Electrolytic Oxidation (PEO), are not always capable of creating optimal combinations of these characteristics, whereas greater durability can be achieved by applying mechanical pre-treatments prior to the coating. In this work, a combination of shot-peening pre-treatment with plasma electrolytic oxidation coating is studied as a means to improve the fatigue performance of 2024 T351 Al alloy. The shot-peening was carried out in a compressed air configuration using S110 gauge shot at 200% coverage with an intensity of 20 AlmenC. PEO coatings of 30 μm thickness were produced using pulsed bipolar current technology. Fatigue properties were evaluated by a four-point bending technique at a stress ratio of 0.1. Hardness, residual stress and microstructure of the surface layers were studied by Knoop microhardness tests, fluorescence spectroscopy and SEM analyses, respectively. The effect of the combined shot-peening and PEO treatment is an increased fatigue limit and elevated microhardness when compared to aluminium treated only with PEO.  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