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   19091篇
  免费   1659篇
  国内免费   854篇
电工技术   1072篇
技术理论   3篇
综合类   1272篇
化学工业   3340篇
金属工艺   997篇
机械仪表   1053篇
建筑科学   1587篇
矿业工程   559篇
能源动力   540篇
轻工业   1142篇
水利工程   349篇
石油天然气   1263篇
武器工业   148篇
无线电   2223篇
一般工业技术   2652篇
冶金工业   841篇
原子能技术   215篇
自动化技术   2348篇
  2024年   81篇
  2023年   327篇
  2022年   550篇
  2021年   844篇
  2020年   572篇
  2019年   537篇
  2018年   575篇
  2017年   590篇
  2016年   532篇
  2015年   718篇
  2014年   882篇
  2013年   1003篇
  2012年   1167篇
  2011年   1249篇
  2010年   1115篇
  2009年   1076篇
  2008年   1024篇
  2007年   990篇
  2006年   1015篇
  2005年   890篇
  2004年   603篇
  2003年   585篇
  2002年   502篇
  2001年   436篇
  2000年   481篇
  1999年   512篇
  1998年   454篇
  1997年   421篇
  1996年   383篇
  1995年   346篇
  1994年   252篇
  1993年   207篇
  1992年   155篇
  1991年   93篇
  1990年   109篇
  1989年   117篇
  1988年   70篇
  1987年   31篇
  1986年   29篇
  1985年   22篇
  1984年   14篇
  1983年   9篇
  1982年   15篇
  1981年   8篇
  1980年   8篇
  1979年   1篇
  1978年   1篇
  1976年   2篇
  1959年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
This paper presents a new route about producing carbon black,by wich the natural gas cracking is carried out in the absence of oxygen thanks to an electric energy supply externally given by a plasma jet.The carbon black produced by this process has a narrow size distribution and a small average diameter of 38nm as well as a highly branched aggregate.The higher DBP value of 1.40ml/g shows it should be a high structure carbon black.The FTIR spectra shows that there are lots of aromatic c-c bonds and a large amount of nitrogen-coutaining functional groups on the carbon blacks surface,such as-NH,-CN as we3ll as -CH,-OH,-COOH groups.  相似文献   
32.
元数学对计算机科学的启示   总被引:2,自引:0,他引:2  
文章提出了元数学对计算机科学的几点启示,这几个方面分别是传统程序设计的概念、机制、要素,数据库技术中的数据模型和函数依赖,面向对象分析和设计方法。文中一方面分析了元数学所提供的理论基础,另一方面说明了在应用方面是如何体现这些理论基础的,并提出了在计算机技术领域中应从数学基础问题、数理逻辑等的相关理论着手寻找突破的思想。  相似文献   
33.
A new alternating-direction implicit (ADI) scheme for solving three-dimensional parabolic differential equations has been developed based on the idea of regularized difference scheme. It is unconditionally stable and second-order accurate. Further, it overcomes the drawback of the Douglas scheme and is to be very well to simulate fast transient phenomena and to efficiently capture steady state solutions of parabolic differential equations. Numerical example is illustrated.  相似文献   
34.
非正弦不对称三相三线电路负载侧相电压的定义与测量   总被引:1,自引:0,他引:1  
对非正弦不对称三相三线电路,如何恰当地定义负载侧的相电压并能方便地测量一直未有明确的统一认识。本文从研究三相三线电路中相电压与线电压的关系着手,根据外部等效的思想。来定义三相三线电路负载侧的相电压。按此定义的相电压恒满足u,+“b+“c=0,并可方便地通过三相电压互感器或直接依据负载侧的线电压来唯一确定负载侧的相电压。  相似文献   
35.
论述触变泥浆润滑套在沉井工程中的应用及主要参数。  相似文献   
36.
给出了一种新的LF半准开集定义,采用新的LF半准开集定义,较详细地研究了LF半准开集及半准连续函数的一些重要性质。  相似文献   
37.
A fuzzy constraint satisfaction approach for electronic shopping assistance   总被引:1,自引:0,他引:1  
The Internet and World Wide Web offer an additional channel for consumers to find, select, and buy products. However, unlike shopping in the traditional store, consumers have no direct contact with human clerks to get the required information in the electronic store. The objective of this paper is to propose a fuzzy constraint satisfaction approach to help buyers find fully satisfactory or replacement products in electronic shopping. For the buyer who can give precise product requirements, the proposed approach can generate product-ranking lists based on the satisfaction degrees of each product to the given requirements. For the buyer who may not input accurate requirements, a similarity analysis approach is proposed to assess buyer requirements automatically during his browsing process. The proposed approach could help buyers find the preferred products on the top of the ranking list without further searching the remaining pages. The experimental results show the applicability of the proposed approach for electronic shopping assistance.  相似文献   
38.
To study the new bone formation in the bone defect area after implantation, the tetracycline tracing method was used. The results show that new bone formed in 1 month, and the formation rate of new bone was very high (8. 164 μm/day), considerably faster than that of control groups (3.219 μm/day). The new bone grew up quickly and β_TCP particles were surrounded by double fluorescence bands which became more obvious. The new bone formation rate was maximal at 2 months, and then gradually reduced. The rate was steady at 4 months, and then reduced to resembling as the normal physiologic metabolism of bone, which indicated the implanted materials were completely replaced by bone. Calcium phosphate materials had the ability of osteoconduction.  相似文献   
39.
戴术辉 《铜业工程》2004,(3):41-42,13
由于供电线路故障、浪涌、断线或其它干扰都可能导致电力系统服务中断 ,而FCM2 0 0电力监控仪可在线进行谐波分量测量 ,具备数字波形高速采集功能 ,它的波形分析工具可诊断谐波等故障根源 ,并且有助于确定必要的保护措施。  相似文献   
40.
Polypropylene (PP)'s low impact strength limits its usages. Adding some a rare earth polymer can enhance PP's tensile strength and impact strength. Acrylic lanthanum was prepared by the reaction between lanthanum oxide and acrylic acid. The IR spectrum prove that and optimum reacting conditions are that the bulk ratio of La(AA) 3 and MMA is not less than one and temperature is about 80 ℃. Lanthanum containing Polymer were added into PP. When percent of addition only was 3%, strength were enhanced 10% , and impact strength 40%. SEM shows the compatibility of rare earth polymer and PP; lanthanum containing polymer can form physical crosslinking between PP's molecules, then every particle's surface connect with several PP molecules and the PP mechanical property were enhanced.  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