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   108009篇
  免费   9176篇
  国内免费   4890篇
电工技术   6807篇
技术理论   2篇
综合类   6945篇
化学工业   16528篇
金属工艺   6100篇
机械仪表   6361篇
建筑科学   8127篇
矿业工程   2467篇
能源动力   3055篇
轻工业   8490篇
水利工程   2144篇
石油天然气   4999篇
武器工业   834篇
无线电   13998篇
一般工业技术   13606篇
冶金工业   5474篇
原子能技术   1162篇
自动化技术   14976篇
  2024年   474篇
  2023年   1691篇
  2022年   3108篇
  2021年   4309篇
  2020年   3083篇
  2019年   2572篇
  2018年   2843篇
  2017年   3395篇
  2016年   2926篇
  2015年   4073篇
  2014年   5338篇
  2013年   6668篇
  2012年   7144篇
  2011年   7891篇
  2010年   6911篇
  2009年   6663篇
  2008年   6538篇
  2007年   6276篇
  2006年   6158篇
  2005年   5153篇
  2004年   3448篇
  2003年   2881篇
  2002年   2884篇
  2001年   2426篇
  2000年   2302篇
  1999年   2339篇
  1998年   2170篇
  1997年   1876篇
  1996年   1673篇
  1995年   1413篇
  1994年   1101篇
  1993年   867篇
  1992年   694篇
  1991年   525篇
  1990年   442篇
  1989年   349篇
  1988年   294篇
  1987年   203篇
  1986年   166篇
  1985年   149篇
  1984年   109篇
  1983年   83篇
  1982年   76篇
  1981年   65篇
  1980年   53篇
  1979年   35篇
  1978年   32篇
  1977年   32篇
  1976年   54篇
  1973年   21篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
In this study, the effect and side-effect of epidural injection with lappaconitine compound for post-operative analgesia was observed. One hundred and twenty patients were randomly divided into 4 groups. Lappaconitine compound (LB) consisted of 12 mg of lappaconitine and 22.5 mg of bupivacaine, was given to group A (the group of observation), and lappaconitine 12 mg, bupivacaine 22.5 mg and morphine 2 mg to group B, C and D respectively for control. All were given by epidural injection with single blind method during post-operative pain of incision operation. Result showed that the initiating of analgesia was quicker in group A and C than that in group B and D, and the efficacy was group D > A > C > B. There was significant difference between group A and B in the above two parameters, P < 0.01 and P < 0.05. The analgisia maintenence time of single injection was D > A > B > C, that of group D was significantly longer than that of group A (P < 0.01). It indicated that the epidural injection with LB was more rapid and potent than that with lappaconitine alone in post-operative analgesia, and the former had no side-effect, it was safer than morphine.  相似文献   
22.
本文概述了离子注入过程中污染产生的原因和防止污染的措施,特别强调了对微粒污染和金属污染的防护以满足ULSI加工对离子注入的要求。  相似文献   
23.
24.
An authenticated multiple-key agreement protocol is proposed. The protocol is not only secure against the unknown-key attack but also more efficient than other protocols.  相似文献   
25.
Using AuGeNiCr multilayered metals as the wafer bonding medium, long-wavelength GaInAsP/InP vertical cavity surface emitting lasers employing Al-oxide/Si as the upper and lower distributed Bragg reflectors were fabricated on Si substrate with the bonding interface formed outside the vertical cavity surface emitting laser cavity. Laser emission at 1.545 μm was measured under pulsed operations near room temperature. The low-temperature metallic bonding process demonstrates a great potential in device fabrication  相似文献   
26.
Coplanar waveguide-fed uniplanar bow-tie antenna   总被引:3,自引:0,他引:3  
The design of coplanar waveguide (CPW)-fed bow-tie antenna for the 2.4-GHz ISM band is described. A coplanar waveguide-to-coplanar strips (CPW-to-CPS) balun is used to obtain the balanced feed line for the printed bow-tie. An analysis method based on the mixed potential integral equation method is used to characterize the input characteristics of the bow-tie antenna. The numerical results obtained are in good agreement with the experimental data. Through experiments with bow-tie antennas of various extended angles, the bow-tie antenna with a 90° extended angle exhibits the widest bandwidth in the desired frequency band which has a bandwidth of 17% for a VSWR <1.5:1  相似文献   
27.
Ion-ripple laser, which consists of a relativistic electron beam obliquely propagating through an ion-ripple in a plasma, is investigated by nonlinear numerical simulation. The influence of the component of the ion-ripple field parallel to the beam direction on beam-wave interaction is analyzed. The results show that the longitudinal component of the ion-ripple field has a considerable influence on ion-ripple laser. The operating parameters are also optimized.  相似文献   
28.
Color image retrieval based on hidden Markov models   总被引:1,自引:0,他引:1  
In this correspondence, a new approach to retrieving images from a color image database is proposed. Each image in the database is represented by a two-dimensional pseudo-hidden Markov model (2-D PHMM), which characterizes the chromatic and spatial information about the image. In addition, a flexible pictorial querying method is used, by which users can paint the rough content of the desired images in a query picture. Image matching is achieved by comparing the query picture with each 2-D PHMM in the database. Experimental results show that the proposed approach is indeed effective.  相似文献   
29.
Identifies the basic technological components of multimedia communications. Among these technologies, multimedia processing and transmission already benefit heavily from VLSI advances. in fact, these two technologies could not have matured without special-purpose VLSI chips. We have examined basic processing required in these technologies and some VLSI architectures. The focus has been on standard-compliant VLSI chips, because the eventual goal of communications is to allow everyone to reach others without constraints. There are still a number of evolving standards, which means that we might witness yet another wave of VLSI chips for multimedia communications  相似文献   
30.
本文用计算机数字模拟方法研究了电活性分子多层Z型L-B膜修饰电极的循环伏安行为。计算了电极与修饰L-B膜分子第一层之间的电荷转移速度常数K_o,L-B膜分子层间的电荷转移速度常数k_i;对峰电位差△E_p及阳极峰面积Q的影响,以及在不同条件下各层分子的氧化态分数随扫描时间的变化。为研究和设计电活性分子修饰电极的实际体系提供了大量数据和信息。  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