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   403467篇
  免费   19574篇
  国内免费   9732篇
电工技术   15695篇
技术理论   24篇
综合类   14240篇
化学工业   66436篇
金属工艺   20593篇
机械仪表   19563篇
建筑科学   21927篇
矿业工程   8370篇
能源动力   11051篇
轻工业   29706篇
水利工程   5264篇
石油天然气   19721篇
武器工业   1649篇
无线电   44625篇
一般工业技术   59949篇
冶金工业   45697篇
原子能技术   6516篇
自动化技术   41747篇
  2023年   4103篇
  2022年   7228篇
  2021年   10365篇
  2020年   7951篇
  2019年   7217篇
  2018年   8760篇
  2017年   9551篇
  2016年   8867篇
  2015年   10377篇
  2014年   13893篇
  2013年   20914篇
  2012年   18644篇
  2011年   21621篇
  2010年   18335篇
  2009年   18429篇
  2008年   18075篇
  2007年   17548篇
  2006年   17243篇
  2005年   15331篇
  2004年   11644篇
  2003年   10307篇
  2002年   9515篇
  2001年   8954篇
  2000年   9293篇
  1999年   10441篇
  1998年   15732篇
  1997年   11776篇
  1996年   9785篇
  1995年   7743篇
  1994年   6402篇
  1993年   5506篇
  1992年   4121篇
  1991年   3746篇
  1990年   3327篇
  1989年   3162篇
  1988年   2906篇
  1987年   2460篇
  1986年   2344篇
  1985年   2558篇
  1984年   2322篇
  1983年   2123篇
  1982年   2000篇
  1981年   2039篇
  1980年   1865篇
  1979年   1852篇
  1978年   1799篇
  1977年   2126篇
  1976年   2721篇
  1975年   1565篇
  1973年   1620篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
12.
本文通过径流还原计算和绘制降水径流深相关图的方法,对天然年径流系列的一致性进行了分析,并通过实例验证了该方法可使水文资料系列更具代表性。  相似文献   
13.
It was found that vanadyl porphyrin complexes synthesized from petroleum metal porphyrin concentrates stimulated epoxidation during the olefin oxygenation process. The yields of obtained oxiranes turned out to be 38–75%, depending on the olefin structure. An epoxidation mechanism that suggests the formation of a protonated dioxygen adduct as an intermediate during oxygenation of olefins in the presence of vanadyl porphyrin complexes was proposed. An analogy is drawn between the epoxide formation reaction upon the catalytic oxygenation of olefins and the Prilezhaev reaction.  相似文献   
14.
The Magnitogorsk Metallurgical Combine has conducted a study of the effect of technological factors on the hydrogen content of chromium-nickel-molybdenum steel after vacuum degassing. It was established that the most important factor is the hydrogen content of the steel before the degassing operation. The study also determined the effects of the circulation coefficient, the duration of the degassing operation, and the vacuum used in the treatment. __________ Translated from Metallurg, No. 7, pp. 68–69, July, 2006.  相似文献   
15.
Based on the current spin density functional theory, a theoretical model of three vertically aligned semiconductor quantum dots is proposed and numerically studied. This quantum dot molecule (QDM) model is treated with realistic hard-wall confinement potential and external magnetic field in three-dimensional setting. Using the effective-mass approximation with band nonparabolicity, the many-body Hamiltonian results in a cubic eigenvalue problem from a finite difference discretization. A self-consistent algorithm for solving the Schrödinger-Poisson system by using the Jacobi-Davidson method and GMRES is given to illustrate the Kohn-Sham orbitals and energies of six electrons in the molecule with some magnetic fields. It is shown that the six electrons residing in the central dot at zero magnetic field can be changed to such that each dot contains two electrons with some feasible magnetic field. The Förster-Dexter resonant energy transfer may therefore be generated by two individual QDMs. This may motivate a new paradigm of Fermionic qubits for quantum computing in solid-state systems.  相似文献   
16.
The pill-box and block RF windows for millimeter wave (MMW) tubes are presented. The pill-box window is suitable for broadband MMW tubes. And the block window can be used for high power tubes in short MMW. The equivalent circuits for two windows are given. To reach better match characteristics in wider operating bandwidth, the optimum design methods for pill-box and block window in MMW tubes are described in this paper. The testing results show that the theoretic computation is fast and useful accuracy. The design methods possess references value to designer for MMW tubes.  相似文献   
17.
Using Java-based tools in multimedia collaborative environments accessed over the Internet can increase an application's client base. Most operating systems support Java, and its "compile once-run everywhere" architecture is easy to maintain and update. The Java-based tools presented here let users share Internet resources, including resources originally designed for single use.  相似文献   
18.
At some point in their careers, clinicians who work or consult in forensic and correctional settings will almost certainly encounter individuals who exhibit psychopathic personality features. Because of the widespread use of this disorder to inform legal and clinical decision making, psychologists should be exceedingly familiar with the relevant research literature on this topic before venturing into these settings. This article reviews the empirical bases of several clinically relevant claims and assertions regarding psychopathy and concludes that many areas of research are decidedly more equivocal in their findings than is commonly perceived. Although there is much to be gained by assessing psychopathy in various contexts, clinicians need to be cautious about drawing overzealous and empirically questionable conclusions about an important disorder that also has great potential for abuse. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
19.
文章介绍了一种新型的短波跳频通信技术——差分跳频,分析了差分跳频技术区别于常规跳频技术的主要特点。针对按序列检测的信号接收方法,对差分跳频通信系统在AWGN信道下的性能进行了理论分析,同时做出相应的计算机仿真,证实了差分跳频通信技术和按序列检测方法的结合,使通信系统在AWGN信道下的性能得到了比较显著的提升。  相似文献   
20.
The application of barrier discharges at atmospheric pressure in air expands on the market of plasma technology, because it is an ecological and cost‐effective alternative to other processes of surface treatment. These plasmas usually consist of a multitude of spatially and temporally localized filaments, whose distribution should be as even as possible for homogeneous treatment. This holds especially for the plasma treatment of sensitive goods such as wool or other textiles. In equipment for continuous pass of material the barrier arrangements often consist of a system cylinder – cylinder or cylinder – plane, whereby the gap width changes locally. Space distribution and intensity of filaments has been investigated by means of short‐time photography and spatially resolved measurement of current distribution and energy distribution derived from it. The local dependency found can be explained by means of a capacitive equivalent circuit.  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