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   336145篇
  免费   35764篇
  国内免费   14506篇
电工技术   19603篇
技术理论   16篇
综合类   19631篇
化学工业   63634篇
金属工艺   17226篇
机械仪表   19508篇
建筑科学   26050篇
矿业工程   8265篇
能源动力   9675篇
轻工业   26009篇
水利工程   6046篇
石油天然气   15576篇
武器工业   2610篇
无线电   42458篇
一般工业技术   45496篇
冶金工业   15279篇
原子能技术   3583篇
自动化技术   45750篇
  2024年   1294篇
  2023年   4430篇
  2022年   8343篇
  2021年   11703篇
  2020年   9665篇
  2019年   9789篇
  2018年   10391篇
  2017年   11970篇
  2016年   11710篇
  2015年   14705篇
  2014年   17993篇
  2013年   22454篇
  2012年   21617篇
  2011年   23733篇
  2010年   21345篇
  2009年   20776篇
  2008年   19920篇
  2007年   19182篇
  2006年   18859篇
  2005年   15980篇
  2004年   11678篇
  2003年   10384篇
  2002年   9984篇
  2001年   8818篇
  2000年   8049篇
  1999年   7498篇
  1998年   6132篇
  1997年   5062篇
  1996年   4508篇
  1995年   3782篇
  1994年   3136篇
  1993年   2453篇
  1992年   1894篇
  1991年   1435篇
  1990年   1130篇
  1989年   981篇
  1988年   745篇
  1987年   552篇
  1986年   451篇
  1985年   354篇
  1984年   231篇
  1983年   225篇
  1982年   181篇
  1981年   164篇
  1980年   145篇
  1979年   104篇
  1978年   67篇
  1977年   72篇
  1976年   80篇
  1975年   39篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
本文实验研究了BHP的浓度对产生O2(1△)的影响。实验结果表明:当BHP浓度大于3.5M时,Cl2利用率以及O2(1△)的产率将不依赖于BHP浓度的变化而变化,同时,实验结果表明,使用低浓度的BHP对COIL的操作是可行的。  相似文献   
102.
It has been found that the subthreshold currents of fully depleted silicon-on-insulator (SOI) MOSFETs show a transient behavior under certain front-gate and back-gate voltage conditions. The cause of this anomaly is explained, and applications for the phenomenon are pointed out. Particularly, a simple way to measure the silicon film thickness is suggested  相似文献   
103.
针对双组分等温平行反应体系,分析讨论了以提高催化剂活性和选择性为目标时催化剂活性组分的最优分布形式(为δ-函数分布),并给出了确定这种反应体系的催化剂的最佳活性层位置的计算方法。结果表明:以提高选择性为目标的最佳活性层位置比以提高活性为目标的要更靠近催化剂核心,实用的最优位置应介于二者之间。最后,本文还研究了反应动力学级数、本性选择性以及内扩散模数(Thiele 模数)等因素对最佳活性层位置的影响。  相似文献   
104.
105.
InGaAs/GaAs(100) multiple-quantum-well-based inverted cavity asymmetric Fabry-Perot modulators are vertically integrated with GaAs/AlGaAs heterojunction phototransistors to yield all-optical photonic switches. The photonic switches using `normally on' modulator pixels exhibit an output on-off ratio of 12:1 with internal optical gain of 4 dB. The photonic switches using `normally off' modulator pixels yield similar contrast and gain, but exhibit intrinsic bistable behavior. The inverted cavity modulators employed permit utilizing the transparency of the GaAs substrate at the operating wavelength and offer advantages for fabricating large arrays for optical signal processing  相似文献   
106.
The buried-type p-channel LDD MOSFETs biased at high positive gate voltage exhibit novel characteristics: (1) the ratio of the drain to gate currents is about 1×10-3 to 5×10-3; and (2) the gate and drain currents both are functions of only the gate voltage minus the n-well bias. Such characteristics are addressed based on the formation of the surface n + inversion layer due to the punchthrough of the buried channel to the underlying shallow p-n junction. The measured gate current is due to the Fowler-Nordheim tunneling of electrons from this inversion layer surface and the holes generated within the high-field oxide constitute the drain current. The n+ inversion layer surface potential is found to be equal to the n-well bias plus 0.55 V. As a result, both the oxide field and the gate and drain currents are independent of drain voltage  相似文献   
107.
Micro‐porous syntactic foams were produced by means of integration of glass bubbles into aluminium and zinc matrices. Preforms of glass bubbles were pressure infiltrated with the alloys AlSi9Cu9 ans ZnAl4Cu using squeeze casting. The preforms were sintered thermically without the use of bonding agents. Using the combination of different sintering steps syntactic foams with locally different densities could be produced. The mechanical properties of the foams were tested indicating a high compression strength of the foams and a very good compression energy absorption. Furthermore, corrosion behaviour and behaviour at higher temperatures were investigated.  相似文献   
108.
We define the very rich language of composed conditionals on a three‐valued logic and use this language as the communication tool between man and machine. Communication takes place for three reasons: knowledge acquisition, query, and response. Learning, thinking, and answering questions are of a pure information theoretical nature. The pivot of this knowledge processing concept is the amount of information (bit) we receive if a conditional becomes true. We follow an axiomatic approach to information theory rather than the classical probabilistic approach of Shannon; information comes first, and then comes probability. In the light of this philosophy, query and response experience new interpretations. Both, acquisition and response are realized by maximizing entropy and minimizing relative entropy, respectively. The iterative solution of these mathematical optimization problems gives new insights into the adaptation of prior knowledge to new information. Our expert system shell SPIRIT supports this kind of knowledge processing, which will be established by suitable examples. © 2003 Wiley Periodicals, Inc.  相似文献   
109.
110.
The temperature dependence characteristics of hydrogenated amorphous silicon thin-film transistors were investigated. The results indicate that as the temperature was increased, the threshold voltage and the field-effect mobility were first increased, and then decreased, which may be controlled by different mechanisms at low and high temperatures. In addition, if the temperature was higher than 420 K, the Fermi level was promoted to the degenerate-like states, the current channel always existed due to the temperature effect, and the threshold voltage became negative.  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