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   189005篇
  免费   8372篇
  国内免费   3240篇
电工技术   5078篇
技术理论   4篇
综合类   5955篇
化学工业   29618篇
金属工艺   9658篇
机械仪表   9233篇
建筑科学   7492篇
矿业工程   2344篇
能源动力   4801篇
轻工业   11105篇
水利工程   2649篇
石油天然气   3369篇
武器工业   554篇
无线电   24671篇
一般工业技术   32998篇
冶金工业   10803篇
原子能技术   1646篇
自动化技术   38639篇
  2024年   312篇
  2023年   1464篇
  2022年   2500篇
  2021年   3686篇
  2020年   2736篇
  2019年   2513篇
  2018年   16873篇
  2017年   15943篇
  2016年   12824篇
  2015年   4125篇
  2014年   5051篇
  2013年   6909篇
  2012年   9909篇
  2011年   16682篇
  2010年   14205篇
  2009年   11715篇
  2008年   12451篇
  2007年   12841篇
  2006年   5134篇
  2005年   5407篇
  2004年   4656篇
  2003年   4400篇
  2002年   3835篇
  2001年   2847篇
  2000年   2544篇
  1999年   2367篇
  1998年   3011篇
  1997年   2068篇
  1996年   1826篇
  1995年   1481篇
  1994年   1101篇
  1993年   997篇
  1992年   742篇
  1991年   683篇
  1990年   551篇
  1989年   484篇
  1988年   427篇
  1987年   321篇
  1986年   310篇
  1985年   255篇
  1984年   221篇
  1983年   166篇
  1982年   164篇
  1981年   137篇
  1980年   132篇
  1979年   110篇
  1978年   96篇
  1977年   127篇
  1976年   160篇
  1975年   85篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
93.
The effects of gallia additions on the sintering behavior of gadolinia-doped ceria were systematically investigated from the following aspects: the variation in sintered density, the variation in grain size, and the existing forms of Ga2O3 in CeO2.Sintered density increased with increasing Ga2O3 content up to 5 mol.% and then it decreased with further addition of Ga2O3. Grain size also increased with increasing Ga2O3 content up to 5 mol.% and then decreased with further addition of Ga2O3. Decrease in grain size was caused by a pinning effect of Ga2O3 precipitation at grain boundaries. Lattice constant decreased with increasing Ga2O3 content up to 5 mol.%. This decrease will be due to the substitution of smaller Ga3+ ions for Ce4+ ions in the CeO2 structure. According to the results obtained from scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses, the solubility limit of Ga2O3 in Ce0.8Gd0.2O1.9 ceramics can be estimated to be nearly 5 mol.%. The addition of Ga2O3 up to the solubility limit was found to promote the sintering properties of Gd2O3-doped CeO2.  相似文献   
94.
We experimentally demonstrated the great advantages of a high dielectric constant thin film electromagnetic bandgap (EBG) power distribution network (PDN) for the suppression of power/ground noises and radiated emissions in high-performance multilayer digital printed circuit boards (PCBs). Five-layer test PCBs were fabricated and their scattering parameters measured. The power plane noise and radiated emissions were measured, investigated and related to the PDN impedance. This successfully demonstrated that the bandgap of the EBG was extended more than three times, covering a range of hundreds of MHz using a 1-cm /spl times/ 1-cm EBG cell, the SSN was reduced from 170 mV to 10 mV and the radiated emission was suppressed by 22 dB because of the high dielectric constant thin film EBG power/ground network.  相似文献   
95.
This paper looks at the concepts of entities, identities, identifiers and credentials, their definitions, and how they combine to authenticate an identity to an account, or function, within a service. Credentials can be divided into several different types on the basis of their use, origin and characteristics. In particular, types such as composite, dynamic and derived credentials will be considered, and their applicability within an identity management system. Each credential must be managed through its entire life cycle from initial registration, general use and suspension, to deletion. The notion of public (i.e. freely distributable) and private (i.e. known only to you) aspects of a credential is explored. The bindings, by trusted third parties, of identifiers and public credentials into permits and instruments of proof is explained along with the convenience, but greater exposure, of local information. Several scenarios are analysed in terms of how different types of credentials are employed during the authentication process.  相似文献   
96.
Yun  S. Park  S.Y. Lee  Y. Alsusa  E. Kang  C.G. 《Electronics letters》2005,41(13):752-754
A practical resource management method that can significantly reduce cochannel interference (CCI) and improve spectrum utilisation in FH-OFDMA packet-based cellular networks is presented. The proposed method seeks an effective combination of dynamic resource allocation with fractional coding and bit loading to respectively minimise CCI and maximise system throughput for a desired performance.  相似文献   
97.
We obtain a necessary and sufficient condition for a discrete-time nonlinear system to be locally state equivalent to the nonlinear observer form. The result looks similar to the continuous counterpart except for the fact that Ad-operation is utilized instead of ad-operation.  相似文献   
98.
Jeong  J. Kim  S. Choi  W. Noh  H. Lee  K. Seo  K.-S. Kwon  Y. 《Electronics letters》2005,41(18):1005-1006
A W-band divide-by-3 frequency divider with wide bandwidth and low power dissipation is presented using harmonic injection-locking technique. A cascode FET is employed for a self-oscillating second-harmonic mixer which is injection-locked by third-harmonic input to obtain the division order of three. The fabricated frequency divider using 0.1 /spl mu/m GaAs metamorphic HEMT technology shows superior performance such as large bandwidth of 6.1 GHz around 83.1 GHz (7.3%) under small DC power consumption of 12 mW.  相似文献   
99.
It is experimentally ascertained that light stimulates the negative magnetoresistance observed in a high electric field in silicon doped with boron and manganese. The optimum conditions (the electric field, temperature, illumination, and resistivity of the material) for observation of the largest magnitude of negative magnetoresistance in (Si:B):Mn are determined. The dependence of the negative magnetoresistance on the concentration of compensating impurity is established.  相似文献   
100.
Human facial gestures often exhibit such natural stochastic variations as how often the eyes blink, how often the eyebrows and the nose twitch, and how the head moves while speaking. The stochastic movements of facial features are key ingredients for generating convincing facial expressions. Although such small variations have been simulated using noise functions in many graphics applications, modulating noise functions to match natural variations induced from the affective states and the personality of characters is difficult and not intuitive. We present a technique for generating subtle expressive facial gestures (facial expressions and head motion) semi‐automatically from motion capture data. Our approach is based on Markov random fields that are simulated in two levels. In the lower level, the coordinated movements of facial features are captured, parameterized, and transferred to synthetic faces using basis shapes. The upper level represents independent stochastic behavior of facial features. The experimental results show that our system generates expressive facial gestures synchronized with input speech.  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