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   3276篇
  免费   97篇
  国内免费   4篇
电工技术   44篇
综合类   12篇
化学工业   658篇
金属工艺   98篇
机械仪表   98篇
建筑科学   70篇
能源动力   130篇
轻工业   199篇
水利工程   8篇
石油天然气   4篇
武器工业   1篇
无线电   579篇
一般工业技术   588篇
冶金工业   371篇
原子能技术   21篇
自动化技术   496篇
  2023年   19篇
  2022年   59篇
  2021年   63篇
  2020年   28篇
  2019年   32篇
  2018年   44篇
  2017年   51篇
  2016年   67篇
  2015年   67篇
  2014年   94篇
  2013年   244篇
  2012年   149篇
  2011年   193篇
  2010年   189篇
  2009年   215篇
  2008年   180篇
  2007年   183篇
  2006年   134篇
  2005年   101篇
  2004年   106篇
  2003年   88篇
  2002年   90篇
  2001年   62篇
  2000年   65篇
  1999年   61篇
  1998年   162篇
  1997年   96篇
  1996年   80篇
  1995年   51篇
  1994年   48篇
  1993年   44篇
  1992年   36篇
  1991年   41篇
  1990年   33篇
  1989年   21篇
  1988年   15篇
  1987年   13篇
  1986年   14篇
  1985年   15篇
  1984年   20篇
  1983年   7篇
  1982年   13篇
  1981年   14篇
  1980年   9篇
  1979年   8篇
  1978年   6篇
  1977年   10篇
  1976年   8篇
  1973年   5篇
  1971年   5篇
排序方式: 共有3377条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
Hsiehchen  David  Espinoza  Magdalena  Hsieh  Antony 《Scientometrics》2018,117(1):391-407
Scientometrics - The expanding presence of multinational research teams highlights the importance of characterizing the outcomes of international collaboration. Herein, we characterize the...  相似文献   
5.
A novel circuit topology for low-phase-noise voltage controlled oscillators (VCOs) is presented in this letter. By employing a PMOS cross-coupled pair with a capacitive feedback, superior circuit performance can be achieved especially at higher frequencies. Based on the proposed architecture, a prototype VCO implemented in a 0.18-/spl mu/m CMOS process is demonstrated for K-band applications. From the measurement results, the VCO exhibits a 510-MHz frequency tuning range at 20GHz. The output power and the phase noise at 1-MHz offset are -3dBm and -111dBc/Hz, respectively. The fabricated circuit consumes a dc power of 32mW from a 1.8-V supply voltage.  相似文献   
6.
Electronic components are constantly under stress due to factors such as signal density, temperature, humidity, and high current and voltage. Relatively little research has emphasized stress-level prediction under voltage stress. The purpose of this paper was to develop an electronic thermal profile model for stress-level prediction utilizing neural network (NN) and statistical approaches, such as multivariate regression models. Electronic components were removed from boards, subjected to different levels of stress, then replaced. An infrared camera was then used to capture information about component temperature changes over time under normal operating and stress conditions. Statistical analysis of the captured images suggests a strong correlation between thermal profiles and voltage stress levels. Artificial neural network (ANN) and statistical approaches were used to model temperature change profiles for components that had been stressed at different levels, and their predictive ability was compared. Separate data sets were used for model development and model verification. ANN prediction rates were around 70%, compared to 30% for the statistical approach. Experiments were also conducted to evaluate the robustness of the ANN model to the presence of noise in the data. Results suggested that the ANN model was able to accommodate the presence of noise. Various backpropagation (BP) learning algorithms were also evaluated and yielded similar average error rates. A 3-2-1 ANN topology performed better than 3-3-1 or 3-2-2-1 topologies, perhaps because the 3-2-1 topology has a higher data sample to nodes ratio than the other topologies.  相似文献   
7.
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   
8.
Highly efficient orange and green emission from single‐layered solid‐state light‐emitting electrochemical cells based on cationic transition‐metal complexes [Ir(ppy)2sb]PF6 and [Ir(dFppy)2sb]PF6 (where ppy is 2‐phenylpyridine, dFppy is 2‐(2,4‐difluorophenyl)pyridine, and sb is 4,5‐diaza‐9,9′‐spirobifluorene) is reported. Photoluminescence measurements show highly retained quantum yields for [Ir(ppy)2sb]PF6 and [Ir(dFppy)2 sb]PF6 in neat films (compared with quantum yields of these complexes dispersed in m‐bis(N‐carbazolyl)benzene films). The spiroconfigured sb ligands effectively enhance the steric hindrance of the complexes and reduce the self‐quenching effect. The devices that use single‐layered neat films of [Ir(ppy)2sb]PF6 and [Ir(dFppy)2sb]PF6 achieve high peak external quantum efficiencies and power efficiencies of 7.1 % and 22.6 lm W–1) at 2.5 V, and 7.1 % and 26.2 lm W–1 at 2.8 V, respectively. These efficiencies are among the highest reported for solid‐state light‐emitting electrochemical cells, and indicate that cationic transition‐metal complexes containing ligands with good steric hindrance are excellent candidates for highly efficient solid‐state electrochemical cells.  相似文献   
9.
10.
This paper presents a particle penetration model predicting particle penetration coefficient (Pp) through a narrow crack of arbitrary incline angles (θ). The objective was to simulate Pp for outdoor-to-indoor particle penetration for residential infiltration conditions. This model assumes laminar infiltration flow and considers particle deposition from both gravitational sedimentation and Brownian diffusion. For micron-sized particles, modeling results indicate that gravitational sedimentation is the major deposition mechanism. Pp increases monotonically with ∣θ∣ because effective particle sedimentation velocity (vs?cos?θ) decreases monotonically with ∣θ∣. For submicron-sized particles (0.1?μm), Brownian diffusion is the major particle deposition mechanism. Because Brownian diffusion is a nondirectional deposition mechanism, crack inclination did not affect Pp. This study applied this model to estimate Pp for L-shaped cracks, and validated modeling results with experiments. Experimental results indicated that inertial impaction and crack entrance cutoff effects were not significant particle deposition mechanisms for the test micron-sized particles. Gravitational sedimentation was the major deposition mechanism. An L-shaped crack can be simulated as the combination of horizontal and vertical sections. This model agreed reasonably with experimental results.  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