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   8970篇
  免费   418篇
  国内免费   82篇
电工技术   194篇
综合类   89篇
化学工业   1621篇
金属工艺   218篇
机械仪表   296篇
建筑科学   351篇
矿业工程   13篇
能源动力   279篇
轻工业   463篇
水利工程   38篇
石油天然气   44篇
武器工业   2篇
无线电   1760篇
一般工业技术   1595篇
冶金工业   1346篇
原子能技术   88篇
自动化技术   1073篇
  2023年   94篇
  2022年   136篇
  2021年   193篇
  2020年   147篇
  2019年   131篇
  2018年   193篇
  2017年   192篇
  2016年   192篇
  2015年   195篇
  2014年   290篇
  2013年   536篇
  2012年   445篇
  2011年   484篇
  2010年   385篇
  2009年   446篇
  2008年   450篇
  2007年   409篇
  2006年   374篇
  2005年   319篇
  2004年   301篇
  2003年   306篇
  2002年   255篇
  2001年   230篇
  2000年   212篇
  1999年   200篇
  1998年   518篇
  1997年   346篇
  1996年   230篇
  1995年   151篇
  1994年   131篇
  1993年   152篇
  1992年   82篇
  1991年   79篇
  1990年   71篇
  1989年   51篇
  1988年   55篇
  1987年   54篇
  1986年   61篇
  1985年   33篇
  1984年   32篇
  1983年   20篇
  1981年   41篇
  1980年   22篇
  1979年   21篇
  1978年   26篇
  1977年   42篇
  1976年   48篇
  1975年   12篇
  1974年   12篇
  1971年   12篇
排序方式: 共有9470条查询结果,搜索用时 15 毫秒
71.
The rapid increase in the number of patients with chronic diseases is an important public healthcare issue in many countries, which accelerates many studies on a healthcare system that can, whenever and wherever, extract and process patient data. A patient with a chronic disease conducts self‐management in an out‐of‐hospital environment, particularly in an at‐home environment, so it is important to provide integrated and personalized healthcare services for effective care. To help provide effective care for chronic disease patients, we propose a service flow and a new cloud‐based personalized healthcare system architecture supporting both at‐home and at‐hospital environments. The system considers the different characteristics of at‐hospital and at‐home environments, and it provides various chronic disease care services. A prototype implementation and a predicted cost model are provided to show the effectiveness of the system. The proposed personalized healthcare system can support cost‐effective disease care in an at‐hospital environment and personalized self‐management of chronic disease in an at‐home environment.  相似文献   
72.
A detection statistic for random-valued impulse noise.   总被引:1,自引:0,他引:1  
This paper proposes an image statistic for detecting random-valued impulse noise. By this statistic, we can identify most of the noisy pixels in the corrupted images. Combining it with an edge-preserving regularization, we obtain a powerful two-stage method for denoising random-valued impulse noise, even for noise levels as high as 60%. Simulation results show that our method is significantly better than a number of existing techniques in terms of image restoration and noise detection.  相似文献   
73.
The influence of the mobility reduction factor on the dominant third-harmonic distortion and effective transconductance in CMOS differential pair transconductors is examined. Analytical expressions are developed which are suitable for hand calculation and generate realistic estimates for distortion and transconductance. The results produced have been tested against SPICE simulations over a wide range of parameter values and show excellent agreement. The analysis highlights the importance of mobility degradation and reveals that the linearity of the source-coupled differential pair is actually improved as the mobility reduction factor increases. This surprising finding suggests that where 0.15, for example, acceptably low distortion levels (<60 dB for V i =1 V pp ) should be achievable with the basic long-tailed pair and that complex linearization schemes may be unnecessary.This work is supported by a grant of the Science and Engineering Research Council.  相似文献   
74.
王玉芝  傅恩生 《激光杂志》1992,13(5):243-245
本文用微机控制使反射镜扫描激光束,给出了CO_2激光的光强分布;用绕着光轴旋转的ZuSe布氏窗的反射和透射光强,给出了激光的偏振度。着重研究了内腔CO_2激光器的输出强度,增益,模式,能量分布,以及偏振度等光学参量间的相互关系。  相似文献   
75.
The use of semiconductor-film grafting for the hybrid integration of optoelectronic devices and its advantages in post-transfer fabrication are described. It is shown that grafted films are optically coupled to the substrate, making it possible to mix the semiconductor properties with some properties in the substrate, not commonly found in semiconductors, to yield new devices with no counterpart in other technologies. The semiconductor-film grafting, device fabrication, optical interaction between the semiconductor film and host substrate, and the integration of lasers with glass and LiNbO3 waveguides are discussed  相似文献   
76.
The performance of trellis-coded M-ary phase shift keying (MPSK) is analyzed for three types of phase detection system; differential detection, pilot-symbol-aided detection and pilot-tone-aided detection. A near-exact solution to the probability of event error in Rayleigh fading is derived, and two extremely tight upper bounds generated. They improve the Chernoff upper bound by at least a factor of four at medium and high signal-to-noise ratios (SNR)  相似文献   
77.
Metropolitan area networks (MANs) are well suited to serve as broadband multiplexers for asynchronous transfer mode (ATM) networks, to facilitate enterprise networking and to support future wireless personal communication systems. We propose and analyze a novel reservation arbitrated (RA) access method which provides isochronous voice transport over dual-bus MANs while enabling statistical multiplexing among voice calls. In combination with a new cyclic capturing (CC) mechanism, RA access allows stations to capture and reserve isochronous voice channels in a fair and distributive manner. This paper presents the RA access protocol, derives an analytical model for general waste-free voice reservation protocols, and analyzes the performance of RA access by computer simulations validated by analytical calculations. To assess the actual voice quality, simulation results based on a real voice signal are also presented. Results indicate that RA access offers significant improvements in channel utilization, as compared to prearbitrated (PA) access, while providing an acceptable quality of service. Therefore, RA access offers an efficient voice transport mechanism for existing switched multimegabit data service (SMDS) networks employing the IEEE 802.6 protocol, as well as emerging ATM/MAN-based broadband networks  相似文献   
78.
Noise limit in heterodyne Interferometer demodulator for FBG-based sensors   总被引:1,自引:0,他引:1  
This paper reports the results of a recent investigation on the noise-limited performance in heterodyne interferometric demodulation systems for fiber Bragg grating strain sensors. Theoretical and simulation results are presented and compared with experimental results.  相似文献   
79.
We observe bulk-like hole transport in amorphous organic semiconductors in a thin film transistor (TFT) configuration. Five different organic hole transporters (HTs) commonly used in organic light-emitting diodes are investigated. When these HTs are deposited on SiO2 gate dielectric layer, the TFT mobilities are 1–2 orders of magnitude smaller than those obtained from bulk films (3–8 μm) using time-of-flight (TOF) technique. The reduction of hole mobilities can be attributed to the interactions between the organic HTs and the polar SiO bonds on the gate dielectric layer. Detailed temperature dependence studies, employing the Gaussian disorder model, indicate that the SiO2 gate dielectric contributes between 60 and 90 meV of energetic disorder in the charge hopping manifold. Besides SiO2 gate dielectric, similar effects can also be observed for other polar insulators including polymeric PMMA and BCB, or HMDS-modified SiO2. However, when a common non-polar polymer, polystyrene (PS), is employed as the dielectric layer, the dipolar energetic disorder becomes negligible. Holes effectively experience bulk-like transport on the PS gate dielectric surface. TFT mobilities extracted from all five organic HTs are in excellent agreements with TOF mobilities. The present study should have broad applications in the transport characterization of amorphous organic semiconductors.  相似文献   
80.
This paper proposes a new digital beamformer for uniform concentric spherical array (UCSA) having nearly frequency invariant (FI) characteristics. The basic principle is to transform the received signals to the phase mode and remove the frequency dependency of the individual phase mode through the use of a digital beamforming network. It is shown that the far field pattern of the array is determined by a set of weights and it is approximately invariant over a wide range of frequencies. FI UCSAs are electronic steerable in both the azimuth and elevation angles, unlike their concentric circular array counterpart. The frequency invariant characteristic of the FI UCSA also makes it possible to design separately the compensation network and beamformer weighting coefficients. The design of the compensation network is formulated as a second order cone programming (SOCP) problem and is solved optimally for minimax criterion. Thanks to the frequency invariant characteristic, traditional narrow band adaptive beamforming algorithms such as minimum variance beamforming (MVB) can be applied to the FI UCSA. Also, traditional narrow band 2-D direction of arrival (DOA) estimation algorithms such as unitary ESPRIT can be extended to broadband DOA estimation using FI UCSA. Simulation results show that the proposed adaptive beamformer using FI UCSA can obtain a higher output signal to inference plus noise ratio over the conventional tapped-delay line approach. Simulation results also show that FI UCSA has uniform beampattern and resolution around 360° in both azimuth and elevation angles, unlike FI uniform concentric circular array. The usefulness of the proposed UCSA-FIB in broadband 2-D DOA estimation is also verified by computer simulation.
H. H. ChenEmail:
  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