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   5755篇
  免费   368篇
  国内免费   50篇
电工技术   103篇
综合类   16篇
化学工业   1598篇
金属工艺   162篇
机械仪表   227篇
建筑科学   174篇
矿业工程   16篇
能源动力   416篇
轻工业   609篇
水利工程   69篇
石油天然气   88篇
无线电   549篇
一般工业技术   971篇
冶金工业   248篇
原子能技术   60篇
自动化技术   867篇
  2024年   19篇
  2023年   103篇
  2022年   237篇
  2021年   351篇
  2020年   302篇
  2019年   353篇
  2018年   429篇
  2017年   347篇
  2016年   405篇
  2015年   222篇
  2014年   349篇
  2013年   599篇
  2012年   347篇
  2011年   373篇
  2010年   279篇
  2009年   243篇
  2008年   163篇
  2007年   105篇
  2006年   122篇
  2005年   75篇
  2004年   75篇
  2003年   58篇
  2002年   60篇
  2001年   28篇
  2000年   33篇
  1999年   21篇
  1998年   66篇
  1997年   41篇
  1996年   44篇
  1995年   32篇
  1994年   28篇
  1993年   27篇
  1992年   26篇
  1991年   19篇
  1990年   14篇
  1989年   24篇
  1988年   13篇
  1987年   15篇
  1986年   8篇
  1985年   12篇
  1984年   10篇
  1983年   9篇
  1982年   8篇
  1981年   10篇
  1980年   11篇
  1979年   8篇
  1978年   9篇
  1977年   8篇
  1976年   13篇
  1971年   4篇
排序方式: 共有6173条查询结果,搜索用时 10 毫秒
61.
Mortazavi  Seyed Hassan  Akbar  Reza  Safaei  Farshad  Rezaei  Amin 《Wireless Networks》2019,25(6):3675-3687
Wireless Networks - The combination of traditional wired links for regular transmissions and express wireless paths for long distance communications is a promising solution to prevent multi-hop...  相似文献   
62.
Thermoelectric effect spectroscopy and photoluminescence techniques were used to study the defect levels in samples from three crystals of CdTe:In grown by the vertical gradient freeze method. The main goal of the investigation was to study defects, which strongly trap charge carriers or act as recombination centers in order to eliminate them from the technological process. The main difference among detecting and non-detecting samples was the absence of electron traps with a very high capture cross-section and energy 0.6 eV to 0.7 eV, which act as lifetime killers even at low concentrations. Recently published ab initio calculations show a complex of Te antisite and Cd vacancy within this energy range.  相似文献   
63.
The ever increasing demand of security has resulted in wide use of Biometric systems. Despite overcoming the traditional verification problems, the unimodal systems suffer from various challenges like intra class variation, noise in the sensor data etc, affecting the system performance. These problems are effectively handled by multimodal systems. In this paper, we present multimodal approach for palm- and fingerprints by feature level and score level fusions (sum and product rules). The proposed multi-modal systems are tested on a developed database consisting of 440 palm- and fingerprints each of 55 individuals. In feature level fusion, directional energy-based feature vectors of palm- and fingerprint identifiers are combined to form joint feature vector that is subsequently used to identify the individual using a distance classifier. In score level fusion, the matching scores of individual classifiers are fused by sum and product rules. Receiver operating characteristics curves are formed for unimodal and multimodal systems. Equal Error Rate (EER) of 0.538% for feature level fusion shows best performance compared to score level fusion of 0.6141 and 0.5482% of sum and product rules, respectively. Multimodal systems, however, significantly outperform unimodal palm- and fingerprints identifiers with EER of 2.822 and 2.553%, respectively.  相似文献   
64.
Sulfur‐doped graphene (SG) is prepared by a thermal shock/quench anneal process and investigated as a unique Pt nanoparticle support (Pt/SG) for the oxygen reduction reaction (ORR). Particularly, SG is found to induce highly favorable catalyst‐support interactions, resulting in excellent half‐cell based ORR activity of 139 mA mgPt ?1 at 0.9 V vs RHE, significant improvements over commercial Pt/C (121 mA mgPt ?1) and Pt‐graphene (Pt/G, 101 mA mgPt ?1). Pt/SG also demonstrates unprecedented stability, maintaining 87% of its electrochemically active surface area following accelerated degradation testing. Furthermore, a majority of ORR activity is maintained, providing 108 mA mgPt ?1, a remarkable 171% improvement over Pt/C (39.8 mA mgPt ?1) and an 89% improvement over Pt/G (57.0 mA mgPt ?1). Computational simulations highlight that the interactions between Pt and graphene are enhanced significantly by sulfur doping, leading to a tethering effect that can explain the outstanding electrochemical stability. Furthermore, sulfur dopants result in a downshift of the platinum d‐band center, explaining the excellent ORR activity and rendering SG as a new and highly promising class of catalyst supports for electrochemical energy technologies such as fuel cells.  相似文献   
65.
In this paper, a novel universal receiver baseband approach is introduced. The chain includes a post-mixer noise shaping blocker pre-filter, a programmable-gain post mixer amplifier (PMA) with blocker suppression, a differential ramp-based novel linear-in-dB variable gain amplifier and a Sallen–Key output buffer. The 1.2-V chain is implemented in a 65-nm CMOS process, occupying a die area of 0.45 mm2. The total power consumption of the baseband chain is 11.5 mW. The device can be tuned across a bandwidth of 700-KHz to 5.2-MHz with 20 kHz resolution and is tested for two distinct mobile-TV applications; integrated services digital broadcasting-terrestrial ISDB-T (3-segment f c = 700 kHz) and digital video broadcasting-terrestrial/handheld (DVB-T/H f c = 3.8 MHz). The measured IIP3 of the whole chain for the adjacent blocker channel is 24.2 and 24 dBm for the ISDB-T and DVB-T/H modes, respectively. The measured input-referred noise density is 10.5 nV/sqrtHz in DVB-T/H mode and 14.5 nV/sqrtHz in ISDB-T mode.  相似文献   
66.
Rain attenuation is the dominant propagation impairment for satellite communication systems operating at frequencies above about 10 GHz. The rainfall path attenuation at 12.255 GHz measured at Universiti Sains Malaysia (USM) for 4 years (2 January to 5 December) is presented. This paper presents an empirical analysis of rain rate and rain attenuation cumulative distribution functions obtained using 1‐min integrated rainfall data and comparison of the measured data with data obtained from well‐established rain model attenuation predictions. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   
67.
This paper proposes a novel method for camera calibration using images of a mirror symmetric object. Assuming unit aspect ratio and zero skew, we show that interimage homographies can be expressed as a function of only the principal point. By minimizing symmetric transfer errors, we thus obtain an accurate solution for the camera parameters. We also extend our approach to a calibration technique using images of a 1-D object with a fixed pivoting point. Unlike existing methods that rely on orthogonality or pole-polar relationship, our approach utilizes new inter-image constraints and does not require knowledge of the 3-D coordinates of feature points. To demonstrate the effectiveness of the approach, we present results for both synthetic and real images.  相似文献   
68.
This paper presents a software-based error detection scheme called enhanced committed instructions counting (ECIC) for embedded and real-time systems using commercial off-the-shelf (COTS) processors. The scheme uses the internal performance monitoring features of a processor, which provides the ability to count the number of committed instructions in a program. To evaluate the ECIC scheme, 6000 software induced faults are injected into a 32-bit Pentium® processor. The results show that the error detection coverage varies between 90.52% and 98.18%, for different workloads.  相似文献   
69.
In this work, we introduce a new spectrum leasing based cognitive radio for OFDM-based primary/secondary networks. More precisely, we propose a new leasing scheme both in time and frequency domains in a network composed of a primary transmission and some secondary (cognitive) users forming a cooperative relay network. In the proposed scheme, the primary user decides to lease a part of its available resources (time and frequency) to a selected set of relays, with the aim of increasing its link reliability. The selected relays use a part of the leased resources for relaying the primary signal, and in counterpart, they are allowed to exploit the rest of the frame for their own data transmission. By defining appropriate cost functions, the proposed algorithm decides whether it is of advantage for the primary user to cooperate with the relay network or not. Moreover, if cooperation is advantageous for the primary network, the algorithm selects the optimal amount of the time-frequency resources (number of OFDM symbols and subcarriers) that are involved in the cooperation process. Simulation results show that by using the proposed relaying scheme, both primary and secondary (relay) networks can take advantage in terms of achievable data rates compared to classical leasing systems.  相似文献   
70.
A programmable high-speed source-series-terminated driver with signal boost capability is presented. The driver uses only one main input data tap and is divided into main units and auxiliary units. A passive high pass filter is utilized to detect data transitions and control the inputs of the auxiliary units to enable a programmable amplitude boost for the output signal. The corner frequency of the high pass filter is adjusted depending on the data rate. Further, the amount of the high frequency signal boost can be adjusted depending on the loss of the channel. HSPICE simulations are used to demonstrate the performance of the driver at 10, 20 and 40 Gbps data rates. At 40 Gbps, the driver is capable of equalizing a PRBS9 data pattern signal through a channel that has a loss of 9 dB. At worst case conditions and 40 Gbps date rate, the driver achieves a differential eye-opening amplitude of 201 mVppd and an eye-opening of 0.952 UI. The driver is designed using 28 nm CMOS process and uses a nominal 1 V supply voltage. It consumes a maximum of 12 mW of at-speed power.  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