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   8929篇
  免费   750篇
  国内免费   16篇
电工技术   121篇
综合类   15篇
化学工业   2148篇
金属工艺   350篇
机械仪表   431篇
建筑科学   135篇
矿业工程   3篇
能源动力   348篇
轻工业   915篇
水利工程   35篇
石油天然气   7篇
武器工业   1篇
无线电   1527篇
一般工业技术   2110篇
冶金工业   594篇
原子能技术   83篇
自动化技术   872篇
  2024年   11篇
  2023年   134篇
  2022年   196篇
  2021年   330篇
  2020年   232篇
  2019年   232篇
  2018年   315篇
  2017年   337篇
  2016年   408篇
  2015年   354篇
  2014年   465篇
  2013年   639篇
  2012年   649篇
  2011年   841篇
  2010年   587篇
  2009年   550篇
  2008年   449篇
  2007年   390篇
  2006年   325篇
  2005年   259篇
  2004年   263篇
  2003年   220篇
  2002年   165篇
  2001年   153篇
  2000年   158篇
  1999年   137篇
  1998年   230篇
  1997年   127篇
  1996年   105篇
  1995年   57篇
  1994年   64篇
  1993年   46篇
  1992年   36篇
  1991年   23篇
  1990年   23篇
  1989年   24篇
  1988年   16篇
  1987年   10篇
  1986年   15篇
  1985年   7篇
  1984年   10篇
  1983年   11篇
  1981年   6篇
  1980年   7篇
  1979年   6篇
  1977年   7篇
  1976年   9篇
  1974年   7篇
  1971年   7篇
  1970年   6篇
排序方式: 共有9695条查询结果,搜索用时 11 毫秒
71.
In Europe, the challenge of the design of third-generation cellular mobile radio systems has been taken numerous research and development activities in this field have been started. The authors try to give an overview of the European activities in this field. The article is organized in two parts. In the first part, the requirements for third-generation cellular mobile radio systems such as Universal Mobile Telecommunications System (UMTS) and Future Public Land Mobile Telecommunications System (FPLMTS), which has been named International Mobile Telecommunications after the year 2000 (IMT-2000) are presented concisely. Also, the importance and challenge of the multiple access design for such third-generation cellular mobile radio systems is explained. In the second part, numerous European research activities with focus on the multiple access design for third-generation cellular mobile radio systems are reviewed  相似文献   
72.
The main goal of this article is to present the translation of quality of service (QoS) parameters between layers. The QoS parameters in the ATM layer and AAL are defined. This translation concept came from the QoS framework in which the influence of the protocol stack on the QoS should be considered. As an example, we concentrate on the translation from the AAL to the ATM layer, as the AAL must be designed to be service-dependent and specific. Translation, both taking the transport protocol into account as well as between application and transport QoS, needs further study. However, our study shows that the QoS translation is a possible and good approach in end-to-end QoS guarantees in the broadband integrated services digital network (B-ISDN). As far as the end-to-end QoS guarantee issue is concerned, the transport QoS requirements are specified in terms of bounds on transport QoS parameters. The bounds on transport QoS parameters will be translated into the bounds on ATM layer QoS parameters. The ATM-layer QoS parameters resulting from the translation will be the performance requirements on a connection basis for the ATM network, but are basically the end-to-end parameters, including the network and the end systems. Therefore, the QoS translation finally results in the network performance parameters in the ATM network. We define QoS parameters in the AAL and ATM layer. Case studies in which the translation method is applied to a constant bit rate (CBR) video service and data service, respectively, are also presented  相似文献   
73.
Core-shell-type nanoparticles with TiO2 cores and CaCO3 shells were applied as the electrode of dye-sensitized solar cells. The performance of the cell was significantly improved (as high as 26.7%) compared to the case when un-coated TiO2 particle film was used as electrode. The improved energy conversion efficiency has been ascribed to (i) enhanced dye adsorption due to the high isoelectric point of the overlayer, and (ii) the prevention of the back electron transfer by the insulating nature of the overlayer.  相似文献   
74.
Power generation characteristics of a sandwich‐type thermoelectric generator in which the heat source is embedded into thermoelectric elements are investigated. Our previous work on a similar concept only considered a uniform heat source distribution inside thermoelectric elements. In this work, the effect of the spatial distribution of a heat source is examined. In particular, the effect of the concentration of heat source near the one end, that is, the hot end, is intensively studied as a potential means of improving the efficiency of the device. Although the effects of heat source concentration in impractical cases without heat transfer limitations on the cold side remain ambiguous, it become clear that heat source concentration indeed has positive effects in more realistic cases with finite heat transfer coefficients imposed on the cold side. Because of the relatively low efficiency of typical thermoelectric generation, a significant amount of heat must be dissipated from the cold end of the thermoelectric element. Greater heat source concentration near the hot end leads to more effective utilization of available heat source, reduces the amount of heat rejected at the cold end, and lowers the hot end temperature of the thermoelectric element. Overall, it is suggested that heat source concentration can be used as a method to achieve more efficient operation and better structural integrity of the system. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
75.
The reduction of carbon dioxide (CO2) into chemical feedstock is drawing increasing attention as a prominent method of recycling atmospheric CO2. Although many studies have been devoted in designing an efficient catalyst for CO2 conversion with noble metals, low selectivity and high energy input still remain major hurdles. One possible solution is to use the combination of an earth‐abundant electrocatalyst with a photoelectrode powered by solar energy. Herein, for the first time, a p‐type silicon nanowire with nitrogen‐doped graphene quantum sheets (N‐GQSs) as heterogeneous electrocatalyst for selective CO production is demonstrated. The photoreduction of CO2 into CO is achieved at a potential of ?1.53 V versus Ag/Ag+, providing 0.15 mA cm?2 of current density, which is 130 mV higher than that of a p‐type Si nanowire decorated with well‐known Cu catalyst. The faradaic efficiency for CO is 95%, demonstrating significantly improved selectivity compared with that of bare planar Si. The density functional theory (DFT) calculations are performed, which suggest that pyridinic N acts as the active site and band alignment can be achieved for N‐GQSs larger than 3 nm. The demonstrated high efficiency of the catalytic system provides new insights for the development of nonprecious, environmentally benign CO2 utilization.  相似文献   
76.
Digital predistorter using multiple lookup tables   总被引:1,自引:0,他引:1  
Jung  W.J. Kim  W.R. Kim  K.M. Lee  K.B. 《Electronics letters》2003,39(19):1386-1388
A new digital predistorter is proposed that copes with the variation of power amplifier characteristics faster than the adaptation rate of the predistorter by using multiple lookup tables. Experimental results derived from a prototype show that the proposed predistorter can suppress the adjacent channel interference up to 12 dB compared to the conventional predistorter with a single lookup table.  相似文献   
77.
Antimony triselenide (Sb2Se3) nanoflake-based nitrogen dioxide (NO2) sensors exhibit a progressive bifunctional gas-sensing performance, with a rapid alarm for hazardous highly concentrated gases, and an advanced memory-type function for low-concentration (<1 ppm) monitoring repeated under potentially fatal exposure. Rectangular and cuboid shaped Sb2Se3 nanoflakes, comprising van der Waals planes with large surface areas and covalent bond planes with small areas, can rapidly detect a wide range of NO2 gas concentrations from 0.1 to 100 ppm. These Sb2Se3 nanoflakes are found to be suitable for physisorption-based gas sensing owing to their anisotropic quasi-2D crystal structure with extremely enlarged van der Waals planes, where they are humidity-insensitive and consequently exhibit an extremely stable baseline current. The Sb2Se3 nanoflake sensor exhibits a room-temperature/low-voltage operation, which is noticeable owing to its low energy consumption and rapid response even under a NO2 gas flow of only 1 ppm. As a result, the Sb2Se3 nanoflake sensor is suitable for the development of a rapid alarm system. Furthermore, the persistent gas-sensing conductivity of the sensor with a slow decaying current can enable the development of a progressive memory-type sensor that retains the previous signal under irregular gas injection at low concentrations.  相似文献   
78.
We demonstrate a novel all-fiber gap-type tunable bandpass filter configuration that consists of a broadband hollow optical fiber (HOF) acoustooptic tunable filter (AOTF) concatenated with a narrowband single-mode fiber (SMF)-AOTF. Owing to the unique mode coupling properties of HOF-AOTF and SMF-AOTF, a narrow passband channel of a full-width at half-maximum (FWHM) of ~4 nm could be formed in a broad stopband platform of a 90-nm FWHM successfully. In this scheme, the center wavelength and rejection efficiency of both passband and stopband were found to be flexibly tunable by adjusting the frequency and the voltage of radio-frequency signals applied to individual acoustic transducers.  相似文献   
79.
To improve the propagation loss of polymer-based long-range surface-plasmon-polariton (LR-SPP) waveguide devices at the telecom wavelength range, low-loss LR-SPP waveguides were fabricated in an ultraviolet-curable acrylate polymer with a low refractive index and absorption loss. A propagation loss of 1.72 dB/cm at a wavelength of 1.55 mum was achieved with a 14-nm-thick and 3-mum-wide metal stripe.  相似文献   
80.
We propose and demonstrate a new structure of a Data Vortex switch node for all-optical routing of wavelength-division-multiplexing (WDM) 10-Gb/s optical packets. The proposed node consists of two Mach-Zehnder interferometers with integrated semiconductor optical amplifier: an optical and gate and a high-speed optical switch. In the experiment, WDM 10-Gb/s data packets are successfully routed with 1-dB power penalty at a bit-error rate of 10-9.  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