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   1503篇
  免费   23篇
  国内免费   3篇
电工技术   84篇
综合类   2篇
化学工业   437篇
金属工艺   60篇
机械仪表   33篇
建筑科学   22篇
能源动力   98篇
轻工业   129篇
水利工程   9篇
石油天然气   1篇
无线电   124篇
一般工业技术   265篇
冶金工业   63篇
原子能技术   47篇
自动化技术   155篇
  2023年   6篇
  2022年   16篇
  2021年   21篇
  2020年   13篇
  2019年   23篇
  2018年   14篇
  2017年   14篇
  2016年   27篇
  2015年   18篇
  2014年   51篇
  2013年   119篇
  2012年   81篇
  2011年   83篇
  2010年   76篇
  2009年   93篇
  2008年   88篇
  2007年   69篇
  2006年   58篇
  2005年   53篇
  2004年   39篇
  2003年   52篇
  2002年   43篇
  2001年   25篇
  2000年   34篇
  1999年   38篇
  1998年   46篇
  1997年   21篇
  1996年   31篇
  1995年   18篇
  1994年   18篇
  1993年   21篇
  1992年   23篇
  1991年   16篇
  1990年   12篇
  1989年   16篇
  1988年   12篇
  1987年   5篇
  1986年   10篇
  1985年   15篇
  1984年   11篇
  1983年   7篇
  1982年   9篇
  1981年   15篇
  1980年   16篇
  1979年   9篇
  1978年   11篇
  1977年   10篇
  1976年   5篇
  1974年   4篇
  1967年   3篇
排序方式: 共有1529条查询结果,搜索用时 111 毫秒
1.
Electric power systems are expanding in size and complexity, and the requirement for the energy management system (EMS) is becoming more important. In this computer control system, a single control computer is used mainly as the primary computer and its software is very complicated because of its hugh number of small, quick tasks to obtain high response speed. Therefore, much effort is needed to develop and modify the programs, and the responsiveness of this centralized architecture varies greatly when many faults occur in the power system. This paper describes a new distributed architecture for the EMS. Distributed processors execute the functions cooperatively with periodic access to the common bulletin board database in which information about the power system exist. This architecture facilitates the software development and maintenance, and it also enhances the performance by the parallel processing of the distributed functions.  相似文献   
2.
When a fault occurs on transmission or distribution systems due to lightning or overvoltage, often an arc discharge occurs at the fault point. The arc discharge, which is caused by a fault current, has a high current, high temperature, strong light emission, etc., thus it sometimes causes heavy damages to electric power equipment. The arc discharge is influenced by the conditions around the arcs, i.e., gas, insulation materials, gap length, weather, etc. Also, the arc voltage along the arc column indicates the characteristics of the arc. If the voltage waveforms of the arcs caused by the fault on transmission or distribution systems are classified, it is possible to find the location and the equipment where the fault occurred. In this paper, the arc voltage data in 6-kV class XLPE cables and 6-kV class overhead lines are analyzed and an artificial neural network method is applied to classify the arc voltage waveforms. The results obtained from the six artificial neural networks developed show that the artificial neural network method is effective for classification of arc voltage waveforms if adequate input parameters are selected.  相似文献   
3.
The wax esters of sperm whale head oil have been characterized by gas-liquid chromatography on an APOLAR 10C column according to their carbon number and number of double bonds. The novel technique permits the direct quantitative analysis of saturated and unsaturated wax esters.  相似文献   
4.
This paper aims to understand the solder bump electromigration phenomenon in the Cu/Sn–3Ag–0.5Cu/Cu system. A temperature of 453 K with a current density of 10 kA/cm2 was applied. A void nucleated at the highest current density point at the cathode. As the void grew along the cathode side, a solder depletion occurred on the opposite side of the electron entry point, resulting in an open failure. A unique purposely-designed 3D model simulation methodology provides a good understanding of the void nucleation and growth behavior. The temperature of the solder joint during the electromigration test was measured successfully by the resistance change in the junction line between the two joints.  相似文献   
5.
The tunnel injection transit time (TUNNETT) diodes with p+p+n+nn+ structure were fabricated by liquid phase epitaxy (LPE). About 100 Å tunnel junction (p+n+) was successfully prepared by the double impurity diffusion of Ge and S during LPE growth. Continuous wave (CW) oscillation was realized at 51.520 GHz in the V-band cavity with the phase noise of −60 dBc/Hz at 1 kHz bandwidth.  相似文献   
6.
Low-temperature (290°C) area-selective regrowth by molecular layer epitaxy (MLE) was applied for the fabrication of an ultra-shallow sidewall (50 nm) GaAs tunnel junction. Fabricated tunnel junctions have shown a record peak current density up to 35,000 A/cm2. It is shown that the tunnel junction characteristics are strongly dependent on the sidewall orientation and the AsH3 surface treatment conditions just prior to regrowth. The effects of AsH3 surface treatment are discussed in view of the control of surface stoichiometry.  相似文献   
7.
A bare LSI chip mounted onto a flexible substrate is called chip-on-flex (COF). Companies and universities are desperately developing COF. In this paper, the development of COF using stud bump bonding (SBB) flip-chip technology will be introduced.So far, SBB technology has been adopted when ceramic or glass-epoxy is used as a substrate material for chip size packages (CSPs) and multi-chip modules (MCMs). Recently there is a great demand for developing SBB technology toward a flexible substrate.SBB technology needs to keep a flexible substrate flat during the assembly process. A flexible substrate was adhered to a flat carrier using a thermal release sheet in order to keep it flat. Since this thermal release sheet loses its adhesive strength by applying heat beyond 160°C, it is easy to peel off accomplished specimens from the flat carrier after assembling.SBB specimens were prepared using liquid crystal polymer (LCP) and polyimide (PI) as a flexible substrate. Reliability tests, such as pressure cooker test (PCT), thermal shock test (TST) and reflow soldering after moisture storage test, were carried out for these specimens. In PCT, both LCP and PI specimens passed as a result of using proper underfill for each substrate. In TST, both specimens also passed using the underfill selected in PCT. In reflow soldering after moisture storage test, LCP specimens passed, on the other hand PI specimens needed to be baked after moisture storage in order to pass the reflow.  相似文献   
8.
9.
In this paper, we analyse the message waiting times in a local area network (LAN) that uses the demand‐priority access method. This is a priority‐based round‐robin arbitration method where the central controller (the repeater) polls its connected ports to determine which have transmission requests pending and the requests' priority classes. We model it as a 2‐priority M/G/1 queue with multiple server vacations and switchover time between service periods. The service discipline is nonpreemptive and the length of the switchover time is dependent upon the priority class of the preceding message served as well as that of the message to be served next. We provide an approximate analysis for the waiting times of both message classes and derive expressions for the Laplace–Stieltjes transforms (LST) of the stationary distributions and the mean waiting times. We conclude with numerical and simulation results to show the applicability and accuracy of the analytical model. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   
10.
The homomorphic filtering method is described for the detection and quantitation of left-to-right shunts from radionuclide angiocardiography. First, the method is investigated theoreticatly and numerically using a realistic model with systemic recirculation. It is demonstrated that even in a noisy situation the shunt flow fraction can be relatively well estimated, if only the characteristics of the fiters used are suitable. Second, the method is applied to real data, i.e., the pulmonary time-activity curves from radionucUde anglocardiography. The presence or absence of a left-to-right shunt is determined using the ratio AT/MTT. The pulmonary-to-systemic flow ratios calculated from the areas of the two decomposed curves are compared with those from oximetry at cardiac catheterization. Good agreement between the Qp/Qs ratios calculated by oximetry and radionucUide angiocardiography is obtained.  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