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   1518315篇
  免费   25996篇
  国内免费   6995篇
电工技术   34674篇
综合类   6392篇
化学工业   272212篇
金属工艺   65061篇
机械仪表   43703篇
建筑科学   46273篇
矿业工程   11592篇
能源动力   50273篇
轻工业   112407篇
水利工程   15427篇
石油天然气   38022篇
武器工业   147篇
无线电   197788篇
一般工业技术   286501篇
冶金工业   166825篇
原子能技术   34206篇
自动化技术   169803篇
  2021年   15527篇
  2020年   11814篇
  2019年   14602篇
  2018年   16983篇
  2017年   16567篇
  2016年   21922篇
  2015年   17429篇
  2014年   28655篇
  2013年   87977篇
  2012年   35749篇
  2011年   49017篇
  2010年   43530篇
  2009年   52024篇
  2008年   45491篇
  2007年   43017篇
  2006年   44536篇
  2005年   40054篇
  2004年   41789篇
  2003年   41524篇
  2002年   40495篇
  2001年   37266篇
  2000年   35721篇
  1999年   34783篇
  1998年   45807篇
  1997年   39781篇
  1996年   35653篇
  1995年   30988篇
  1994年   28931篇
  1993年   28844篇
  1992年   26212篇
  1991年   23300篇
  1990年   23650篇
  1989年   22790篇
  1988年   21196篇
  1987年   19461篇
  1986年   18872篇
  1985年   22208篇
  1984年   22312篇
  1983年   20279篇
  1982年   19258篇
  1981年   19372篇
  1980年   18031篇
  1979年   18525篇
  1978年   17744篇
  1977年   17663篇
  1976年   18743篇
  1975年   16027篇
  1974年   15508篇
  1973年   15615篇
  1972年   13081篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Learning in multiple model adaptive control switch   总被引:1,自引:0,他引:1  
Including a learning mechanism in SMMAC (switched, multiple-model adaptive control) avoids the need for a priori knowledge of the model set of the plant to control and leads to a significant performance improvement with respect to the sole inclusion of an adaptive control channel in combination with switched fixed local controllers.  相似文献   
992.
The effects of parameter uncertainty on optimal policy have been a matter of interest for academics, and even for some policymakers, for a long time. Two lines of literature have developed analytical results on this matter. The first line uses static models and the second dynamic models. In this dynamic line most of the results are confined to models with a single state and a single control variable. In this paper we want to encourage the analysis of more general dynamic cases. To do so, the results in the dynamic line are extended from one-state and one-control finite horizon models to models with a pair of control variables. We then discuss some of the hurdles which must be surmounted for the results to be made more general and suggests some lines for further research. JEL classification: C61; E61  相似文献   
993.
A new and original method of calibrating helium leaks that makes it possible to take into account the existence of a number of auxiliary phenomena is described. For this purpose, a hollow leak the purpose of which is to reproduce only desorbed gas flows, is introduced into the vacuum system of the calibration bench. Analysis of the results of corresponding cumulation measurements makes it possible to introduce corrections for these phenomena.  相似文献   
994.
The growth of the Internet and of various intranets has spawned a wealth of online services, most of which are implemented on local-area clusters using remote invocation (for example, remote procedure call/remote method invocation) among manually placed application components. Component placement can be a significant challenge for large-scale services, particularly when application resource needs are workload dependent. Automatic component placement has the potential to maximize overall system throughput. The key idea is to construct (offline) a mapping between input workload and individual-component resource consumption. Such mappings, called component profiles, then support high-performance placement. Preliminary results on an online auction benchmark based on J2EE (Java 2 Platform, Enterprise Edition) suggest that profile-driven tools can identify placements that achieve near-optimal overall throughput.  相似文献   
995.
A new class of special effect pigments based on synthetically manufactured silica flakes coated with metal oxides was developed and introduced into the market. Silica flake pigments show extraordinary color effects such as improved interference and strong angle-dependent behavior. They can be used in automotive paints, industrial paints, plastics, and printing inks.  相似文献   
996.
A method of measuring and identifying the static parameters of a bipolar transistor is considered. The characteristic of the transistor, from which the parameters of the model are determined, is chosen depending on what group the calculated parameters belong to. The characteristics are measured in such a way that the equations of the model describing them can be reduced to the simplest form.  相似文献   
997.
998.
Using a corrected sum rule and a generalized virial identity, we study the analytical expression for entire modes of the collective elementary excitation spectrum in a trapped Bose–Einstein condensate at any atom number. Explicit analytical formulas for the spectrum are obtained for the harmonic traps with both spherical symmetry and axial symmetry using the gaussian approximation for the N-body ground-state wave function of the condensate. These formulas give the simple dependence of all energy levels on the atom numbers, their interaction strength and trap geometry parameters.  相似文献   
999.
Many cables containing 1.3-/spl mu/m zero-dispersion single-mode (SM) optical fibers are installed in trunk and access networks. Recently, there have been a number of studies on wavelength-division-multiplexing (WDM) systems designed to increase transmission capacity and flexibility. If we can construct WDM systems using SM optical-fiber cable networks designed to transmit using wavelengths in the 1.3-/spl mu/m window (O-band), this will prove very effective in reducing construction costs. It is therefore important to examine the wavelength dependence of the transmission characteristics of SM optical-fiber cables and networks that have already been installed and in which several optical fibers are joined. In this paper, we describe the measured optical characteristics of SM optical-fiber cables and installed optical-fiber cable networks at various wavelengths. The optical characteristics were stable in the 1.46 to 1.625-/spl mu/m wavelength range and we confirmed that the installed SM optical-fiber cable networks could be used for WDM system applications.  相似文献   
1000.
Advances in the fabrication of solid-solution single crystal relaxor ferroelectrics have made it possible to produce highly efficient piezoelectric crystals, and have attracted renewed interest in the use of these crystals for a new generation of piezoelectric transducers, actuators and sensors. Of particular interest is their incorporation into micro-electromechanical systems (MEMS). In this paper we report on the laser-induced wet chemical etching of lead zinc niobate-lead titanate (PZN-PT) in hydrochloric acid (HCl). Argon-ion laser radiation at power levels up to 4 W is focused to a spot diameter of about 15μm and results in the chemical etching of grooves at patterning speeds up to 5μm/sec. Crystal ion slicing, an ion-implant-based film separation technique, is used in combination with laser etching to form 5 to 10μm-thick patterned and freestanding films for incorporation into micro-electromechanical devices.  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