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   525910篇
  免费   7144篇
  国内免费   1471篇
电工技术   9568篇
综合类   526篇
化学工业   78825篇
金属工艺   19973篇
机械仪表   15232篇
建筑科学   12684篇
矿业工程   2274篇
能源动力   14541篇
轻工业   47104篇
水利工程   5226篇
石油天然气   9340篇
武器工业   37篇
无线电   59947篇
一般工业技术   101861篇
冶金工业   103591篇
原子能技术   10564篇
自动化技术   43232篇
  2022年   3176篇
  2021年   4920篇
  2020年   3497篇
  2019年   4581篇
  2018年   7828篇
  2017年   7632篇
  2016年   7963篇
  2015年   5575篇
  2014年   9264篇
  2013年   24122篇
  2012年   14657篇
  2011年   20174篇
  2010年   15831篇
  2009年   17733篇
  2008年   18109篇
  2007年   17792篇
  2006年   15520篇
  2005年   14222篇
  2004年   13609篇
  2003年   13404篇
  2002年   12645篇
  2001年   12839篇
  2000年   11872篇
  1999年   12603篇
  1998年   32836篇
  1997年   22916篇
  1996年   17469篇
  1995年   13041篇
  1994年   11289篇
  1993年   10982篇
  1992年   7918篇
  1991年   7421篇
  1990年   7264篇
  1989年   7015篇
  1988年   6472篇
  1987年   5766篇
  1986年   5657篇
  1985年   6266篇
  1984年   5900篇
  1983年   5175篇
  1982年   4902篇
  1981年   4970篇
  1980年   4705篇
  1979年   4609篇
  1978年   4408篇
  1977年   5335篇
  1976年   6975篇
  1975年   3797篇
  1974年   3550篇
  1973年   3665篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
A series of small–capacity units has recently been constructed in regions of oil field development and crude oil and gas condensate production to satisfy the requirements for such petroleum products as naphtha, diesel fuel, kerosene, and boiler fuel and to reduce costs for delivery of these products. There are almost no data in the technical literature, particularly in periodicals, on the construction and operation of small–capacity units. We attempt to generalize the experience of Orgeneftekhimzavody Trust in this area. We hope that this experience will be useful to specialists in the development and management of small–capacity plants.  相似文献   
42.
The interference issues related to ultrawideband (UWB) radio pose tight restrictions on the maximum data rate of UWB radio telecommunication systems. A possible solution is to reduce the required signal to interference ratio (SIR) that gives satisfactory performance to the UWB system. In this letter, we propose coded M-ary UWB radio communication systems. Two classes of convolutional codes, namely, low-rate superorthogonal codes and high-rate punctured codes are considered for this purpose. Simulation results on the bit error rate of the proposed system indicates that the system is capable to work in lower SIR's and therefore supports higher data transmission rates in a real interference environment compared to the previously proposed UWB communication systems.  相似文献   
43.
伊朗卡尔黑多目标水利枢纽,首台机组于2002年9月投运。介绍了工程历史,并从导流系统遂洪道、渗漏控制和惟幕灌浆等方面介绍了工程的技术要求。  相似文献   
44.
45.
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   
46.
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   
47.
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   
48.
Non‐isothermal processing of lignocellulosic materials in aqueous media (autohydrolysis reaction) under mild conditions leads to solutions containing valuable chemicals (oligosaccharides, sugars and acetic acid) and other, undesired, compounds (belonging to the extractive and acid‐soluble lignin fractions) which have to be removed in further purification treatments. Liquors obtained by non‐isothermal autohydrolysis of Eucalyptus globulus wood and corncobs under a variety of operational conditions were extracted with ethyl acetate in order to remove non‐saccharide components, and the suitability of the fraction dissolved in the organic phase was assayed for possible utilisation as an antioxidant. The yield and antioxidant activity of ethyl acetate extracts (measured by the α,α‐diphenyl‐β‐picrylhydrazyl (DPPH) radical scavenging capacity) showed a strong dependence on the autohydrolysis conditions. The antioxidant activity of extracts obtained under selected operational conditions compared well with synthetic antioxidants. © 2003 Society of Chemical Industry  相似文献   
49.
Si3N4 ceramic was jointed to itself using a filler alloy of Cu76.5Pd8.5Ti15, and the mechanical properties of the jointwere measured and analyzed. By using a filler alloy of Cu76.5Pd8.5Ti15, the SisN4/SisN4 joints were obtained bybrazing at 1373~1473 K f  相似文献   
50.
A model is formulated that describes how radiation-induced charge accumulates in the gate oxide of a MOS structure and how it decays through tunneling and thermal emission. The model is used in a numerical analysis of the x-ray or UV adjustment of threshold voltage in MOS-circuit manufacture. The limits of this process technique are evaluated.  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