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   566281篇
  免费   6702篇
  国内免费   1003篇
电工技术   10508篇
综合类   466篇
化学工业   90042篇
金属工艺   23335篇
机械仪表   18497篇
建筑科学   12528篇
矿业工程   4312篇
能源动力   14429篇
轻工业   45756篇
水利工程   6941篇
石油天然气   14961篇
武器工业   39篇
无线电   60277篇
一般工业技术   116227篇
冶金工业   95565篇
原子能技术   14681篇
自动化技术   45422篇
  2021年   5481篇
  2019年   5268篇
  2018年   9201篇
  2017年   9408篇
  2016年   9831篇
  2015年   6025篇
  2014年   10243篇
  2013年   26101篇
  2012年   15772篇
  2011年   21088篇
  2010年   16969篇
  2009年   18817篇
  2008年   19067篇
  2007年   18767篇
  2006年   16286篇
  2005年   14742篇
  2004年   14008篇
  2003年   13691篇
  2002年   13246篇
  2001年   12850篇
  2000年   12330篇
  1999年   12013篇
  1998年   27651篇
  1997年   20040篇
  1996年   15627篇
  1995年   12007篇
  1994年   10859篇
  1993年   10613篇
  1992年   8332篇
  1991年   8102篇
  1990年   7991篇
  1989年   7763篇
  1988年   7478篇
  1987年   6747篇
  1986年   6533篇
  1985年   7390篇
  1984年   6700篇
  1983年   6437篇
  1982年   5776篇
  1981年   5896篇
  1980年   5630篇
  1979年   5733篇
  1978年   5664篇
  1977年   6178篇
  1976年   7685篇
  1975年   5108篇
  1974年   4903篇
  1973年   4980篇
  1972年   4279篇
  1971年   4038篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
221.
Mössbauer effect measurements and physicochemical analysis demonstrate that annealing of amorphous Fe–P–Mn alloys leads to the formation of a nanocrystalline structure.  相似文献   
222.
One of the ultimate miniaturizations in nanotechnology is molecular electronics, where devices will consist of individual molecules. There are many complications associated with the use of molecules in electronic devices, such as the electronic perturbations in the molecule associated with being bonded to an electrode, how electrons traverse the metal-molecule junction, and the difficulty of macroscopically addressing single to very few molecules. Whether fabricating a test structure or a usable device, the use of self-assembly is fundamental to the fabrication of molecular electronic devices. We will discuss how to fabricate self-assembled monolayers into test assemblies and how to use intermolecular interactions to direct molecules into desired positions to create nanostructures and to connect functional molecules to the outside world. These assemblies serve as test structures for measurements on single or bundled molecules. The development of several experimental techniques, including various scanning probes, mercury drop junctions, break junctions, nanopores, crossed wires, and other techniques using nanoparticles have enabled the ability to test these structures and make reproducible measurements on single molecules. Many of these methods have been developed to test molecules with potential for integration into devices such as oligo (phenylene-ethynylene) molecules and other /spl pi/-conjugated molecules, in ensemble or single-molecule measurements.  相似文献   
223.
This paper considers several aspects of the sequential prediction problem for unbounded, nonstationary processes under pth power loss /spl lscr//sub p/(u,v)=|u-v|/sup p/, 1相似文献   
224.
225.
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   
226.
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   
227.
Reducible rank codes and their applications to cryptography   总被引:2,自引:0,他引:2  
We present a new family of so-called reducible rank codes which are a generalization of rank product codes . This family includes maximal rank distance (MRD) codes for lengths n>N in the field F/sub N/. We give methods for encoding and decoding reducible rank codes. A public key cryptosystem based on these codes and on the idea of a column scrambler is proposed. The column scrambler "mixes" columns of a generator (parity-check) matrix of a code. It makes the system more resistant to structural attacks such as Gibson's attacks. Possible attacks on the system are thoroughly studied. The system is found to be secure against known attacks for public keys of about 16 kbits and greater.  相似文献   
228.
This paper presents a method to obtain an electric model for transformers and inductors, including both frequency and geometry effects in the windings, which can be linked with existing core models. One-dimensional distributions for magnetic and electric fields are assumed, and from Maxwell's equations an equivalent electric circuit is easily obtained. This equivalent circuit has been included in analog simulators (Spice, AnalogWorkBench, Saber ...), and comparisons between measured and simulated results are shown, both in time domain and in AC sweep, which verify the model accuracy. The model described in this paper allows designers to deal with key issues in the design of high-frequency magnetic components (copper losses, leakage inductance, skin and proximity effects) by using analog simulators, which are usually more familiar to them than finite-element analysis tools.  相似文献   
229.
230.
This study examined reciprocal relationships between collective efficacy and team performance over a season of competition in women's intercollegiate ice hockey within weekends where the opponent was constant for 2 games. Collective efficacy beliefs within 12 teams were assessed prior to both games for at least 7 weekends. Team performance indexes produced an overall measure of performance for each game. The average influence of Saturday collective efficacy on Saturday performance was moderate and positive after controlling for Friday performance. The average influence of Friday performance on Saturday collective efficacy was small and positive after removing the influence of Friday collective efficacy from Friday performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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