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   526851篇
  免费   7154篇
  国内免费   1470篇
电工技术   9648篇
综合类   527篇
化学工业   78814篇
金属工艺   19983篇
机械仪表   15213篇
建筑科学   12739篇
矿业工程   2271篇
能源动力   14525篇
轻工业   47150篇
水利工程   5226篇
石油天然气   9336篇
武器工业   37篇
无线电   59971篇
一般工业技术   101911篇
冶金工业   104134篇
原子能技术   10574篇
自动化技术   43416篇
  2022年   3170篇
  2021年   4911篇
  2020年   3487篇
  2019年   4570篇
  2018年   7838篇
  2017年   7626篇
  2016年   7952篇
  2015年   5572篇
  2014年   9274篇
  2013年   24167篇
  2012年   14677篇
  2011年   20202篇
  2010年   15853篇
  2009年   17741篇
  2008年   18162篇
  2007年   17828篇
  2006年   15541篇
  2005年   14254篇
  2004年   13633篇
  2003年   13433篇
  2002年   12673篇
  2001年   12851篇
  2000年   11890篇
  1999年   12630篇
  1998年   32918篇
  1997年   22959篇
  1996年   17491篇
  1995年   13071篇
  1994年   11311篇
  1993年   11018篇
  1992年   7938篇
  1991年   7433篇
  1990年   7287篇
  1989年   7039篇
  1988年   6487篇
  1987年   5786篇
  1986年   5671篇
  1985年   6287篇
  1984年   5917篇
  1983年   5187篇
  1982年   4914篇
  1981年   4973篇
  1980年   4716篇
  1979年   4625篇
  1978年   4423篇
  1977年   5355篇
  1976年   6995篇
  1975年   3806篇
  1974年   3554篇
  1973年   3678篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
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   
62.
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   
63.
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   
64.
65.
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   
66.
67.
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   
68.
69.
In this paper, we describe a method for increasing the external efficiency of polymer light‐emitting diodes (LEDs) by coupling out waveguided light with Bragg gratings. We numerically model the waveguide modes in a typical LED structure and demonstrate how optimizing layer thicknesses and reducing waveguide absorption can enhance the grating outcoupling. The gratings were created by a soft‐lithography technique that minimizes changes to the conventional LED structure. Using one‐dimensional and two‐dimensional gratings, we were able to increase the forward‐directed emission by 47 % and 70 %, respectively, and the external quantum efficiency by 15 % and 25 %.  相似文献   
70.
Efficient blue‐, green‐, and red‐light‐emitting organic diodes are fabricated using binuclear platinum complexes as phosphorescent dopants. The series of complexes used here have pyrazolate bridging ligands and the general formula CNPt(μ‐pz)2PtCN (where CN = 2‐(4′,6′‐difluorophenyl)pyridinato‐N,C2′, pz = pyrazole ( 1 ), 3‐methyl‐5‐tert‐butylpyrazole ( 2 ), and 3,5‐bis(tert‐butyl)pyrazole ( 3 )). The Pt–Pt distance in the complexes, which decreases in the order 1 > 2 > 3 , solely determines the electroluminescence color of the organic light‐emitting diodes (OLEDs). Blue OLEDs fabricated using 8 % 1 doped into a 3,5‐bis(N‐carbazolyl)benzene (mCP) host have a quantum efficiency of 4.3 % at 120 Cd m–2, a brightness of 3900 Cd m–2 at 12 V, and Commission Internationale de L'Eclairage (CIE) coordinates of (0.11, 0.24). Green and red OLEDs fabricated with 2 and 3 , respectively, also give high quantum efficiencies (~ 6.7 %), with CIE coordinates of (0.31, 0.63) and (0.59, 0.46), respectively. The current‐density–voltage characteristics of devices made using dopants 2 and 3 indicate that hole trapping is enhanced by short Pt–Pt distances (< 3.1 Å). Blue electrophosphorescence is achieved by taking advantage of the binuclear molecular geometry in order to suppress dopant intermolecular interactions. No evidence of low‐energy emission from aggregate states is observed in OLEDs made with 50 % 1 doped into mCP. OLEDs made using 100 % 1 as an emissive layer display red luminescence, which is believed to originate from distorted complexes with compressed Pt–Pt separations located in defect sites within the neat film. White OLEDs are fabricated using 1 and 3 in three different device architectures, either with one or two dopants in dual emissive layers or both dopants in a single emissive layer. All the white OLEDs have high quantum efficiency (~ 5 %) and brightness (~ 600 Cd m–2 at 10 V).  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