全文获取类型
收费全文 | 444870篇 |
免费 | 4413篇 |
国内免费 | 648篇 |
专业分类
电工技术 | 7551篇 |
综合类 | 340篇 |
化学工业 | 71967篇 |
金属工艺 | 21667篇 |
机械仪表 | 15353篇 |
建筑科学 | 9034篇 |
矿业工程 | 4519篇 |
能源动力 | 8484篇 |
轻工业 | 32628篇 |
水利工程 | 6032篇 |
石油天然气 | 15372篇 |
武器工业 | 55篇 |
无线电 | 41078篇 |
一般工业技术 | 96701篇 |
冶金工业 | 71737篇 |
原子能技术 | 14687篇 |
自动化技术 | 32726篇 |
出版年
2021年 | 4239篇 |
2019年 | 4089篇 |
2018年 | 7532篇 |
2017年 | 7776篇 |
2016年 | 8226篇 |
2015年 | 4636篇 |
2014年 | 8060篇 |
2013年 | 18399篇 |
2012年 | 11955篇 |
2011年 | 15420篇 |
2010年 | 12392篇 |
2009年 | 13729篇 |
2008年 | 14237篇 |
2007年 | 14093篇 |
2006年 | 11962篇 |
2005年 | 10489篇 |
2004年 | 10241篇 |
2003年 | 9916篇 |
2002年 | 9908篇 |
2001年 | 9625篇 |
2000年 | 9442篇 |
1999年 | 8853篇 |
1998年 | 18663篇 |
1997年 | 13815篇 |
1996年 | 10629篇 |
1995年 | 8472篇 |
1994年 | 7705篇 |
1993年 | 7718篇 |
1992年 | 6379篇 |
1991年 | 6194篇 |
1990年 | 6452篇 |
1989年 | 6261篇 |
1988年 | 6018篇 |
1987年 | 5631篇 |
1986年 | 5583篇 |
1985年 | 6138篇 |
1984年 | 5927篇 |
1983年 | 5565篇 |
1982年 | 5251篇 |
1981年 | 5347篇 |
1980年 | 5274篇 |
1979年 | 5381篇 |
1978年 | 5569篇 |
1977年 | 5881篇 |
1976年 | 7093篇 |
1975年 | 5031篇 |
1974年 | 5038篇 |
1973年 | 5153篇 |
1972年 | 4495篇 |
1971年 | 4143篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
为了分析多水库系统中两座水库之间灌溉用水的分配问题,建立了基到动态规划的神经网络模型。为了研究从一座上游水库取水在下游两座之库之间进行水量分配的问题,提出了3个状态变量和4个决策变量的改进的动态规划算法。采用神经网络模型,用3个状态变量动态规划算法得出调度原则,就所研究的多水库系统实例来说,新的动态规划神经网络模型的性能很好,将该模型的性能与临时凑合的标准调度原则和以前推荐使用的约束动态规划神经网络模型进行了比较。 相似文献
172.
173.
G. I. Glazov A. M. Garaiev R. V. Timerkhanov 《Chemistry and Technology of Fuels and Oils》2003,39(1-2):26-53
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
174.
Reducible rank codes and their applications to cryptography 总被引:2,自引:0,他引:2
Gabidulin E.M. Ourivski A.V. Honary B. Ammar B. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2003,49(12):3289-3293
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
175.
By exploiting a general cyclostationary (CS) statistics-based framework, this letter develops a rigorous and unified asymptotic (large sample) performance analysis setup for a class of blind feedforward timing epoch estimators for linear modulations transmitted through time nonselective flat-fading channels. Within the proposed CS framework, it is shown that several estimators proposed in the literature can be asymptotically interpreted as maximum likelihood (ML) estimators applied on a (sub)set of the second- (and/or higher) order statistics of the received signal. The asymptotic variance of these ML estimators is established in closed-form expression and compared with the modified Crame/spl acute/r-Rao bound. It is shown that the timing estimator proposed by Oerder and Meyr achieves asymptotically the best performance in the class of estimators which exploit all the second-order statistics of the received signal, and its performance is insensitive to oversampling rates P as long as P/spl ges/3. Further, an asymptotically best consistent estimator, which achieves the lowest asymptotic variance among all the possible estimators that can be derived by exploiting jointly the second- and fourth-order statistics of the received signal, is also proposed. 相似文献
176.
B. Ma P.I. Djurovich S. Garon B. Alleyne M.E. Thompson 《Advanced functional materials》2006,16(18):2438-2446
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 C∧NPt(μ‐pz)2PtC∧N (where C∧N = 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
177.
The aim of this study was to evaluate the use of total coliforms (TC) and faecal coliforms (FC) using a membrane filtration method for precise monitoring of faecal pollution in Korean surface water. The samples were collected in Korea from both main rivers and their tributaries. Presumptive TC * FC were enumerated. The ratios of presumptive FC to TC were not constant, but varied widely, and TC were difficult to enumerate because of overgrowth by background colonies. For FC this was not the case. Seven hundred and three purified strains of presumptive TC * FC and their background colonies were biotyped using API 20E. Among 272 presumptive TC, non-faecal related species, Aeromonas hydrophila dominated (34.6%) and E. coli accounted for only 5.1%. In contrast, E. coli made up 89% of the 209 presumptive FC. Furthermore, of 164 background colonies on Endo Agar LES, 54.9% was A. hydrophila, while background colonies on m-FC Agar were few (58 strains), and despite their atypical colony appearance, most of them were biotyped as enteric bacteria. These results reveal that the detection of FC rather than TC using m-FC Agar is more appropriate for faecal pollution monitoring in eutrophicated surface water located in a temperate region. 相似文献
178.
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
179.
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
180.
Removal of gold from basic solutions containing [Au(CN)2]? has been demonstrated using the inherently conducting polymer polypyrrole. Polymers containing sulfonated aromatic dopants have been found to display a significant ability to remove gold from such solutions. Experiments performed in solutions containing both gold and copper cyanide complexes indicate that the recovery process is not highly selective. However, the polypyrroles used display significantly faster rates of gold recovery than activated carbon. © 2003 Society of Chemical Industry 相似文献