全文获取类型
收费全文 | 705473篇 |
免费 | 7733篇 |
国内免费 | 1541篇 |
专业分类
电工技术 | 13379篇 |
综合类 | 558篇 |
化学工业 | 107551篇 |
金属工艺 | 28244篇 |
机械仪表 | 22099篇 |
建筑科学 | 15473篇 |
矿业工程 | 4731篇 |
能源动力 | 17785篇 |
轻工业 | 55155篇 |
水利工程 | 8051篇 |
石油天然气 | 16188篇 |
武器工业 | 45篇 |
无线电 | 79722篇 |
一般工业技术 | 141942篇 |
冶金工业 | 130258篇 |
原子能技术 | 16747篇 |
自动化技术 | 56819篇 |
出版年
2021年 | 6240篇 |
2019年 | 6030篇 |
2018年 | 10422篇 |
2017年 | 10598篇 |
2016年 | 11109篇 |
2015年 | 6978篇 |
2014年 | 11879篇 |
2013年 | 31708篇 |
2012年 | 18498篇 |
2011年 | 25090篇 |
2010年 | 20175篇 |
2009年 | 22716篇 |
2008年 | 23219篇 |
2007年 | 22971篇 |
2006年 | 20113篇 |
2005年 | 18367篇 |
2004年 | 17669篇 |
2003年 | 17249篇 |
2002年 | 16715篇 |
2001年 | 16561篇 |
2000年 | 15748篇 |
1999年 | 15990篇 |
1998年 | 39482篇 |
1997年 | 27875篇 |
1996年 | 21525篇 |
1995年 | 16368篇 |
1994年 | 14607篇 |
1993年 | 14391篇 |
1992年 | 10714篇 |
1991年 | 10424篇 |
1990年 | 10235篇 |
1989年 | 9946篇 |
1988年 | 9410篇 |
1987年 | 8321篇 |
1986年 | 8207篇 |
1985年 | 9303篇 |
1984年 | 8355篇 |
1983年 | 7882篇 |
1982年 | 7143篇 |
1981年 | 7378篇 |
1980年 | 6910篇 |
1979年 | 6917篇 |
1978年 | 6811篇 |
1977年 | 7664篇 |
1976年 | 9743篇 |
1975年 | 6069篇 |
1974年 | 5846篇 |
1973年 | 5858篇 |
1972年 | 5062篇 |
1971年 | 4661篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
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
82.
Lopera J.M. Prieto M.J. Pernia A.M. Nuno F. 《Power Electronics, IEEE Transactions on》2003,18(3):896-906
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
83.
84.
Myers Nicholas D.; Payment Craig A.; Feltz Deborah L. 《Canadian Metallurgical Quarterly》2004,8(3):182
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
85.
Halliday-Boykins Colleen A.; Henggeler Scott W.; Rowland Melisa D.; DeLucia Christian 《Canadian Metallurgical Quarterly》2004,72(6):993
The authors examined heterogeneity in symptom trajectories among youths following psychiatric crises as well as the psychosocial correlates and placement outcomes associated with identified trajectories. Using semiparametric mixture modeling with 156 youths approved for psychiatric hospitalization, the authors identified 5 trajectories based on symptoms over the 16 months following crisis: high improved, high unimproved, borderline improved, borderline unimproved, and subclinical. Membership in unimproved symptom groups was associated with less suicidality, younger age, more youth hopelessness, and more caregiver empowerment. Improved symptom group membership predicted long-term decreases in days in out-of-home placements. More important, and in contrast with general impressions from the existing literature, findings suggest that a substantive proportion of youths with serious emotional disturbance sustain high levels of symptomatology following intensive mental health services. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
86.
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
87.
Zs. T
kei D. Kelleher B. Mebarki T. Mandrekar S. Guggilla K. Maex 《Microelectronic Engineering》2003,70(2-4):358-362
Passivated single damascene copper SiO2 damascene lines were evaluated in combination with TiSiN and Ta(N)/Ta diffusion barriers. Leakage current, breakdown and time-dependent dielectric breakdown properties were investigated on a wafer level basis for temperatures ranging between room temperature and 150 °C. It is found that the leakage performance of the wafers with a TiSiN barrier is better at room temperature, but at 150 °C the performance levels out with Ta(N)/Ta. Time-dependent dielectric breakdown measurements at 150 °C show that the lifetime of the interconnect is higher with the selected Ta(N)/Ta barrier than for TiSiN. 相似文献
88.
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
89.
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
90.
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