全文获取类型
收费全文 | 551445篇 |
免费 | 7159篇 |
国内免费 | 1584篇 |
专业分类
电工技术 | 10603篇 |
综合类 | 1490篇 |
化学工业 | 80330篇 |
金属工艺 | 19160篇 |
机械仪表 | 16344篇 |
建筑科学 | 13662篇 |
矿业工程 | 2218篇 |
能源动力 | 14073篇 |
轻工业 | 49011篇 |
水利工程 | 5176篇 |
石油天然气 | 7081篇 |
武器工业 | 79篇 |
无线电 | 67682篇 |
一般工业技术 | 100706篇 |
冶金工业 | 111595篇 |
原子能技术 | 9794篇 |
自动化技术 | 51184篇 |
出版年
2021年 | 4045篇 |
2019年 | 3838篇 |
2018年 | 6856篇 |
2017年 | 6980篇 |
2016年 | 7659篇 |
2015年 | 5218篇 |
2014年 | 8093篇 |
2013年 | 23789篇 |
2012年 | 14401篇 |
2011年 | 19463篇 |
2010年 | 14140篇 |
2009年 | 16198篇 |
2008年 | 17060篇 |
2007年 | 16845篇 |
2006年 | 15257篇 |
2005年 | 16517篇 |
2004年 | 15487篇 |
2003年 | 14733篇 |
2002年 | 13149篇 |
2001年 | 13155篇 |
2000年 | 12214篇 |
1999年 | 12881篇 |
1998年 | 33482篇 |
1997年 | 23766篇 |
1996年 | 18439篇 |
1995年 | 14019篇 |
1994年 | 12404篇 |
1993年 | 12094篇 |
1992年 | 8909篇 |
1991年 | 8469篇 |
1990年 | 8286篇 |
1989年 | 7854篇 |
1988年 | 7647篇 |
1987年 | 6523篇 |
1986年 | 6508篇 |
1985年 | 7652篇 |
1984年 | 6961篇 |
1983年 | 6445篇 |
1982年 | 5929篇 |
1981年 | 6230篇 |
1980年 | 5792篇 |
1979年 | 5522篇 |
1978年 | 5282篇 |
1977年 | 6658篇 |
1976年 | 8882篇 |
1975年 | 4742篇 |
1974年 | 4519篇 |
1973年 | 4575篇 |
1972年 | 3719篇 |
1971年 | 3408篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
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
62.
63.
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
64.
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
65.
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
66.
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
67.
Many organisations use decision models in their processes such as tables or trees to provide decision support to their operational
divisions. For example, in fault management, customer contact centre operators usually use a decision model in the form of
prescribed interviews. Based on the answers given by customers, the operator navigates through the decision model to reach
an assessment of the problem. In order to achieve customer satisfaction and operational excellence, it is very important to
constantly monitor the performance of a decision model not only on an overall level, but also on the level of individual decisions.
In this paper we present a configurable business process analytics tool, known as the intelligent Universal Service Management
System, that constantly monitors decision data and is capable of optimising the decisions based on high-level business objectives.
We explain the various features of the software and show how it can be used to optimise decision processes. We also show how
we can easily provide a customised version to monitor the performance of provision processes. 相似文献
68.
69.
Sébastien Ambellouis Fran?ois Cabestaing Jack-Gérard Postaire 《IEEE transactions on image processing》2006,15(6):1601-1609
Energy-based methods for motion estimation in image sequences process the input data either in the spatiotemporal or in the frequency domain. In both cases, the algorithms already described in the literature often require a huge number of elementary operations. In this paper, we describe a class of velocity selective filters which yield an accurate detection of the edges moving in the sequence. We first present a filtering scheme based on a convolution operation computed on a finite size neighborhood and describe its properties in the spatiotemporal and frequency domains. Then, we show that filters with similar properties can be implemented recursively, i.e., as convolutions computed on infinite-size neighborhoods. As an example, we finally show the filters' responses in the case of two superimposed translational motions. 相似文献
70.
M. N. Levin A. V. Tatarintsev V. A. Makarenko V. R. Gitlin 《Russian Microelectronics》2006,35(5):329-336
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