全文获取类型
收费全文 | 982992篇 |
免费 | 12032篇 |
国内免费 | 2496篇 |
专业分类
电工技术 | 17195篇 |
综合类 | 3092篇 |
化学工业 | 148576篇 |
金属工艺 | 39535篇 |
机械仪表 | 30367篇 |
建筑科学 | 23509篇 |
矿业工程 | 6066篇 |
能源动力 | 24722篇 |
轻工业 | 79014篇 |
水利工程 | 11216篇 |
石油天然气 | 19442篇 |
武器工业 | 64篇 |
无线电 | 107851篇 |
一般工业技术 | 192623篇 |
冶金工业 | 173565篇 |
原子能技术 | 20207篇 |
自动化技术 | 100476篇 |
出版年
2021年 | 8344篇 |
2020年 | 6148篇 |
2019年 | 7878篇 |
2018年 | 26396篇 |
2017年 | 25403篇 |
2016年 | 23207篇 |
2015年 | 9903篇 |
2014年 | 15768篇 |
2013年 | 41619篇 |
2012年 | 27085篇 |
2011年 | 41687篇 |
2010年 | 33878篇 |
2009年 | 34626篇 |
2008年 | 36322篇 |
2007年 | 36758篇 |
2006年 | 26143篇 |
2005年 | 24762篇 |
2004年 | 23672篇 |
2003年 | 23401篇 |
2002年 | 21918篇 |
2001年 | 21220篇 |
2000年 | 20122篇 |
1999年 | 20607篇 |
1998年 | 51179篇 |
1997年 | 36455篇 |
1996年 | 28185篇 |
1995年 | 21292篇 |
1994年 | 18867篇 |
1993年 | 18486篇 |
1992年 | 13715篇 |
1991年 | 13008篇 |
1990年 | 12866篇 |
1989年 | 12455篇 |
1988年 | 11833篇 |
1987年 | 10630篇 |
1986年 | 10379篇 |
1985年 | 11682篇 |
1984年 | 10677篇 |
1983年 | 9910篇 |
1982年 | 9137篇 |
1981年 | 9274篇 |
1980年 | 8839篇 |
1979年 | 8783篇 |
1978年 | 8587篇 |
1977年 | 9909篇 |
1976年 | 12844篇 |
1975年 | 7583篇 |
1974年 | 7214篇 |
1973年 | 7369篇 |
1972年 | 6170篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
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
82.
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.
87.
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
88.
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
89.
Stewart C. Kai Shen Dwarkadas S. Scott M.L. Jian Yin 《Distributed Systems Online, IEEE》2004,5(10):1-1
The growth of the Internet and of various intranets has spawned a wealth of online services, most of which are implemented on local-area clusters using remote invocation (for example, remote procedure call/remote method invocation) among manually placed application components. Component placement can be a significant challenge for large-scale services, particularly when application resource needs are workload dependent. Automatic component placement has the potential to maximize overall system throughput. The key idea is to construct (offline) a mapping between input workload and individual-component resource consumption. Such mappings, called component profiles, then support high-performance placement. Preliminary results on an online auction benchmark based on J2EE (Java 2 Platform, Enterprise Edition) suggest that profile-driven tools can identify placements that achieve near-optimal overall throughput. 相似文献
90.
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