全文获取类型
收费全文 | 39426篇 |
免费 | 1337篇 |
国内免费 | 64篇 |
专业分类
电工技术 | 408篇 |
综合类 | 30篇 |
化学工业 | 7562篇 |
金属工艺 | 942篇 |
机械仪表 | 799篇 |
建筑科学 | 2046篇 |
矿业工程 | 198篇 |
能源动力 | 1126篇 |
轻工业 | 3089篇 |
水利工程 | 450篇 |
石油天然气 | 120篇 |
武器工业 | 5篇 |
无线电 | 2760篇 |
一般工业技术 | 6523篇 |
冶金工业 | 7587篇 |
原子能技术 | 302篇 |
自动化技术 | 6880篇 |
出版年
2023年 | 223篇 |
2022年 | 462篇 |
2021年 | 721篇 |
2020年 | 483篇 |
2019年 | 647篇 |
2018年 | 807篇 |
2017年 | 723篇 |
2016年 | 869篇 |
2015年 | 779篇 |
2014年 | 1086篇 |
2013年 | 2520篇 |
2012年 | 1744篇 |
2011年 | 2189篇 |
2010年 | 1737篇 |
2009年 | 1641篇 |
2008年 | 1884篇 |
2007年 | 1873篇 |
2006年 | 1693篇 |
2005年 | 1503篇 |
2004年 | 1241篇 |
2003年 | 1186篇 |
2002年 | 1107篇 |
2001年 | 758篇 |
2000年 | 616篇 |
1999年 | 650篇 |
1998年 | 861篇 |
1997年 | 742篇 |
1996年 | 687篇 |
1995年 | 650篇 |
1994年 | 599篇 |
1993年 | 610篇 |
1992年 | 543篇 |
1991年 | 329篇 |
1990年 | 450篇 |
1989年 | 430篇 |
1988年 | 344篇 |
1987年 | 386篇 |
1986年 | 346篇 |
1985年 | 451篇 |
1984年 | 446篇 |
1983年 | 345篇 |
1982年 | 323篇 |
1981年 | 313篇 |
1980年 | 299篇 |
1979年 | 295篇 |
1978年 | 274篇 |
1977年 | 284篇 |
1976年 | 278篇 |
1975年 | 217篇 |
1974年 | 201篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
Dense samples of the higher boride YB22C2N have been fabricated through the spark plasma sintering (SPS) method with different sintering aids. YB22C2N is a representative of a series of newly discovered rare-earth borocarbonitrides, which may be the long-awaited n-type counterpart of boron carbide, “B4C.” The effect of Si, SiC, Al, and TiC additions on the sintering process of YB22C2N has been studied. The best sintered bodies with densities higher than 90% of theoretical density were obtained by means of SPS at 1700°C. We show that the additive choice and pressure have an effect on grain size and density. An investigation of the effect of atmosphere on the sintering behavior has also been carried out. It was found that sinterability is enhanced under nitrogen atmosphere. Thermoelectric properties of the materials sintered with additives have been evaluated, and we discuss their dependences on the fabrication process route. 相似文献
912.
913.
David Nicolas Hopmann Claes H. de Vreese Erik Albæk 《The Journal of communication》2011,61(2):264-282
This article investigates the determinants of the incumbency bonuses in news coverage. Two main factors are identified: the distribution of political power and changes in the media market. To test these assumptions, a content analysis of the news coverage of 5 national election campaigns in Denmark was conducted (4,592 news stories). First, the more unevenly political power is distributed, the more visible the government is. Second, results suggest a trade‐off between the incumbency bonus and the coverage of nonsubstantive issues. Third, changes in news coverage seem to be more driven by changes in the political system than by changes in the media market. Finally, it is discussed how future research can further our understanding of political imbalances in news coverage. 相似文献
914.
State-of-the-art devices in the consumer electronics market are relying more and more on Multi-Processor Systems-On-Chip (MPSoCs) as an efficient solution to meet their multiple design constrains, such as low cost, low power consumption, high performance and short time-to-market. In fact, as technology scales down, logic density and power density increase, generating hot spots that seriously affect the MPSoC performance and can physically damage the final system behavior. Moreover, forthcoming three-dimensional (3D) MPSoCs can achieve higher system integration density, but the aforementioned thermal problems are seriously aggravated. Thus, new thermal exploration tools are needed to study the temperature variation effects inside 3D MPSoCs. In this paper, we present a novel approach for fast transient thermal modeling and analysis of 3D MPSoCs with active (liquid) cooling solutions, while capturing the hardware-software interaction. In order to preserve both accuracy and speed, we propose a close-loop framework that combines the use of Field Programmable Gate Arrays (FPGAs) to emulate the hardware components of 2D/3D MPSoC platforms with a highly optimized thermal simulator, which uses an RC-based linear thermal model to analyze the liquid flow. The proposed framework offers speed-ups of more than three orders of magnitude when compared to cycle-accurate 3D MPSoC thermal simulators. Thus, this approach enables MPSoC designers to validate different hardware- and software-based 3D thermal management policies in real-time, and while running real-life applications, including liquid cooling injection control. 相似文献
915.
916.
917.
Baucom Brian R.; Atkins David C.; Eldridge Kathleen; McFarland Pamela; Sevier Mia; Christensen Andrew 《Canadian Metallurgical Quarterly》2011,25(4):570
Associations between vocally expressed emotional arousal, influence tactics, and demand/withdraw behavior were examined in a treatment-seeking sample of 130 seriously and stably distressed, married, heterosexual couples and in a community sample (N = 38) of 18 married heterosexual and 20 dating heterosexual couples. Fundamental frequency was used to measure emotional arousal, and computational linguistics were used to measure influence tactics. Higher levels of demand/withdraw behavior were associated with greater use of manipulative and controlling influence tactics, higher levels of emotional arousal, and less frequent use of cooperative and compromising influence tactics. Overall, demanders tended to express more arousal and to use more influence tactics than withdrawers. Both influence tactics and emotional arousal were uniquely associated with demand/withdraw behavior. Implications of results are discussed for refining theories of demand/withdraw interaction. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
918.
Aguayo David; Herman Keith; Ojeda Lizette; Flores Lisa Y. 《Canadian Metallurgical Quarterly》2011,4(2):79
In hopes of promoting college success among Mexican Americans, researchers have identified factors related to their academic performance. A gap in the literature exists between the interactive role of acculturation, enculturation, and generation status in predicting college self-efficacy and college performance (grade-point average, or GPA). To fill this void, this study investigated the relation of demographic variables (e.g., age, gender, socioeconomic status) and cultural variables (e.g., acculturation, enculturation, generation status) on academic outcomes (e.g., college self-efficacy, college performance) among 408 Mexican-American college students. Results of a series of hierarchical regression analyses indicated socioeconomic status, generation status, enculturation, and acculturation had significant positive effects on college self-efficacy; socioeconomic status and the interaction of higher enculturation and first-generation status were positively and significantly related to GPA. Post-hoc analyses indicated college self-efficacy predicted college performance for students who were second generation and beyond. Implications for research and practice are discussed. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
919.
A great deal of developmental research has relied on self-reports solicited using the “some/other” question format (“Some students think that… but other students think that…”). This article reports tests of the assumptions underlying its use: that it conveys to adolescents that socially undesirable attitudes, beliefs, or behaviors are not uncommon and legitimizes reporting them, yielding more valid self-reports than would be obtained by “direct” questions, which do not mention what other people think or do. A meta-analysis of 11 experiments embedded in four surveys of diverse samples of adolescents did not support the assumption that the some/other form increases validity. Although the some/other form led adolescents to think that undesirable attitudes, beliefs, or behaviors were more common and resulted in more reports of those attitudes and behaviors, answers to some/other questions were lower in criterion validity than were answers to direct questions. Because some/other questions take longer to ask and answer and require greater cognitive effort from participants (because they involve more words), and because they decrease measurement accuracy, the some/other question format seems best avoided. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
920.
Degeneffe Charles Edmund; Chan Fong; Dunlap Laura; Man David; Sung Connie 《Canadian Metallurgical Quarterly》2011,56(3):243
Objective: To use multitrait analysis to determine the measurement structure of the Caregiver Empowerment Scale (CES). Participants: An American sample of 87 adult primary family caregivers of persons with traumatic brain injury (TBI). Results: A four-factor structure was identified including factor 1 (Advocacy Self-Efficacy), factor 2 (Community Self-Efficacy), factor 3 (Caregiver Self-Efficacy), and factor 4 (Personal Self-Efficacy). Conclusions: The CES provides clinicians and researchers a means to assess self-perceived coping abilities of family caregivers of persons with TBI. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献