全文获取类型
收费全文 | 1752篇 |
免费 | 99篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 9篇 |
综合类 | 6篇 |
化学工业 | 318篇 |
金属工艺 | 25篇 |
机械仪表 | 25篇 |
建筑科学 | 43篇 |
矿业工程 | 2篇 |
能源动力 | 60篇 |
轻工业 | 115篇 |
水利工程 | 30篇 |
石油天然气 | 1篇 |
无线电 | 217篇 |
一般工业技术 | 406篇 |
冶金工业 | 349篇 |
原子能技术 | 5篇 |
自动化技术 | 242篇 |
出版年
2023年 | 22篇 |
2022年 | 12篇 |
2021年 | 36篇 |
2020年 | 36篇 |
2019年 | 57篇 |
2018年 | 52篇 |
2017年 | 52篇 |
2016年 | 57篇 |
2015年 | 45篇 |
2014年 | 64篇 |
2013年 | 100篇 |
2012年 | 96篇 |
2011年 | 130篇 |
2010年 | 91篇 |
2009年 | 92篇 |
2008年 | 84篇 |
2007年 | 77篇 |
2006年 | 63篇 |
2005年 | 63篇 |
2004年 | 58篇 |
2003年 | 27篇 |
2002年 | 33篇 |
2001年 | 24篇 |
2000年 | 19篇 |
1999年 | 19篇 |
1998年 | 38篇 |
1997年 | 37篇 |
1996年 | 24篇 |
1995年 | 23篇 |
1994年 | 22篇 |
1993年 | 34篇 |
1992年 | 18篇 |
1991年 | 14篇 |
1990年 | 11篇 |
1989年 | 13篇 |
1988年 | 10篇 |
1987年 | 12篇 |
1986年 | 7篇 |
1985年 | 14篇 |
1984年 | 14篇 |
1983年 | 10篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 16篇 |
1978年 | 13篇 |
1977年 | 13篇 |
1976年 | 13篇 |
1975年 | 10篇 |
1964年 | 9篇 |
排序方式: 共有1853条查询结果,搜索用时 31 毫秒
151.
Longitudinal stability of temperamental exuberance and social–emotional outcomes in early childhood.
Degnan Kathryn A.; Hane Amie Ashley; Henderson Heather A.; Moas Olga Lydia; Reeb-Sutherland Bethany C.; Fox Nathan A. 《Canadian Metallurgical Quarterly》2011,47(3):765
The goals of the current study were to investigate the stability of temperamental exuberance across infancy and toddlerhood and to examine the associations between exuberance and social–emotional outcomes in early childhood. The sample consisted of 291 4-month-olds followed at 9, 24, and 36 months and again at 5 years of age. Behavioral measures of exuberance were collected at 9, 24, and 36 months. At 36 months, frontal electroencephalogram (EEG) asymmetry was assessed. At 5 years, maternal reports of temperament and behavior problems were collected, as were observational measures of social behavior during an interaction with an unfamiliar peer in the laboratory. Latent profile analysis revealed a high, stable exuberance profile that was associated with greater ratings of 5-year externalizing behavior and surgency, as well as observed disruptive behavior and social competence with unfamiliar peers. These associations were particularly true for children who displayed left frontal EEG asymmetry. Multiple factors supported an approach bias for exuberant temperament but did not differentiate between adaptive and maladaptive social–emotional outcomes at 5 years of age. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
152.
Energy consumption in China is expected to double over the next 20 years. Addressing the enormous scale of China's energy need and attendant increases in greenhouse gas emissions requires dramatic and rapid rollout of renewable energy technologies. Mongolia has some of the world's best renewable energy resources but the scale of its market cannot tap them efficiently. Developing Mongolia into a significant exporter of renewable energy to China will create synergies of scale moving both countries towards their energy goals, creating jobs, and fostering growth while significantly reducing GHG emissions in the region. 相似文献
153.
Valentina E. Smirnova Iosif V. Gofman Vladimir E. Yudin Irina P. Dobrovolskaya Alexander N. Shumakov Andrey L. Didenko Valentine M. Svetlichnyi Ellen Wachtel Rinat Shechter Hannah Harel Gad Marom 《Polymer Engineering and Science》2009,49(2):217-222
The solid state crystallization in drawn thermoplastic polyimide films is studied as a function of draw ratio (DR) under the effect of vapor grown carbon fiber nanoinclusions. The nucleating effect of the nanoinclusions coupled with the orientation effect of drawing generates a unique orientated layered lamellar structure, characteristic of smectic‐like mesophase. The degree of draw induced orientated crystallization increases with the content of nanoinclusions and with the DR, and is reflected in the mechanical behavior of the film. Generally, the Young's modulus and the yield point of the drawn crystalline films in the drawing direction are significantly higher compared with the noncrystalline counterparts. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers 相似文献
154.
155.
In 1991, the Fort Sheridan Army Garrison was slated for closure and remediation. This would have a significant economic and environmental impact on the region, particularly the three surrounding communities. Once the base closed, there would be about 700 acres of what are considered some of Illinois' most valuable real estate available for future use. This study identified the hazards, such as soil and groundwater contaminated with toxic or hazardous fuels, that were found as a result of the military activity; it analyzes the process by which the conflicting regulatory authorities assessed the facility. Particular emphasis focuses on how the Army communicated the risks found at the base to the three surrounding communities. 相似文献
156.
Jordan M. Anderson Jigna Patel Ajay S. Karakoti Nathan Greeneltch Diego J. Díaz Sudipta Seal 《Electrochimica acta》2011,56(5):2541
Nanocrystalline Pt/CeO2 composite electrodes were fabricated to study the electrochemical oxidation of methanol and ethanol. The performance of the electrodes was tested as the ceria solutions aged over time. It was observed that the performance oscillated with time, suggesting that the catalytic behavior towards alcohol oxidation was greatly dependent on the aging of the particles. These results point to a great dependence of the catalytic effect on the redox state of the ceria particles. 相似文献
157.
Enhancement of the oxygen gas barrier properties of polyethylene terephthalate (PET), used in the packaging industry, is the main objective here. For this purpose, nanocomposites of PET containing graphite nanoplatelets (GNPs) were prepared by melt compounding. The effects of the nanocomposites' structural morphology on oxygen gas permeability were analyzed using a range of thermal, microscopic, and mechanical characterization techniques. The investigated nanocomposite films exhibited GNP exfoliated morphology and good mixing with PET, as well as uniform dispersion within the polymer. All nanocomposite films were shown to possess superior oxygen barrier properties and improved thermal and dimensional stability compared with the plain PET films. In the best case, for 1.5 wt % GNP, the oxygen permeation was reduced by more than 99%. The improved barrier properties are attributed to the direct effect of the GNPs and to their induced increase of degree of crystallinity. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 相似文献
158.
In Internet-based commerce, sellers often use multiple distribution channels for the sale of standard consumer goods. We study a model of second-degree price discrimination in which a monopolist sells to risk-averse buyers. The seller uses two channels that differ in their risk attributes. In one channel prices and qualities are fixed and availability is assured. In the second channel, the seller offers a joint distribution of prices and qualities and may not guarantee availability. We characterize optimal two-channel selling policies. We show that it can be optimal to offer multiple identical items in a random sale event. However, the seller cannot benefit by offering two distinct quality levels in a sale event that is held with probability smaller than one. We use the model to offer explanations for the observed behavior of online sellers and discuss implementation issues in recent e-commerce environments. 相似文献
159.
This study proposed and tested a theoretical factor structure for the Alcohol Expectancy Questionnaire (AEQ; S. A. Brown, M. S. Goldman, A. Inn, & L. R. Anderson [see record 1981-01217-001]). Factors were hypothesized to (a) reflect either positive or negative reinforcement, and (b) target either personal feelings or social contexts, resulting in 4 hypothesized factors (Social Enhancement, Social Coping, Personal Enhancement, Personal Coping). Participants were 180 male and 226 female undergraduates who completed the AEQ and additional self-report measures. Confirmatory factor analysis revealed that the hypothesized model fit the data. Post hoc adjustments further improved the model. Finally, a higher order factor model fit the data best. Factors correlated in hypothesized ways with other measures: (a) Only Personal Coping expectancies correlated with negative affect; (b) self-efficacy to resist drinking for emotional relief correlated highest with Personal Coping; and (c) self-efficacy to resist social pressure to drink correlated highest with Social Enhancement. Correlations with B. C. Leigh and A. W. Stacy's (see record 1993-35856-001) Drinking Expectancy Questionnaire indicated congruent and divergent validity. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
160.
Cohen Dale J.; Ferrell Jennifer M.; Johnson Nathan 《Canadian Metallurgical Quarterly》2002,131(3):424
This article presents a theoretical and experimental framework for assessing the biases associated with the interpretation of numbers. This framework consists of having participants convert between different representations of quantities. These representations should include both variations in numerical labels that symbolize quantities and variations in displays in which quantity is inherent. Five experiments assessed how people convert between relative frequencies, decimals, and displays of dots that denote very low proportions (i.e., proportions below 1%). The participants demonstrated perceptual, response, and numerical transformation biases. Furthermore, the data suggest that relative frequencies and decimals are associated with different abstract representations of amount. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献