全文获取类型
收费全文 | 3092篇 |
免费 | 328篇 |
国内免费 | 84篇 |
专业分类
电工技术 | 666篇 |
技术理论 | 1篇 |
综合类 | 253篇 |
化学工业 | 651篇 |
金属工艺 | 27篇 |
机械仪表 | 70篇 |
建筑科学 | 211篇 |
矿业工程 | 65篇 |
能源动力 | 208篇 |
轻工业 | 142篇 |
水利工程 | 46篇 |
石油天然气 | 65篇 |
武器工业 | 10篇 |
无线电 | 104篇 |
一般工业技术 | 241篇 |
冶金工业 | 381篇 |
原子能技术 | 18篇 |
自动化技术 | 345篇 |
出版年
2024年 | 9篇 |
2023年 | 45篇 |
2022年 | 70篇 |
2021年 | 99篇 |
2020年 | 119篇 |
2019年 | 88篇 |
2018年 | 95篇 |
2017年 | 102篇 |
2016年 | 133篇 |
2015年 | 151篇 |
2014年 | 213篇 |
2013年 | 190篇 |
2012年 | 203篇 |
2011年 | 259篇 |
2010年 | 177篇 |
2009年 | 174篇 |
2008年 | 140篇 |
2007年 | 149篇 |
2006年 | 167篇 |
2005年 | 125篇 |
2004年 | 107篇 |
2003年 | 90篇 |
2002年 | 94篇 |
2001年 | 70篇 |
2000年 | 46篇 |
1999年 | 41篇 |
1998年 | 42篇 |
1997年 | 30篇 |
1996年 | 31篇 |
1995年 | 24篇 |
1994年 | 25篇 |
1993年 | 12篇 |
1992年 | 12篇 |
1991年 | 11篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 10篇 |
1986年 | 8篇 |
1984年 | 13篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1966年 | 6篇 |
1965年 | 8篇 |
1964年 | 12篇 |
1962年 | 5篇 |
1961年 | 8篇 |
1959年 | 6篇 |
1958年 | 6篇 |
1957年 | 8篇 |
1955年 | 8篇 |
排序方式: 共有3504条查询结果,搜索用时 171 毫秒
11.
Stereotype threat research has demonstrated that stereotypes can harm student performance in the face of public evaluation by peers or an experimenter. The current study examined whether stereotypes can also threaten in private settings. Female students completed a math test in 3-person groups, which consisted of either 2 other women (same gender) or 2 men (minority). In addition, students either believed their performance would be broadcasted to their peers (public) or not (private). Results revealed that minority students performed worse than same-gender students in both public and private environments. This finding supports the concept of threatening intellectual environments and shows how far reaching the effects of stereotypes can be. The authors discuss these findings in relation to research on tokenism and to stereotype threat and its educational implications. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
12.
Controllability of One Spin and Two Interacting Spins 总被引:1,自引:0,他引:1
Mathematics of Control, Signals, and Systems - ?We consider the problem of steering control for the systems of one spin ½ particle and two interacting spin ½ particles in an... 相似文献
13.
This article argues that an iconic event in the history of helping research--the story of the 38 witnesses who remained inactive during the murder of Kitty Genovese--is not supported by the available evidence. Using archive material, the authors show that there is no evidence for the presence of 38 witnesses, or that witnesses observed the murder, or that witnesses remained inactive. Drawing a distinction between the robust bystander research tradition and the story of the 38 witnesses, the authors explore the consequences of the story for the discipline of psychology. They argue that the story itself plays a key role in psychology textbooks. They also suggest that the story marks a new way of conceptualizing the dangers of immersion in social groups. Finally, they suggest that the story itself has become a modern parable, the telling of which has served to limit the scope of inquiry into emergency helping. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
14.
Peter Fleischmann Ingo Janiszczak 《Applicable Algebra in Engineering, Communication and Computing》1996,7(3):221-234
In this paper an algorithm is presented to determine the number of semisimple conjugacy classes for a given centralizertype for the Chevalley groupsSL
n(q) andSU
n(q). Moreover we give the exact number of regular semisimple classes of this groups and a summary of results on the generic classnumber of exceptional Chevalley groups of adjoint type.The first author acknowledges financial support by a grant of the Deutsche Forschungsgemeinschaft 相似文献
15.
The nature of the interaction of monomer, and the early stages of growth of oligomers of ethylene on a rather more uniform surface of Cr/SiO2 catalyst than hitherto studied has been investigated by differenceFTIR spectroscopy using C2D4 and C2H4 as reactants both with and without subsequent treatment of the catalyst with CO andTHF. The active catalyst was prepared by reaction of vapour phase CrO2Cl2 with the vicinal hydroxyls of the silica surface. Three distinct kinds of methylene groups were detected. Arguments are given for assigning the peaks at 2935 and 2860 cm–1 to CH2 groups directly bound to the active site and those at 2920 and 2850 to CH2s in the growing chain well removed from the Cr. The peaks at 2160 and 2165 cm–1 are attributed to CD2 groups hydrogen bonded to surface hydroxyls. 相似文献
16.
Preacher Kristopher J.; Rucker Derek D.; MacCallum Robert C.; Nicewander W. Alan 《Canadian Metallurgical Quarterly》2005,10(2):178
Analysis of continuous variables sometimes proceeds by selecting individuals on the basis of extreme scores of a sample distribution and submitting only those extreme scores to further analysis. This sampling method is known as the extreme groups approach (EGA). EGA is often used to achieve greater statistical power in subsequent hypothesis tests. However, there are several largely unrecognized costs associated with EGA that must be considered. The authors illustrate the effects EGA can have on power, standardized effect size, reliability, model specification, and the interpretability of results. Finally, the authors discuss alternative procedures, as well as possible legitimate uses of EGA. The authors urge researchers, editors, reviewers, and consumers to carefully assess the extent to which EGA is an appropriate tool in their own research and in that of others. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
17.
Hua-Chieh Li 《Applicable Algebra in Engineering, Communication and Computing》2007,18(4):313-348
In this paper, we give a general criterion to determine when a complex space-time block code has a ring structure and then
we provide a complete list of complex space-time block codes which have ring structures up to size 4. 相似文献
18.
Much research has examined gender and age effects on compensation, concluding that a wage gap exists favoring men and negative stereotypes against older workers persist. Although the effect of an employee's gender or age has been widely studied, little work has examined the impact of the demographic characteristics of a focal employee's immediate referent groups (e.g., subordinates, peers, or supervisors) on pay. The effect of the gender and age composition of a focal manager's subordinates, peers, and supervisor on the manager's compensation levels was investigated in a sample of 2,178 managers across a wide range of organizations and functional areas. After controlling for a number of human capital variables, results indicated that not only does a wage gap favoring men exist, but also managerial pay is lower when managers' referent groups are largely female, when subordinates are outside the prime age group, and when peers and supervisors are younger. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
19.
Yoon Carolyn; Feinberg Fred; Hu Ping; Gutchess Angela Hall; Hedden Trey; Chen Hiu-Ying Mary; Jing Qicheng; Cui Yao; Park Denise C. 《Canadian Metallurgical Quarterly》2004,19(3):379
Understanding how aging influences cognition across different cultures has been hindered by a lack of standardized, cross-referenced verbal stimuli. This study introduces a database of such item-level stimuli for both younger and older adults, in China and the United States, and makes 3 distinct contributions. First, the authors specify which item categories generalize across age and/or cultural groups, rigorously quantifying differences among them. Second, they introduce novel, powerful methods to measure between-group differences in freely generated ranked data, the rank-ordered logit model and Hellinger Affinity. Finally, a broad archive of tested, cross-linguistic stimuli is now freely available to researchers: data, similarity measures, and all stimulus materials for 105 categories and 4 culture-by-age groups, comprising over 10,000 fully translated unique item responses. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
20.
The fractions obtained from bagasse after activation with 17.5% NaOH, alternative alkylation with quarternary ammonium groups and extraction with 80% ethanol, water and 5% NaOH, were analyzed using pyrolysis-field ionization mass spectrometry (Py-FIMS). The proposed degradation products from lignin were mostly symmetric fragments containing two aromatic rings while the compounds formed from polysaccharides were the result of dehydration reactions. From the temperature-resolved Py-FIMS it could be seen that ethanol-lignin starts to degrade at temperatures lower than 180°C before the degradation of the hemicellulose fraction. The lignin markers are eliminated from hemicellulose fractions before the polysaccharide gasification starts. The quarternary ammonium groups are cleaved from the fractions at temperatures lower than 200°C. 相似文献