全文获取类型
收费全文 | 4254篇 |
免费 | 204篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 41篇 |
综合类 | 4篇 |
化学工业 | 857篇 |
金属工艺 | 91篇 |
机械仪表 | 86篇 |
建筑科学 | 291篇 |
矿业工程 | 8篇 |
能源动力 | 155篇 |
轻工业 | 244篇 |
水利工程 | 60篇 |
石油天然气 | 34篇 |
武器工业 | 1篇 |
无线电 | 313篇 |
一般工业技术 | 843篇 |
冶金工业 | 665篇 |
原子能技术 | 19篇 |
自动化技术 | 756篇 |
出版年
2023年 | 45篇 |
2022年 | 78篇 |
2021年 | 133篇 |
2020年 | 86篇 |
2019年 | 110篇 |
2018年 | 112篇 |
2017年 | 92篇 |
2016年 | 124篇 |
2015年 | 99篇 |
2014年 | 142篇 |
2013年 | 301篇 |
2012年 | 246篇 |
2011年 | 318篇 |
2010年 | 219篇 |
2009年 | 206篇 |
2008年 | 229篇 |
2007年 | 208篇 |
2006年 | 182篇 |
2005年 | 128篇 |
2004年 | 106篇 |
2003年 | 119篇 |
2002年 | 99篇 |
2001年 | 71篇 |
2000年 | 57篇 |
1999年 | 56篇 |
1998年 | 70篇 |
1997年 | 65篇 |
1996年 | 52篇 |
1995年 | 40篇 |
1994年 | 59篇 |
1993年 | 41篇 |
1992年 | 39篇 |
1991年 | 29篇 |
1990年 | 40篇 |
1989年 | 34篇 |
1988年 | 33篇 |
1987年 | 40篇 |
1986年 | 17篇 |
1985年 | 28篇 |
1984年 | 24篇 |
1983年 | 26篇 |
1982年 | 27篇 |
1981年 | 16篇 |
1980年 | 16篇 |
1979年 | 27篇 |
1978年 | 24篇 |
1977年 | 21篇 |
1976年 | 16篇 |
1975年 | 17篇 |
1973年 | 13篇 |
排序方式: 共有4468条查询结果,搜索用时 46 毫秒
71.
Previous studies with macrophages that had been prelabeled with [14C]arachidonic acid (20∶4) have shown that condensed tannin is a potent agonist for the release of arachidonic acid. However,
it has not been demonstrated that the percentage release of [14C]20∶4 accurately reflects the metabolic activity of the endogenous 20∶4 pool. In order to measure the 20∶4 mass release relative
to the total cellular 20∶4 pool, the free fatty acids of freshly isolated alveolar macrophages were derivatized with a fluorescent
reagent, and then separated and quantified by high-performance liquid chromatography. The amounts of esterified fatty acids
were measured by gas chromatography of the methyl esters. Free fatty acid levels were compared to those of the total esterified
plus unesterified fatty acids to determine the actual percentage released of each fatty acid. Tannin-stimulated release of
20∶4 mass reflected that previously reported for the release of [14C]20∶4 label but at a slower rate and at a much lower percentage indicating that [14C]20∶4 had been incorporated into part of a more reactive pool. The specificity of the fatty acid release induced by tannin
and β-1,3-glucan, a known agonist for 20∶4 release, was also examined. Both agonists promoted an increase in the levels of
free 20∶4 and of other fatty acids. A comparison of the absolute increases of each of the fatty acids indicated that tannin
caused a preferential increase in the mass of free 20∶4, whereas β-1,3-glucan evoked a selective increase in the mass of 16∶0.
Deceased. 相似文献
72.
The removal of sulphur and ash from coal treated with aqueous hydrogen peroxide/sulphuric acid solutions has been studied at ambient temperature, under a variety of experimental conditions. Almost complete elimination of the sulphate and the pyritic sulphur was observed in most cases, as well as substantial reduction in the ash content. The other components of the organic coal matrix were not affected to a significant extent, indicating high selectivity of the system towards sulphur oxidation. An optimal H2SO4 concentration was established, above which the acid was found to have an adverse effect on the oxidation of pyrite by hydrogen peroxide. 相似文献
73.
During fluid catalytic cracking (FCC) operations FCC catalyst particles become contaminated with various metals. These metals impact FCC performance and currently requires equilibrium catalyst (ECAT) mixtures consisting of a blend of FCC particles with a time spent in the reactor ranging from minutes to several months to be continuously extracted and sold as low value products or sent to landfills. Here a unique method to recycle FCC ECAT particles is presented, which separates ECAT particles by metal content by synthesizing carbon nanotubes and nanofibers on the ECAT particles surface and using a biphasic system. ECAT with low metal content can be sent back to the FCC unit for further use while ECAT with high metal content can be used for other purposes. Further, we show these treated ECAT materials of high metals content will absorb oil on the surface of water and may prove useful for oil spill clean-up applications. 相似文献
74.
75.
Gordon D. Gemmell Nicholas J. Grant 《JOM Journal of the Minerals, Metals and Materials Society》1957,9(4):417-423
The effects of solid solution alloying on the creep-rupture properties, deformation characteristics, ductility, and fracture of pure aluminum were studied by means of creep-rupture tests on polished specimens of three alloys each of Al-Cu (0.24, 0.79, and 2.05 pct Cu), Al-Zn (4.93, 9.89, and 19.78 pct Zn), and Al-Mg (0.94, 1.92, and 5.10 pct Mg) at 500°, 700°, and 900°F. 相似文献
76.
Nicholas J. Grant Earl C. Roberts John Chipman 《JOM Journal of the Minerals, Metals and Materials Society》1954,6(2):145-149
An equilibrium study was made of the distribution of chromium and oxygen between liquid iron, containing less than 1 pct Cr, and simple slags of the CaO(MgO)-SiO2-FeO-Cr2O3 type in the temperature range 1526° to 1734°C The effects of slag oxidation, temperature, and basicity were observed. 相似文献
77.
Frank E. Curtis Nicholas I.M. Gould Hao Jiang Daniel P. Robinson 《Optimization methods & software》2016,31(1):157-186
In this paper, we consider augmented Lagrangian (AL) algorithms for solving large-scale nonlinear optimization problems that execute adaptive strategies for updating the penalty parameter. Our work is motivated by the recently proposed adaptive AL trust region method by Curtis et al. [An adaptive augmented Lagrangian method for large-scale constrained optimization, Math. Program. 152 (2015), pp. 201–245.]. The first focal point of this paper is a new variant of the approach that employs a line search rather than a trust region strategy, where a critical algorithmic feature for the line search strategy is the use of convexified piecewise quadratic models of the AL function for computing the search directions. We prove global convergence guarantees for our line search algorithm that are on par with those for the previously proposed trust region method. A second focal point of this paper is the practical performance of the line search and trust region algorithm variants in Matlab software, as well as that of an adaptive penalty parameter updating strategy incorporated into the Lancelot software. We test these methods on problems from the CUTEst and COPS collections, as well as on challenging test problems related to optimal power flow. Our numerical experience suggests that the adaptive algorithms outperform traditional AL methods in terms of efficiency and reliability. As with traditional AL algorithms, the adaptive methods are matrix-free and thus represent a viable option for solving large-scale problems. 相似文献
78.
Nicholas Evangelopoulos 《Information Systems Journal》2016,26(1):39-46
This study examines research published in the first 24 years of Information Systems Journal's (ISJ) publication history using a thematic space of all information systems (IS) research as the backdrop. To that end, abstracts from all contributing articles published in eight prominent IS journals in the period 1991–2014 were analysed to extract a latent semantic space of five broad research areas. A two‐dimensional projection of the results was used to create a two‐by‐two map, where one dimension represents the European vs. North American style of IS research and another dimension represents a micro vs. macro level of IS research. The ISJ is positioned in the ‘micro and European school’ quadrant. Over the course of the journal's first 24 years, research in the ISJ started with a relative focus on the IT artefact and IS development and gradually moved towards a more balanced position that includes a considerable amount of research on IT for teamwork and collaboration, as well as on IT and individuals. 相似文献
79.
Samuel Mascarenhas Nick Degens Ana Paiva Rui Prada Gert Jan Hofstede Adrie Beulens Ruth Aylett 《Autonomous Agents and Multi-Agent Systems》2016,30(5):931-962
This work addresses the challenge of creating virtual agents that are able to portray culturally appropriate behavior when interacting with other agents or humans. Because culture influences how people perceive their social reality it is important to have agent models that explicitly consider social elements, such as existing relational factors. We addressed this necessity by integrating culture into a novel model for simulating human social behavior. With this model, we operationalized a particular dimension of culture—individualism versus collectivism—within the context of an interactive narrative scenario that is part of an agent-based tool for intercultural training. Using this scenario we conducted a cross-cultural study in which participants from a collectivistic country (Portugal) were compared with participants from an individualistic country (the Netherlands) in the way they perceived and interacted with agents whose behavior was either individualistic or collectivistic, according to the configuration of the proposed model. In the obtained results, Portuguese subjects rated the collectivistic agents more positively than the Dutch but both countries had a similarly positive opinion about the individualistic agents. This experiment sheds new light on how people from different countries differ when assessing the social appropriateness of virtual agents, while also raising new research questions on this matter. 相似文献
80.