全文获取类型
收费全文 | 4684篇 |
免费 | 156篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 36篇 |
综合类 | 2篇 |
化学工业 | 804篇 |
金属工艺 | 140篇 |
机械仪表 | 83篇 |
建筑科学 | 225篇 |
矿业工程 | 6篇 |
能源动力 | 114篇 |
轻工业 | 453篇 |
水利工程 | 30篇 |
石油天然气 | 17篇 |
无线电 | 315篇 |
一般工业技术 | 820篇 |
冶金工业 | 1160篇 |
原子能技术 | 48篇 |
自动化技术 | 593篇 |
出版年
2021年 | 42篇 |
2020年 | 40篇 |
2019年 | 46篇 |
2018年 | 59篇 |
2017年 | 66篇 |
2016年 | 80篇 |
2015年 | 66篇 |
2014年 | 81篇 |
2013年 | 244篇 |
2012年 | 137篇 |
2011年 | 205篇 |
2010年 | 145篇 |
2009年 | 154篇 |
2008年 | 182篇 |
2007年 | 151篇 |
2006年 | 128篇 |
2005年 | 109篇 |
2004年 | 116篇 |
2003年 | 115篇 |
2002年 | 104篇 |
2001年 | 88篇 |
2000年 | 82篇 |
1999年 | 88篇 |
1998年 | 262篇 |
1997年 | 171篇 |
1996年 | 153篇 |
1995年 | 110篇 |
1994年 | 108篇 |
1993年 | 113篇 |
1992年 | 61篇 |
1991年 | 50篇 |
1990年 | 57篇 |
1989年 | 45篇 |
1988年 | 49篇 |
1987年 | 49篇 |
1986年 | 51篇 |
1985年 | 87篇 |
1984年 | 71篇 |
1983年 | 57篇 |
1982年 | 75篇 |
1981年 | 77篇 |
1980年 | 96篇 |
1979年 | 82篇 |
1978年 | 65篇 |
1977年 | 78篇 |
1976年 | 67篇 |
1975年 | 53篇 |
1974年 | 32篇 |
1973年 | 37篇 |
1970年 | 20篇 |
排序方式: 共有4846条查询结果,搜索用时 343 毫秒
91.
The influence of externally located platinum on the isothermal stability of -Al2O3 scales formed at high temperatures has been examined. It has been observed that a nickel-base alloy forms an external scale of -Al2O3 during oxidation at 1200°C, but this scale breaks down isothermally, enabling a faster-growing Cr2O3-rich scale to develop. However, in the presence of platinum metal alongside the specimen in the furnace hot zone, the breakdown of the -Al2O3 scale is postponed for a substantial period of time. It appears that platinum, as the volatile species PtO2, is incorporated into the growing -Al2O3 scale where it either influences the stress relief mechanism at temperature or reduces oxidation growth stress generation and thus significantly enhances the isothermal stability of the scale. 相似文献
92.
Development of Habitat Suitability Criteria and In‐Stream Habitat Assessment for the Benthic Cyanobacteria Phormidium 下载免费PDF全文
Global demand for freshwater has led to unprecedented levels of water abstraction from riverine systems. This has resulted in large alterations in natural river flows. The deleterious impacts of reduced flows on fish and macroinvertebrate abundances have been thoroughly investigated; in contrast, there is a limited understanding of the potential for changes in the abundance of nuisance benthic algal/cyanobacterial blooms. In New Zealand, Phormidium sp. blooms are common in numerous rivers during summer low flows. In this study, an in‐stream habitat assessment is used to examine the relationship between Phormidium habitat availability and reducing flows. Over 650 observations of Phormidium mats, from seven sites (Hutt River, lower North Island, New Zealand), were used to construct habitat suitability curves for depth, velocity and substrate. Preference curves were fitted using both the ‘forage ratio’ and ‘quantile regression’ methods. Phormidium growth, observed at all seven sites, increased significantly from upstream (uppermost site, 5.2% mat cover) to downstream (63.5%). The habitat suitability curves revealed Phormidium had a large tolerance to velocity, depth and substrate type. Consequently, decreases in flow had only negligible effects on available Phormidium habitat. During periods of stable flow, Phormidium abundance positively correlated with increased nitrogen concentrations, potentially explaining the large variation in Phormidium cover from upstream to downstream. Quantile regression generated habitat suitability criteria were a more accurate predictor of available Phormidium habitat than the forage ratio criteria. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
93.
94.
95.
Mariana G. Figueiro Brittany Wood Barbara Plitnick Mark S. Rea 《Journal of the Society for Information Display》2013,21(10):417-421
Self‐luminous electronic devices emit optical radiation at short wavelengths, close to the peak sensitivity of melatonin suppression. The present paper investigated if light from a 178‐cm (70 in.) television suppressed melatonin. Results showed that light from televisions does not impact melatonin levels in the evening. 相似文献
96.
Flow cytometry has potential as a rapid assessment technique to evaluate phytoplankton biomass and species composition. It facilitates for multi-parameter analysis of individual cells on the basis of light scattering effects induced from cellular constituents, as well as auto-fluorescence. Fluorescence emission characteristics may be especially useful in classifying cyanobacteria as they contain phycoerythrin which emits light predominantly in the 550-600 nm waveband, chlorophyll-a (650-700 nm emission) and allophycocyanin (660 nm emission). The objective of our study was to assess the utility of flow cytometry for the rapid identification and sorting of freshwater algae and cyanobacteria species. Using a selection of laboratory-cultured freshwater algae and cyanobacteria species, this study demonstrated unique light scatter and fluorescent characteristics for each species examined, allowing for rapid species identification and sorting of mixed populations of laboratory cultures and samples from two lakes in the Rotorua region (New Zealand). Analysis of lake water samples collected over seven months demonstrated changes in abundance and community composition of phytoplankton in the two lakes and demonstrates that flow cytometry may be a useful technique for examining seasonal changes in phytoplankton composition. 相似文献
97.
Charles C. Wood 《Digital Creativity》2013,24(2-3):75-83
Abstract Though they have access to sophisticated authoring support systems, many authors use conventional media for the earliest stages of generating and organising ideas. This paper gives an overview of a study of six pairs of collaborating authors who were videoed in aprewriting task and who also underwent a structured post-interview concerning their use of external representations in the study and in their everyday work. Pairs were studied so that the behaviour was more externalised, there were natural verbal protocols and these protocols could be interpreted by the interlocutor rather than by the researcher. The analysis focuses on the part that the mediating representations play in the cognitive task and in coordinating cooperative cognition. The properties of the marks produced and the affordances of conventional media are considered. The study is interpreted within a ‘shared cognitive’ framework which draws on insights from distributed cognition, socially shared cognition, situated action and most importantly from Soviet psychology. It is suggested that the mediating representations perform two important and highly related functions. First, they support ‘idea sketching’ which is a form of reflexive communication where the individual mediates her own creative cognition through external representations. Second, they mediate cooperative cognition, providing the common grounding necessary to coordinate shared thought. 相似文献
98.
Davide Ciceri Lachlan R. Mason Dalton J. E. Harvie Jilska M. Perera Geoffrey W. Stevens 《Microfluidics and nanofluidics》2013,14(1-2):213-224
The use of a microfluidic device in determining the extraction kinetics of CoII ions by di-(2-ethylhexyl) phosphoric acid (DEHPA) was demonstrated. Experimental data obtained using a Y-Y-shaped microchannel were modelled using a finite volume method. The contributions of diffusion and reaction transport resistances to the overall rate of mass transfer were obtained. A diffusion-controlled transfer assumption could not account for the experimental data, confirming that transport occurs under a mixed reaction–diffusion resistance regime. The reaction rate constant was determined to be $(2.4 \pm 0.6) \times 10^{-10}$ m/s, in good agreement with corresponding Lewis cell measurements from the literature. 相似文献
99.
100.
Identifying discriminating variables between teachers who fully integrate computers and teachers with limited integration 总被引:1,自引:0,他引:1
Julie Mueller Eileen Wood Teena Willoughby Craig Ross Jacqueline Specht 《Computers & Education》2008,51(4):1523-1537
Given the prevalence of computers in education today, it is critical to understand teachers’ perspectives regarding computer integration in their classrooms. The current study surveyed a random sample of a heterogeneous group of 185 elementary and 204 secondary teachers in order to provide a comprehensive summary of teacher characteristics and variables that best discriminate between teachers who integrate computers and those who do not. Discriminant Function Analysis indicated seven variables for elementary teachers and six for secondary teachers (accounting for 74% and 68% of the variance, respectively) that discriminated between high and low integrators. Variables included positive teaching experiences with computers; teacher’s comfort with computers; beliefs supporting the use of computers as an instructional tool; training; motivation; support; and teaching efficacy. Implications for support of computer integration in the classroom are discussed. 相似文献