全文获取类型
收费全文 | 1810篇 |
免费 | 38篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 12篇 |
化学工业 | 300篇 |
金属工艺 | 13篇 |
机械仪表 | 76篇 |
建筑科学 | 94篇 |
矿业工程 | 3篇 |
能源动力 | 31篇 |
轻工业 | 187篇 |
水利工程 | 18篇 |
石油天然气 | 6篇 |
无线电 | 229篇 |
一般工业技术 | 187篇 |
冶金工业 | 475篇 |
原子能技术 | 18篇 |
自动化技术 | 200篇 |
出版年
2022年 | 15篇 |
2021年 | 28篇 |
2020年 | 16篇 |
2019年 | 23篇 |
2018年 | 31篇 |
2017年 | 29篇 |
2016年 | 29篇 |
2015年 | 12篇 |
2014年 | 42篇 |
2013年 | 79篇 |
2012年 | 45篇 |
2011年 | 54篇 |
2010年 | 38篇 |
2009年 | 54篇 |
2008年 | 67篇 |
2007年 | 64篇 |
2006年 | 49篇 |
2005年 | 47篇 |
2004年 | 35篇 |
2003年 | 40篇 |
2002年 | 45篇 |
2001年 | 32篇 |
2000年 | 39篇 |
1999年 | 28篇 |
1998年 | 131篇 |
1997年 | 65篇 |
1996年 | 55篇 |
1995年 | 44篇 |
1994年 | 34篇 |
1993年 | 51篇 |
1992年 | 28篇 |
1991年 | 20篇 |
1990年 | 32篇 |
1989年 | 30篇 |
1988年 | 15篇 |
1987年 | 18篇 |
1986年 | 26篇 |
1985年 | 27篇 |
1984年 | 28篇 |
1983年 | 17篇 |
1982年 | 19篇 |
1981年 | 25篇 |
1980年 | 28篇 |
1979年 | 20篇 |
1978年 | 20篇 |
1977年 | 24篇 |
1976年 | 37篇 |
1975年 | 14篇 |
1974年 | 12篇 |
1973年 | 15篇 |
排序方式: 共有1849条查询结果,搜索用时 15 毫秒
111.
112.
A porcelain faucet handle failed after years of use in a residential rental property. Determining the cause of failure was hampered by the fact that the failed handle was no longer available. The analysis included mechanical testing of exemplar faucet handles to measure the reasonable forces that could be applied by hand and the forces necessary to cause failure. Interface geometry between the porcelain handle and the interior metal nut was a factor. Finite Element Analysis facilitated the study. Results showed that if the faucet handle had sustained damage during a gasket repair, then the failure could be accounted for. 相似文献
113.
This paper reports on a design science research study that seeks to investigate how information service components affect consumers’ potential adoption of such services. More specifically, the paper develops a conceptual model that uses the theory of organizational information services (TOIS) and the unified theory of acceptance and use of technology (UTAUT) as a basis. The results indicate that individual constructs can be linked to service components. In turn, this result can potentially be instrumental in progress toward a deeper understanding of consumers’ adoption of information services and how this affects the development of such services and systems that support them. 相似文献
114.
A. C. L. Sá J. M. C. Pereira R. H. Gardner 《International journal of remote sensing》2013,34(16):3583-3601
Fires in Africa affect atmospheric emissions and carbon sequestration, landscape patterns, and regional and global climatic conditions. Studies of these effects require accurate estimation of the extent of measurable fire events. The goal of this study was to assess the influence of burned area spatial patterns on the spectral detectability of burned areas. Six Landsat‐7 ETM+ images from the southern Africa were used for burned area mapping and spatial pattern analysis, while contemporaneous MODIS 500 m spatial resolution images were used to measure the spectral detectability of burned areas. Using a 15 by 15 km sample quadrats analysis, we showed that above a burned area proportion threshold of approximately 0.5 the spectral detectability of burned areas increase due to the decrease in the number of mixed pixels. This was spatially related to the coalescence of burned patches and the decrease in the total burned area perimeter. Simple burned area shapes were found at the Botswana site, where the absence of tree cover and the presence of bright surfaces (soil and dry grass) enhanced the spectral contrast of the burned surfaces, thus enabling better estimates of burned area extent. At the Zambia and Congo sites, landscape fragmentation due to human activity and the presence of a tree vegetation layer, respectively, contribute to the presence of small burned area patches, which may remain undetectable using moderate spatial resolution satellite imagery, leading to less accurate burned area extent estimates. 相似文献
115.
116.
Schmitz Joy M.; Lindsay Jan A.; Stotts Angela L.; Green Charles E.; Moeller F. Gerard 《Canadian Metallurgical Quarterly》2010,18(3):238
New data support use of levodopa pharmacotherapy with behavioral contingency management (CM) as one efficacious combination in cocaine dependence disorder treatment. A potential mechanism of the combined treatment effects may be related to dopamine-induced enhancement of the saliency of contingently delivered reinforcers. Evidence to support this mechanism was sought by evaluating levodopa-enhancing effects across distinct CM conditions that varied in behavioral targets. A total of 136 treatment-seeking, cocaine dependent subjects participated in this 12-week, randomized, placebo-controlled trial of levodopa (vs. placebo) administered in combination with one of three behavioral CM conditions. In the CM-URINE condition, subjects received cash-valued vouchers contingent on cocaine-negative urine toxicology results. In the CM-ATTEND condition, the same voucher schedule was contingent on attending thrice weekly clinic visits. In the CM-MEDICATION condition, the same voucher schedule was contingent on Medication Event Monitoring Systems- and riboflavin-based evidence of pill-taking behavior. Primary outcomes associated with each CM target behavior were analyzed using generalized linear mixed models for repeated outcomes. CM responding in the CM-ATTEND and CM-MEDICATION conditions showed orderly effects, with each condition producing corresponding changes in targeted behaviors, regardless of medication condition. In contrast, CM responding in the CM-URINE condition was moderated by medication, with levodopa-treated subjects more likely to submit cocaine-negative urines. These findings specify the optimal target behavior for CM when used in combination with levodopa pharmacotherapy. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
117.
HCI and the older population 总被引:1,自引:0,他引:1
118.
A Functional Explanation for Patterns of Norditerpenoid Alkaloid Levels in Tall Larkspur (Delphinium barbeyi) 总被引:1,自引:0,他引:1
Concentrations of norditerpenoid alkaloids vary among larkspur (Delphinium) species, locations, and years, but environmental stresses seem to have little effect on alkaloid levels. There is a need for a functional hypothesis of alkaloid synthesis and metabolism to explain the observed trends in concentration and to predict the toxicity of larkspur populations. This study was replicated at two locations over two years in the mountains of central Utah. Ten tall larkspur (D. barbeyi) plants were marked at each location, and a single stalk was harvested from each plant at weekly intervals throughout the growing season. Concentrations of toxic and total alkaloids were measured by Fourier-transformed infrared spectroscopy (FTIR), and alkaloid pools were calculated by multiplying the alkaloid concentration by the dry weight of the plant to determine the amount of alkaloids in the stalk. Alkaloid pools in the stalks increased for the first three weeks, leveled off, and then declined to low levels as the plants began to senesce. Concentrations of alkaloids declined through the season, as the alkaloids were diluted in the increasing biomass as the plants grew. These patterns will be used to predict potential toxicity of larkspur populations. 相似文献
119.
Tailoring magnetic and dielectric properties of rubber ferrite composites containing mixed ferrites 总被引:1,自引:0,他引:1
M. R. Anantharaman K. A. Malini S. Sindhu E. M. Mohammed S. K. Date S. D. Kulkarni P. A. Joy Philip Kurian 《Bulletin of Materials Science》2001,24(6):623-631
Rubber ferrite composites containing various mixed ferrites were prepared for different compositions and various loadings.
The magnetic and dielectric properties of the fillers as well as the ferrite filled matrixes were evaluated separately. The
results are correlated. Simple equations are proposed to predetermine the magnetic and dielectric properties. The validity
of these equations is verified and they are found to be in good agreement. These equations are useful in tailoring the magnetic
and dielectric properties of these composites with predetermined properties. 相似文献
120.
The use of coal liquefaction catalysts for coal/oil coprocessing and heavy oil upgrading 总被引:2,自引:0,他引:2
A. V. Cugini K. S. Rothenberger D. Krastman M. V. Ciocco R. L. Thompson C. McCreary T. J. Gardner 《Catalysis Today》1998,43(3-4):291-303
The catalytic hydrogenation of heavy oil and mixed coal-heavy oil (coprocessing) systems has been the focus of a recent study at the Federal Energy Technology Center (FETC). The intent of this effort was to extend the use of coal liquefaction technologies to heavy oil upgrading and coprocessing systems. Specifically, new dispersed molybdenum-based catalysts developed at FETC and a novel silica-doped hydrous titanium oxide (HTO : Si)-supported NiMo catalyst developed at Sandia National Laboratories (SNL) were tested in these systems. The results indicate the potential of coal liquefaction catalysts for use in coprocessing and heavy oil upgrading. High conversions of coal–oil mixtures were observed with dispersed catalyst loadings as low as 100 ppm Mo. Similar results were observed in heavy oil systems. Also, the novel NiMo/HTO : Si catalyst was at least as effective as commercially-available supported catalysts (e.g. Amocat 1C) for conversion of high boiling point material to distillable products and aromatics removal. 相似文献