全文获取类型
收费全文 | 1318篇 |
免费 | 80篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 15篇 |
综合类 | 1篇 |
化学工业 | 386篇 |
金属工艺 | 34篇 |
机械仪表 | 50篇 |
建筑科学 | 37篇 |
矿业工程 | 4篇 |
能源动力 | 23篇 |
轻工业 | 219篇 |
水利工程 | 12篇 |
石油天然气 | 11篇 |
无线电 | 64篇 |
一般工业技术 | 282篇 |
冶金工业 | 123篇 |
原子能技术 | 11篇 |
自动化技术 | 128篇 |
出版年
2024年 | 4篇 |
2023年 | 20篇 |
2022年 | 40篇 |
2021年 | 67篇 |
2020年 | 30篇 |
2019年 | 44篇 |
2018年 | 51篇 |
2017年 | 62篇 |
2016年 | 60篇 |
2015年 | 30篇 |
2014年 | 44篇 |
2013年 | 97篇 |
2012年 | 78篇 |
2011年 | 70篇 |
2010年 | 69篇 |
2009年 | 65篇 |
2008年 | 55篇 |
2007年 | 54篇 |
2006年 | 46篇 |
2005年 | 32篇 |
2004年 | 30篇 |
2003年 | 28篇 |
2002年 | 42篇 |
2001年 | 24篇 |
2000年 | 17篇 |
1999年 | 22篇 |
1998年 | 56篇 |
1997年 | 36篇 |
1996年 | 28篇 |
1995年 | 24篇 |
1994年 | 17篇 |
1993年 | 14篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 7篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 1篇 |
排序方式: 共有1400条查询结果,搜索用时 15 毫秒
91.
ISO Recommended Reference Radiations for the Calibration and Proficiency Testing of Dosemeters and Dose Rate Meters used in Radiation Protection 总被引:1,自引:0,他引:1
92.
Perennec A. Soares R. Jarry P. Legaud P. Goloubkoff M. 《Microwave Theory and Techniques》1989,37(9):1475-1478
In very-high-data-rate fiber-optic systems, it is necessary to have an ultrawideband, high-gain, low-noise amplifier after the front end. The authors show how powerful analytical techniques, such as the real frequency technique, can be applied to the design of a 4-MHz-7-GHz amplifier. A two-stage monolithic amplifier designed according to the theory gives 17-dB gain; a three-stage hybrid amplifier exhibits 16-dB gain across the same frequency band. The gain, noise figure, and pulse response of each amplifier are presented 相似文献
93.
Isabel C.F.R. Ferreira Lillian Barros Maria Elisa Soares Maria Lourdes Bastos José Alberto Pereira 《Food chemistry》2007,103(1):188-195
Olive trees (Olea europaea L. Cv. Cobrançosa) from the northeast of Portugal were sprayed with three different copper formulations [bordeaux mixture (copper sulphate + calcium hydroxide − 20% Cu), copper hydroxide (40% Cu) and copper oxychloride (50% Cu)] to control olive fungal diseases. The residues of copper in olive leaves, harvested at different times, were evaluated by atomic absorption spectrometry. At all the collection times, treated olive leaves had significantly higher copper contents, compared to the control. The different copper amounts in pesticide formulations lowered the leaves contents in total phenols and hence their antioxidant properties. Olive leaves sprayed with copper oxychloride possessed the highest copper levels and the lowest content in phenols, which influenced its antioxidant activity (higher EC50 values for reducing power, scavenging effect on DPPH radicals and inhibition of erythrocyte hemolysis). Leaves without copper residues proved to be a good natural source of antioxidants, giving values comparable to the reference compounds. 相似文献
94.
95.
Nilda de Ftima Ferreira Soares Robson M. Geraldine Rolf Pushmann Csar Silva Teles 《Packaging Technology and Science》2002,15(3):109-114
Minimum processing associated with an adequate packing system has shown good results in preserving a large group of perishable horticultural produce. The present work was done to determine the effect of the number of layered of low‐density polyethylene (LDPE) or polyvinyl chloride (PVC) film on the quality of minimally processed packed garlic (Allium sativum), known for its short shelf‐life. Polystyrene trays containing 200 g garlic bulbils were wrapped in one to four layers of PVC or one or two layers of LDPE and stored at room temperature. Changes in weight, bulbil colouration, in‐package gas composition and apparent quality were monitored for 14 days. Best results were obtained by wrapping the packages in four layers of PVC film, with insignificant weight loss (5%), changes in colour tone and saturation, and the in‐pack atmosphere (O2 = 0.01% and CO2 = 13.5%) inhibited fungal growth, extending shelf‐life to 13 days at 25 ± 2°C. On the other hand, the high in‐package moisture in LDPE wrapping favoured fungal growth, rapidly depreciating bulbil quality. The shelf‐life of minimally processed garlic can be increased by maintaining an adequate in‐pack atmosphere, which can be achieved by using four layers of PVC or a another film of similar permeability. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
96.
97.
The objective was to assess food consumption among children attending non-profit nurseries in the Federal District, Brazil.A representative sample was obtained and stratified by income. Food intake among 678 children, between 4 and 82 months old, was analyzed in nine nurseries using the 24-h dietary recall and direct food weighing methods. In children under 13 months old mean intake was above AI between 93.6 to 100% for carbohydrates, proteins, vitamins B1, B2, B12, B6, and zinc. In children from 7-12 months 56.5% presented iron consumption below EAR. Calcium intake was above AI for 35.4% of children over 1 year old. For vitamins with EAR values, the prevalence of inadequate consumption was 53.2% for vitamin E, and 90% for folate for children over 12 months old. Iron and zinc intake was above UL for 6.4% and 32.5% of children under 1 year old, and 1.5% and 5.3% for the remaining children, respectively. Lipid percentage distribution range among children between 13 and 47 months old was within the acceptable range for only 16.2%. Nonetheless, children between 36 and 82 months of both genders presented mean intake below energy requirements. Inadequate consumption observed for some nutrients points to the need for improvements in the standard of meals and nutritional assistance offered to children enrolled in charitably run nurseries in the Federal District. 相似文献
98.
Paulo H. S. Picciani Eliton S. Medeiros Zhongli Pan Delilah F. Wood William J. Orts Luiz H. C. Mattoso Bluma G. Soares 《大分子材料与工程》2010,295(7):618-627
Conducting electrospun fiber mats based on PLA and PAni blends were obtained with average diameter values between 87 and 1 006 nm with PAni quantities from 0 to 5.6 wt.‐%. Structural characteristics of fiber mats were compared to cast films with the same amount of PAni and studied by SEM, SAXS, and AFM. Thermal properties of fiber mats and cast films were compared by DSC analyses. Mechanical properties of fiber mats were also evaluated. It was found that electrospinning process governs the crystal structure of the fibers and strongly affects fiber properties. New properties of PLA/PAni blends are reported due to the size fiber reduction.
99.
Juliana Mendes de Oliveira Iara Alves Anes Jorge Luís Coleti Denise Crocce Romano Espinosa Marcelo Siqueira de Carvalho Jorge Alberto Soares Tenório 《加拿大化工杂志》2023,101(4):1743-1761
Niobium (Nb) and Tantalum (Ta) are used to increase materials' mechanical resistance and produce lighter alloys. Worldwide Nb production reached 78 000 t in 2020. The reduced ore offer justifies the recycling of these metals from tin slag, contributing to the circular economy. Nb2O5 and Ta2O5 extraction either from the primary source or the tin slag is an industrial challenge. Nb and Ta dissolution processes already implemented are fluoride leaching, sulphuric leaching, alkaline leaching, and alkaline roasting. The fluoride process raises environmental concerns about waste control. The sulphuric method can be managed to have higher Nb and Ta extraction in a less aggressive process, if some changes are implemented, such as increasing the number of extraction steps, decreasing the pulp density, or increasing the temperature; however, the efficiency of this methodology must be tested for tin slag. The alkaline method seems to be more selective to Nb and Ta by reactants and temperature control. Despite those well-established Nb and Ta treatments, they must be adapted to recover Nb and Ta from slag. The slag has low Nb and Ta content, while high Si and Ca concentrations exist in the matrix. This paper brings the main methods used to extract the Nb and Ta from the primary resources and an overview of Nb and Ta recovery from the slag. This investigation comes as a tool to guide the development of new methods to recover Nb and Ta from low-grade sources such as tin slag. 相似文献