全文获取类型
收费全文 | 421361篇 |
免费 | 5970篇 |
国内免费 | 2287篇 |
专业分类
电工技术 | 7829篇 |
技术理论 | 5篇 |
综合类 | 3494篇 |
化学工业 | 64364篇 |
金属工艺 | 21051篇 |
机械仪表 | 16136篇 |
建筑科学 | 11157篇 |
矿业工程 | 3058篇 |
能源动力 | 8167篇 |
轻工业 | 31854篇 |
水利工程 | 5032篇 |
石油天然气 | 7716篇 |
武器工业 | 245篇 |
无线电 | 43346篇 |
一般工业技术 | 83008篇 |
冶金工业 | 60112篇 |
原子能技术 | 7065篇 |
自动化技术 | 55979篇 |
出版年
2021年 | 2817篇 |
2020年 | 1979篇 |
2019年 | 2497篇 |
2018年 | 23067篇 |
2017年 | 22597篇 |
2016年 | 16401篇 |
2015年 | 4179篇 |
2014年 | 5530篇 |
2013年 | 13592篇 |
2012年 | 13458篇 |
2011年 | 26150篇 |
2010年 | 22445篇 |
2009年 | 20097篇 |
2008年 | 21645篇 |
2007年 | 24174篇 |
2006年 | 9738篇 |
2005年 | 12583篇 |
2004年 | 10149篇 |
2003年 | 9469篇 |
2002年 | 8148篇 |
2001年 | 7061篇 |
2000年 | 6748篇 |
1999年 | 6490篇 |
1998年 | 13589篇 |
1997年 | 10082篇 |
1996年 | 7915篇 |
1995年 | 6063篇 |
1994年 | 5625篇 |
1993年 | 5504篇 |
1992年 | 4446篇 |
1991年 | 4121篇 |
1990年 | 4220篇 |
1989年 | 4170篇 |
1988年 | 3909篇 |
1987年 | 3423篇 |
1986年 | 3406篇 |
1985年 | 3897篇 |
1984年 | 3780篇 |
1983年 | 3487篇 |
1982年 | 3124篇 |
1981年 | 3328篇 |
1980年 | 2966篇 |
1979年 | 3179篇 |
1978年 | 3037篇 |
1977年 | 3119篇 |
1976年 | 3975篇 |
1975年 | 2734篇 |
1974年 | 2514篇 |
1973年 | 2575篇 |
1972年 | 2129篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The effect of the growth dynamics of heterotrophs on the composition and properties of peat lipids was demonstrated. Microbiological processes resulted in a considerable change in the amounts of water-soluble polysaccharide and polyphenol fractions. The lipid content remained practically unchanged under various model experiment conditions. In this case, an increase in the concentration of alkanes and the antioxidant activity of lipids was observed. The accumulation of antioxidants and an increase in the amount of chrysenes in lipids support the role of a microbiological factor in the origin of hydrocarbons. 相似文献
992.
An unconventional method of determining the color of clay and ceramic materials in air-dry and calcined states in equal-color coordinates of the color space using the color characteristics (saturation, hue, yellow hue, lightness, color coordinate) is employed to classify clays from the Gzhel’ deposit. The method is recommended for adjusting the color range of ceramic articles. 相似文献
993.
994.
995.
996.
997.
998.
999.
A. G. Upolovnikova V. M. Chumarev R. I. Gulyaeva L. Yu. Udoeva 《Russian Metallurgy (Metally)》2007,(1):10-13
The effect of sodium carbonate additions on phase formation during the air oxidation of the sublimates of niobium electron-beam remelting is studied by derivatography, X-ray diffraction analysis, and electron-probe microanalysis. The composition of the oxidation products changes with the heating temperature. The formation of sodium niobates and aluminates is detected by X-ray diffraction analysis at temperatures higher than 600°C. The oxidation of the sublimates is completed by the formation of sodium metaniobate and aluminate. Sodium carbonate additions are shown to accelerate the oxidation of the sublimates. 相似文献
1000.
Objective: Guided by the extended parallel process model (EPPM), the objective was to assess control processes dominant in influenza behavior decisions. Design: Cross-sectional survey. Results: Response rate was 31% (n=968). Regarding influenza risk, 59% were in danger control. Those in fear control were more likely to report influenza infection (p=.000). In the nonvaccinated, those in fear control were more likely to indicate not knowing where to get the vaccine (p=.016) and that it was unavailable (p=.027), and those in danger control believed they did not need it (p=.023). Zero critical values were more likely to indicate that no health provider recommended the shot (p=.002). Conclusions: Most perceived efficacy to be stronger than threat related to influenza; according to the EPPM, they are aware of their risk but recognize their ability to avert it. For those in danger control, messages should focus on increasing perceptions of severity and susceptibility to positively affect behavior change. For those in fear control, messages should focus on efficacy only. With a critical value of zero, no threat is induced, and a high-threat/high-efficacy approach should be taken. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献