首页 | 官方网站   微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   394815篇
  免费   5183篇
  国内免费   703篇
工业技术   400701篇
  2021年   3602篇
  2020年   2902篇
  2019年   3432篇
  2018年   23273篇
  2017年   22863篇
  2016年   18509篇
  2015年   4899篇
  2014年   6937篇
  2013年   12964篇
  2012年   13492篇
  2011年   23087篇
  2010年   20048篇
  2009年   17622篇
  2008年   19010篇
  2007年   20416篇
  2006年   7660篇
  2005年   9404篇
  2004年   8456篇
  2003年   8179篇
  2002年   6760篇
  2001年   5522篇
  2000年   5648篇
  1999年   4875篇
  1998年   10292篇
  1997年   7665篇
  1996年   5513篇
  1995年   4354篇
  1994年   4046篇
  1993年   4218篇
  1992年   3409篇
  1991年   3591篇
  1990年   3663篇
  1989年   3536篇
  1988年   3430篇
  1987年   3407篇
  1986年   3308篇
  1985年   3492篇
  1984年   3406篇
  1983年   3247篇
  1982年   3121篇
  1981年   3180篇
  1980年   3203篇
  1979年   3361篇
  1978年   3577篇
  1977年   3629篇
  1976年   4295篇
  1975年   3288篇
  1974年   3350篇
  1973年   3400篇
  1972年   3018篇
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
51.
The corrosion mechanisms of T24, T92, VM12, and AISI 304 steels are studied under the influence of NaCl–KCl, NaCl–Na2SO4, and KCl–K2SO4 salt mixtures in a dry air atmosphere at 650°C for 15 days. NaCl–KCl was the most aggressive deposit and AISI 304 stainless steel exhibited the highest corrosion resistance. There was no relation between the Cr content of the ferritic steels and their corrosion resistance in NaCl–KCl. In contrast, the resistance of high-Cr steels was better when exposed to NaCl–Na2SO4 and KCl–K2SO4. The high-Cr and the low-Cr steels were more susceptible to NaCl–Na2SO4 and to KCl–K2SO4, respectively.  相似文献   
52.
Golubev  N. V.  Ignat’eva  E. S.  Maurus  A. A.  Ziyatdinova  M. Z.  Lopatina  E. V.  Lorenzi  R.  Paleari  A.  Sigaev  V. N. 《Glass and Ceramics》2021,77(11-12):415-418
Glass and Ceramics - The influence of Al2O3 as an additive and the heat-treatment regime on the luminescence spectra of gallate glass-ceramics was investigated. It is shown that its luminescence...  相似文献   
53.
Russian Engineering Research - Models based on regression analysis for predicting the operational efficiency of high-pressure roller crushers are considered. A systematized and structured...  相似文献   
54.
Journal of Machinery Manufacture and Reliability - A device based on smart alloys has been designed for use in machine building items, in particular, in nuclear engineering, for preventing...  相似文献   
55.
Russian Engineering Research - The strategic efficiency of a project is defined. An approach to assessing the strategic efficiency of projects is outlined. This approach, incorporated in the State...  相似文献   
56.
57.
58.
JOM - Refractory high-entropy alloys (RHEAs) are potential candidate materials for use in next-generation nuclear reactors due to their excellent mechanical performance at high temperatures. Here,...  相似文献   
59.
The objective of this study was to determine the effect of temperature on whole milk density measured at four different temperatures: 5, 10, 15, and 20 °C. A total of ninety-three individual milk samples were collected from morning milking of thirty-two Holstein Friesian dairy cows, of national average genetic merit, once every two weeks over a period of 4 weeks and were assessed by Fourier transform infrared spectroscopy for milk composition analysis. Density of the milk was evaluated using two different analytical methods: a portable density meter DMA35 and a standard desktop model DMA4500M (Anton Paar GmbH, UK). Milk density was analysed with a linear mixed model with the fixed effects of sampling period, temperature and analysis method; triple interaction of sampling period x analysis method x temperature; and the random effect of cow to account for repeated measures. The effect of temperature on milk density (ρ) was also evaluated including temperature (t) as covariate with linear and quadratic effects within each analytic method. The regression equation describing the curvature and density–temperature relationship for the DMA35 instrument was ρ = 1.0338−0.00017T−0.0000122T2 (R2 = 0.64), while it was ρ = 1.0334 + 0.000057T−0.00001T2 (R2 = 0.61) for DMA4500 instrument. The mean density determined with DMA4500 at 5 °C was 1.0334 g cm−3, with corresponding figures of 1.0330, 1.0320 and 1.0305 g cm−3 at 10, 15 and 20 °C, respectively. The milk density values obtained in this study at specific temperatures will help to address any bias in weight–volume calculations and thus may also improve the financial and operational control for the dairy processors in Ireland and internationally.  相似文献   
60.
Protection of Metals and Physical Chemistry of Surfaces - The stage mechanism of manganese-containing conversion coatings (MCCs) formation on the surface of AD31 alloy (AA6063) in acidic (pH 3)...  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司    京ICP备09084417号-23

京公网安备 11010802026262号