首页 | 本学科首页   官方微博 | 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   743698篇
  免费   23899篇
  国内免费   2968篇
电工技术   14366篇
技术理论   5篇
综合类   1654篇
化学工业   121698篇
金属工艺   27796篇
机械仪表   21154篇
建筑科学   19255篇
矿业工程   3671篇
能源动力   19267篇
轻工业   70017篇
水利工程   7512篇
石油天然气   13430篇
武器工业   282篇
无线电   85066篇
一般工业技术   145786篇
冶金工业   140843篇
原子能技术   14103篇
自动化技术   64660篇
  2021年   7073篇
  2020年   6256篇
  2019年   9059篇
  2018年   12837篇
  2017年   12904篇
  2016年   13926篇
  2015年   11025篇
  2014年   15769篇
  2013年   37325篇
  2012年   22676篇
  2011年   29591篇
  2010年   24046篇
  2009年   26013篇
  2008年   26670篇
  2007年   26135篇
  2006年   22910篇
  2005年   20504篇
  2004年   19280篇
  2003年   18685篇
  2002年   18035篇
  2001年   17977篇
  2000年   16794篇
  1999年   17089篇
  1998年   42379篇
  1997年   30023篇
  1996年   22840篇
  1995年   17062篇
  1994年   15046篇
  1993年   14697篇
  1992年   10753篇
  1991年   9967篇
  1990年   9914篇
  1989年   9611篇
  1988年   8944篇
  1987年   7859篇
  1986年   7831篇
  1985年   8739篇
  1984年   8277篇
  1983年   7374篇
  1982年   6858篇
  1981年   7104篇
  1980年   6648篇
  1979年   6653篇
  1978年   6386篇
  1977年   7451篇
  1976年   9890篇
  1975年   5627篇
  1974年   5235篇
  1973年   5403篇
  1972年   4445篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
82.
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   
83.
Theoretical Foundations of Chemical Engineering - New research results, as well as those published earlier by the authors, on the synthesis of azo compounds based on nitroanilines obtained by the...  相似文献   
84.
Polymer Bulletin - In this study, we synthesized a new ion-imprinted polymer (IIP) based on introduction of amidoxime groups in acrylonitrile, complexation with Cd2+ ions and polymerization with...  相似文献   
85.
A hybrid sorbent material for removal of hydrogen sulfide from air was developed. The material is based on activated carbon and iron compounds obtained from waste iron(II) sulfate(VI) heptahydrate. The iron salt is deposited on the carbonaceous support and subjected to oxidation (Fe2+ to Fe3+) using atmospheric oxygen under alkaline conditions. An effect of H2O2 addition to the process on the composition of the resultant material was also examined. X-ray diffraction (XRD) analyses confirmed easy conversion of waste FeSO4·7H2O to iron oxides Fe3O4 and FeOOH. The activated carbon supporting iron oxides revealed a higher efficiency in H2S elimination from air compared to the commercial activated carbon, without any modification.  相似文献   
86.
At the hydroelectric unit No. 11 of the Nizhnekamsk hydroelectric power plant, the filling wedges of a rotor were investigated by ultrasound in the free st  相似文献   
87.
The price of cobalt has increased by some 450% in the past two years, mainly due to increasing demand for lithium–ion batteries. With an official 2017 production of 64 kt, the Democratic Republic of Congo produces more than half of the world’s cobalt. African Copperbelt operations have traditionally focused on copper production; however, it has now become imperative to also consider cobalt recovery from these ores. A plethora of processing routes is possible. Most hydrometallurgical flowsheets recover cobalt from the raffinate of the low-grade copper solvent-extraction circuit. Downstream purification processes include sequential precipitation with a variety of reagents, solvent extraction, and ion exchange. Product choices include hydroxide, carbonate, sulfate, and metal cathode. This study assesses technical and economic advantages and limitations of various approaches to the hydrometallurgical processing of cobalt in an African context.  相似文献   
88.
Journal of Communications Technology and Electronics - Abstract—The article presents a rigorous numerical solution, using the Wiener–Hopf method, to the problem of plane wave...  相似文献   
89.
The proliferating need for sustainability intervention in food grain transportation planning is anchoring the attention of researchers in the interests of stakeholders and environment at large. Uncertainty associated with food grain supply further intensifies the problem steering the need for designing robust, cost-efficient and sustainable models. In line with this, this paper aims to develop a robust and sustainable intermodal transportation model to facilitate single type of food grain commodity shipments while considering procurement uncertainty, greenhouse gas emissions, and intentional hub disruption. The problem is designed as a mixed integer non-linear robust optimisation model on a hub and spoke network for evaluating near optimal shipment quantity, route selection and hub location decisions. The robust optimisation approach considers minimisation of total relative regret associated with total cost subject to several real-time constraints. A version of Particle Swarm Optimisation with Differential Evolution is proposed to tackle the resulting NP-hard problem. The model is tested with two other state-of the art meta-heuristics for small, medium, and large datasets subject to different procurement scenarios inspired from real time food grain operations in Indian context. Finally, the solution is evaluated with respect to total cost, model and solution robustness for all instances.  相似文献   
90.
Urbano  Cristóbal  Ardanuy  Jordi 《Scientometrics》2020,124(1):575-602
Scientometrics - The interdisciplinary nature of library and information science (LIS) research has been highlighted for some time now. The term “interdisciplinary” is used primarily in...  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