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   301920篇
  免费   4219篇
  国内免费   830篇
电工技术   5108篇
综合类   173篇
化学工业   48322篇
金属工艺   12133篇
机械仪表   8874篇
建筑科学   7297篇
矿业工程   1875篇
能源动力   6978篇
轻工业   28806篇
水利工程   3341篇
石油天然气   7153篇
武器工业   18篇
无线电   32111篇
一般工业技术   59164篇
冶金工业   54540篇
原子能技术   7580篇
自动化技术   23496篇
  2021年   2504篇
  2019年   2335篇
  2018年   4297篇
  2017年   4233篇
  2016年   4528篇
  2015年   2943篇
  2014年   4850篇
  2013年   13193篇
  2012年   7779篇
  2011年   10006篇
  2010年   8213篇
  2009年   9265篇
  2008年   9536篇
  2007年   9408篇
  2006年   8188篇
  2005年   7607篇
  2004年   7110篇
  2003年   6832篇
  2002年   6865篇
  2001年   6654篇
  2000年   6315篇
  1999年   6418篇
  1998年   15785篇
  1997年   11674篇
  1996年   8976篇
  1995年   6737篇
  1994年   6101篇
  1993年   5996篇
  1992年   4535篇
  1991年   4506篇
  1990年   4345篇
  1989年   4355篇
  1988年   4312篇
  1987年   3650篇
  1986年   3643篇
  1985年   4217篇
  1984年   4004篇
  1983年   3648篇
  1982年   3467篇
  1981年   3610篇
  1980年   3465篇
  1979年   3385篇
  1978年   3467篇
  1977年   3999篇
  1976年   5181篇
  1975年   3167篇
  1974年   3020篇
  1973年   3033篇
  1972年   2656篇
  1971年   2474篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Ozonation is an innovative way to preserve high quality of seed during storage and it is an alternative to harmful organophosphorus agents. Disclosure of changes in the rapeseed oil under the influence of oxidative action of ozone on the seeds was the aim of the work and is presented for the first time. Two ozone concentrations and different length of ozonation were applied. The changes in tocopherols, phenolics, flavonoids contents, antiradical activity and oxidative stability were examined. The average vitamin E concentration was 33 mg per 100 g of oil before and 31.7 after ozonation of seeds. The average content of phenolic compounds was 14.3 mg of sinapic acid g−1 and 16.9 after the ozone treatment. Changes in the flavonoids content and antioxidant activity were observed too. Ozonation caused a decrease in the vitamin E concentration which resulted also in reducing the quenching of free radicals and reduction of oil induction time.  相似文献   
72.
73.
74.
The partitioning of predominant lipophilic olive bioactives (squalene, β-sitosterol and α-tocopherol) in olive oil processing was studied for the first time using common integrated olive milling plant. 7% of the oil and 5% of the squalene present in the olives was lost in the last pomace. β-sitosterol and α-tocopherol, which are mainly concentrated in the seed of the olive fruit, was recovered in virgin olive oil to a lesser extent (66%, 67%) while 10% were lost in last pomace. Thus, the loss of β-sitosterol and α-tocopherol was higher than that of squalene and oil, due to nonrecovered bound forms. 19% of the α-tocopherol and 21% of the β-sitosterol loss was unaccounted for, which can be attributed to degradation of α-tocopherol and incomplete recovery of sterols from the olive and pomace matrices. This study provides a basis for process development studies.  相似文献   
75.
Food Science and Biotechnology - The enzymatic activity and partial characterization of proteases from Bromelia karatas fruits were evaluated and compared with Bromelia pinguin proteases. The...  相似文献   
76.
From an experimental and theoretical investigation of the continuity of influent inorganic suspended solids (ISS) along the links connecting the primary settling tank (PST), fully aerobic or N removal activated sludge (AS) and anaerobic and aerobic sludge digestion unit operations, it was found that the influent wastewater (fixed) ISS concentration is conserved through primary sludge anaerobic digestion, activated sludge and aerobic digestion unit operations. However, the measured ISS flux at different stages through a series of wastewater treatment plant (WWTP) unit operations is not equal to the influent ISS flux, because the ordinary heterotrophic organisms (OHO) biomass contributes to the ISS flux by differing amounts depending on the active fraction of the VSS solids at that stage.  相似文献   
77.
Many models of spoken word recognition posit the existence of lexical and sublexical representations, with excitatory and inhibitory mechanisms used to affect the activation levels of such representations. Bottom-up evidence provides excitatory input, and inhibition from phonetically similar representations leads to lexical competition. In such a system, long words should produce stronger lexical activation than short words, for 2 reasons: Long words provide more bottom-up evidence than short words, and short words are subject to greater inhibition due to the existence of more similar words. Four experiments provide evidence for this view. In addition, reaction-time-based partitioning of the data shows that long words generate greater activation that is available both earlier and for a longer time than is the case for short words. As a result, lexical influences on phoneme identification are extremely robust for long words but are quite fragile and condition-dependent for short words. Models of word recognition must consider words of all lengths to capture the true dynamics of lexical activation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
78.
The Chelyabinsk Metallurgical Combine has periodically used Kachkanar agglomerate to make conversion pig iron since 1972. Use of this material reached a peak in 1998, when it comprised an average of 27.1% of the charge. In some months, the amount of this material charged into the furnace reached highs of 45.6 and 74.1% on certain furnaces. The coolers on the iron notches of furnaces 4 and 5 burned during that year, the quality of the smelting products and the condition of the ladles rapidly deteriorated, and the smelting rate declined. No Kachkanar agglomerate was used in 2000–2001, but it was again added to the charge in February 2002. The amount used was smaller than previously, averaging 10.7% for the shop as a whole. It was determined that using a charge with 15% Kachkanar agglomerate has both positive and negative consequences. N. N. Gorshkov, A. V. Denisov, and V. Kh. Barinov also participated in this study. __________ Translated from Metallurg, No. 3, pp. 43–45, March, 2006.  相似文献   
79.
While the motion of twist boundaries can be readily studied by atomistic simulations with molecular dynamics (MD) under the action of an elastic driving force, the approach fails for tilt boundaries. This is due to the interaction of the elastic stress with the grain boundary (GB) structure, which causes plastic strain by GB sliding. A novel concept, the orientation correlated driving force, is introduced to circumvent this problem. It is shown that this concept can be successfully applied to the study of the migration of tilt boundaries. The migration behavior of several twist and tilt GBs was investigated. The transition from low-to high-angle boundaries can be captured, and a structural transition of tilt boundaries was found at high temperatures, which also affected the migration behavior. The results compare well with experimental results of the motion high-angle boundaries, but for low-angle boundaries, the agreement is poor. This article is based on a presentation made in the “Hillert Symposium on Thermodynamics & Kinetics of Migrating Interfaces in Steels and Other Complex Alloys,” December 2–3, 2004, organized by The Royal Institute of Technology in Stockholm, Sweden.  相似文献   
80.
This paper addresses the impact of device macromodels on the accuracy of signal integrity and performance predictions for critical digital interconnecting systems. It exploits nonlinear parametric models for both single-ended and differential devices, including the effects of power supply fluctuations and receiver bit detection. The analysis demonstrates that the use of well-designed macromodels dramatically speeds up the simulation as well it preserves timing accuracy even for long bit sequences.  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