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   168514篇
  免费   1172篇
  国内免费   193篇
电工技术   2553篇
综合类   119篇
化学工业   26611篇
金属工艺   9471篇
机械仪表   5715篇
建筑科学   3008篇
矿业工程   1887篇
能源动力   2703篇
轻工业   8815篇
水利工程   2729篇
石油天然气   8692篇
武器工业   12篇
无线电   14492篇
一般工业技术   38250篇
冶金工业   27794篇
原子能技术   6933篇
自动化技术   10095篇
  2018年   2977篇
  2017年   3091篇
  2016年   3344篇
  2015年   1672篇
  2014年   2954篇
  2013年   6338篇
  2012年   4311篇
  2011年   5397篇
  2010年   4420篇
  2009年   4894篇
  2008年   4940篇
  2007年   4868篇
  2006年   4141篇
  2005年   3819篇
  2004年   3634篇
  2003年   3520篇
  2002年   3450篇
  2001年   3463篇
  2000年   3361篇
  1999年   3212篇
  1998年   7018篇
  1997年   5148篇
  1996年   3821篇
  1995年   2916篇
  1994年   2593篇
  1993年   2720篇
  1992年   2254篇
  1991年   2304篇
  1990年   2409篇
  1989年   2315篇
  1988年   2313篇
  1987年   2190篇
  1986年   2246篇
  1985年   2292篇
  1984年   2206篇
  1983年   2135篇
  1982年   1980篇
  1981年   2193篇
  1980年   2053篇
  1979年   2269篇
  1978年   2431篇
  1977年   2430篇
  1976年   3095篇
  1975年   2244篇
  1974年   2307篇
  1973年   2342篇
  1972年   2155篇
  1971年   1911篇
  1970年   1701篇
  1969年   1632篇
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
111.
112.
Ellagic acid (2, 3, 7, 8‐tetrahydroxy(1)benzopyrano(5, 4, 3‐cde)(1)benzopyran‐5, 10‐dione) was selected as a model pollutant which is present in the tannic fraction of cork processing wastewater. The ultrafiltration of aqueous ellagic acid solutions through three membranes was studied in tangential UF laboratory equipment. Two of the membranes were polyethersulfone (Biomax10K and Biomax5K, with MWCO of 10000 and 5000 Da, respectively), and the third made of regenerated cellulose (Ultracel5K, with MWCO of 5000 Da). The water hydraulic permeability was evaluated for each membrane. The evolution of the permeate flow rate with processing time was followed, and the influence of the main operating variables (feed flow rate, trans‐membrane pressure and nature of the membranes) on the permeate flux was also established. According to the hypothesis of the film theory, the intrinsic and apparent rejection coefficients, as well as the mass transfer coefficients, were also determined, and the values obtained were discussed as a function of the operating conditions used.  相似文献   
113.
114.
115.
Networkable Windows-based operating system devices present information security challenges to both vendors and users of such devices. This article highlights some of those threats and offers measures to improve the link between a firm's business strategy, its operational activities, and its information security strategy.  相似文献   
116.
117.
Given the heightened interest in nutritional aspects of exercise, and an increase in athletic participation by women, it appeared timely to review the nutritional implications of exercise in women. The initial part of this paper contains a compilation of published studies on the nutrient intakes of female athletes. These reveal that most groups of athletes have adequate nutrient intakes, and that their vitamin and mineral intakes appear to be superior to those of nonathletic women. The average energy intake of athletes in studies summarized in this paper was 2069 kcal, and for certain groups of athletes, energy intakes were even lower. How these women manage to train intensely while consuming energy intakes similar to those of sedentary women is not readily apparent, and for this reason, the remainder of the paper discusses energy balance as affected by activity. Methodological considerations related to assessment of the components of the energy balance equation (food intake, energy expenditure, and body energy stores) are presented, with a focus on considerations in women. The effects of activity on each of these components are then discussed in an attempt to determine whether some form of energy conservation may occur. Finally, effects of activity on the menstrual cycle are reviewed. The observed changes are discussed in relation to nutrition 1) in terms of how nutrition may play a role in their causation; and 2) in terms of their nutritional implications for the amenorrheic athlete, specifically as regards energy balance and bone density.  相似文献   
118.
The results of the synthesis of ceramic pigments using coprecipitation of hydroxides and difficultly soluble salts of multivalent metal ions are described. The specifics of the coprecipitation process and the effect of various factors on the production of the initial precipitates for subsequent synthesis of ceramic pigments are analyzed. The technology of pigment production is described. __________ Translated from Steklo i Keramika, No. 6, pp. 37 – 39, June, 2005.  相似文献   
119.
120.
The study suggests improvements in the design of new houses to conserve energy and enhance indoor thermal comfort. Summer temperature records show that a new house has an average indoor temperature of 35°C with the ambient average 31°C. The traditional house in the old city recorded 28°C for the same period. Winter temperatures in both types of houses were similar (12°C) when not occupied. Architectural features of the two houses were compared to identify those responsible for difference in the thermal performance. Larger exposed surface and window areas, higher overall heat transfer coefficient and weaker thermal coupling with the ground for the new houses seems to contribute to their inferior thermal performance.  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