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   470138篇
  免费   4635篇
  国内免费   1042篇
电工技术   8404篇
综合类   415篇
化学工业   71328篇
金属工艺   23226篇
机械仪表   16636篇
建筑科学   9769篇
矿业工程   4446篇
能源动力   9689篇
轻工业   30906篇
水利工程   6139篇
石油天然气   14912篇
武器工业   91篇
无线电   50610篇
一般工业技术   103659篇
冶金工业   73485篇
原子能技术   14674篇
自动化技术   37426篇
  2021年   4202篇
  2019年   4170篇
  2018年   7790篇
  2017年   8074篇
  2016年   8527篇
  2015年   4819篇
  2014年   8340篇
  2013年   19640篇
  2012年   12516篇
  2011年   16306篇
  2010年   13062篇
  2009年   14607篇
  2008年   15459篇
  2007年   15172篇
  2006年   13045篇
  2005年   11762篇
  2004年   11417篇
  2003年   11207篇
  2002年   10721篇
  2001年   10625篇
  2000年   10345篇
  1999年   9858篇
  1998年   20264篇
  1997年   15245篇
  1996年   11927篇
  1995年   9554篇
  1994年   8669篇
  1993年   8724篇
  1992年   7274篇
  1991年   7080篇
  1990年   7037篇
  1989年   6716篇
  1988年   6448篇
  1987年   6028篇
  1986年   5878篇
  1985年   6486篇
  1984年   6220篇
  1983年   5755篇
  1982年   5454篇
  1981年   5568篇
  1980年   5406篇
  1979年   5486篇
  1978年   5542篇
  1977年   5910篇
  1976年   6958篇
  1975年   5106篇
  1974年   5147篇
  1973年   5229篇
  1972年   4467篇
  1971年   4109篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
951.
With the aim of optimizing the performance of Li/Li1+xV3O8 cells, several aspects of cathode preparation have been examined. The influence of synthesis technique, nature and amount of conductive additives, compacting pressure, cathode loading, and particle size, has been investigated. Furthermore, the role played by the solutions on cathode efficiency has been outlined. The formulations which perform best are based on small-sized particles blended with about 20% acetylene black and compacted at very high pressures to improve the contact between particles. Such cathodes can provide high capacities at high rates and good cycling efficiencies. The kinetic loss of capacity, observed during the first few cycles, may be alleviated by choosing solutions with high fluidity and conductivity.  相似文献   
952.
Salmonella strains exposed to lethal doses of gamma radiation are detoxified but retain their antigenic properties. Using eight Salmonella strains representative of each of the Salmonella serogroups A to G, a polyvalent radiovaccine has been developed which effectively immunizes mice to several Salmonella serotypes.  相似文献   
953.
Smoke-haze episodes caused by vegetation and peat fires affect parts of Indonesia every year with significant impacts on human health and climate. The forest fires 1997/1998 were by far the largest in Indonesian history, burning between 5 and 8 million hectares before they were stopped by the monsoon rains in December 1997. Fires sprang up again in 1998 on Kalimantan when monsoon rain paused. Peat forests and peatlands are in particular severely affected. In the 1997/1998 haze event, 2.1-2.5 million hectare of peat swamp forest burnt in Indonesia. The remaining ash contains high concentrations of sulphur and sulphuric compounds which eventually leach into the groundwater, thus polluting groundwater and drinking water. The thicker the peat layer is and the higher the number of fires in the respective area the more sulphuric compounds will leach into the groundwater. Risk areas for the sulphur loads of the ash are identified.  相似文献   
954.
A contact probe test was developed to characterize the surface stickiness of a tomato pulp droplet at various moisture contents and temperatures. To provide tomato pulp samples with different moisture contents, tomato powder produced by a laboratory spray dryer was wetted to seven different moisture levels. The instantaneous tensile force curve was recorded during the probe withdrawal from which the maximum tensile force and other useful information were obtained and cross-examined against images of bonding, debonding, and failure of the material. Generally, at higher moisture contents tomato pulp exhibited cohesive failure followed by semi-adhesive failure, but when moisture content decreased to a certain level, a peak tensile pressure was observed and the failure was adhesive. In addition, higher temperatures shifted the points of adhesive failure toward lower moisture content.  相似文献   
955.
Phytic acid-rich particles were isolated from a combined density fraction (CDF) of Great Northern beans. CDF contained more than 80% of the total phytic acid, and 70% of the total crude protein and substantial amounts of certain minerals. CDF had phytic acid in both water soluble and water insoluble forms. An isolate containing phytic acid-rich particles was prepared from CDF using a Tris-base solution. The phytic acid-rich isolate contained 26.6% phytic acid, 34.3% protein, 30.0% total carbohydrates, 0.6% calcium, 2.1% magnesium, and 0.3% potassium. Chemical analysis and fractionation of CDF indicated that the water insoluble form of phytic acid in Great Northern beans was present as a salt of calcium-magnesium-potassium in association with proteins.  相似文献   
956.
A method for predicting the long-term performance of solar energy systems, based on the analysis of system performance for one particular day—the typical meteorological day (TMD)—is presented. The TMD is constructed from the cumulative time distribution of insolation values on the collector aperture. The TMD method requires little calculational effort and a small data base relative to standard yearly computer simulations. Good agreement is found between the predictions of the new method and the corresponding results of the -f-chart method. The TMD method is of particular value for cases that may often be treated inaccurately by simple calculational methods: (1) high threshold problems; (2) systems with short response times (e.g., due to small storage); and (3) systems in which collectors other than flat plates are used (the method is applicable to all solar collector types).  相似文献   
957.
958.
Estrogenic personal care products in a greywater reuse system.   总被引:1,自引:0,他引:1  
The occurrence and fate of parabens in a greywater system was assessed. The potential for removal of residual paraben concentrations in effluent greywater with chlorine dioxide was also investigated. The influent to the greywater plant was characterised by considerable variation, with concentrations from below the detection limit to 40 microg/L and the five commonly used parabens in consumer products were frequently detected. After the biological treatment only two paraben were detected with concentration from 65-120 ng/L. Chlorine dioxide treatment of the biologically treated effluent with dosages down to 0.75 mg/L resulted in more than 97% reduction of all parabens. Formation of the by-product chloroform was insignificant from the chlorine dioxide treatment.  相似文献   
959.
This is a review paper addressing the current state-of-the-art. Concerns that motivate studies of the indoor environment are reviewed in the introduction. The source and typical diurnal variations of the concentration of several air contaminants are discussed in the section on characterization. A dynamic model is described in the section on indoor air quality modeling. Indoor air pollution control techniques are addressed in the last section.  相似文献   
960.
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