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   2077篇
  免费   15篇
  国内免费   11篇
电工技术   12篇
综合类   2篇
化学工业   161篇
金属工艺   8篇
机械仪表   19篇
建筑科学   16篇
能源动力   35篇
轻工业   27篇
水利工程   6篇
石油天然气   3篇
无线电   106篇
一般工业技术   131篇
冶金工业   1485篇
原子能技术   7篇
自动化技术   85篇
  2024年   3篇
  2023年   5篇
  2022年   25篇
  2021年   33篇
  2020年   27篇
  2019年   32篇
  2018年   34篇
  2017年   25篇
  2016年   22篇
  2015年   17篇
  2014年   14篇
  2013年   52篇
  2012年   33篇
  2011年   37篇
  2010年   25篇
  2009年   32篇
  2008年   24篇
  2007年   13篇
  2006年   12篇
  2005年   22篇
  2004年   21篇
  2003年   17篇
  2002年   6篇
  2001年   5篇
  2000年   3篇
  1999年   58篇
  1998年   459篇
  1997年   260篇
  1996年   187篇
  1995年   81篇
  1994年   87篇
  1993年   82篇
  1992年   14篇
  1991年   19篇
  1990年   27篇
  1989年   30篇
  1988年   21篇
  1987年   18篇
  1986年   23篇
  1985年   18篇
  1984年   7篇
  1983年   2篇
  1982年   5篇
  1981年   9篇
  1980年   19篇
  1978年   6篇
  1977年   38篇
  1976年   82篇
  1975年   5篇
  1970年   3篇
排序方式: 共有2103条查询结果,搜索用时 31 毫秒
971.
Coastal water issues are gaining worldwide attention because of their impact on health and other environmental problems. This article is concerned with the comparison between artificial neural networks and statistical methods to predict the degree of acidity (pH) in the coastal waters along the Gaza beach. Multilayer perceptron (MLP) and radial basis function (RBF) neural networks are trained and developed with reference to three parameters (water temperature, wind velocity, and turbidity) to predict the level of pH in the seawater. Both networks were developed using the combination of the data collected from nine sites over a period of 4 years, including 294 samples for training and 90 samples for testing the performance of models. The results show that the MLP and RBF models have good ability to predict the pH level. Each network's performance was tested with different sets of data, and the results show satisfactory performance. Results of the developed networks were compared with the statistical regression method and found that the predictions of neural networks are better than the conventional methods. Predictions result show that artificial neural networks approach have good ability for the modeling of pH level in the coastal waters along Gaza beach. It is hoped that neural networks will prove to be a promising alternative to traditional methods used and can contribute in the improvement of the quality of seawater.  相似文献   
972.
Electroless nickel–phosphorus (ENi–P) coating was carried out on AZ91 magnesium alloy substrates by varying the bath solutions pH. The ENi–P coating process was carried out with sodium hydroxide as the pH adjuster. The effect of bath pH values on surface characteristics and wear resistance properties were investigated after deposition on AZ91 magnesium alloy substrates. Three suitable bath compositions with different pH were prepared for coating the substrates. Encouraging results for ENi–P deposit were obtained when the bath pH value was maintained at 6.5. A smooth and uniform microstructure was observed in the deposit obtained from bath B (6.5 pH). It also enhanced the microhardness and wettability, while the surface roughness of the ENi–P deposit reduced considerably, thereby resulting in better wear resistance and also preventing regular or early failures, and improving service life.  相似文献   
973.
The electrical conductivity, thermoelectric power and dielectric constant of Eu2Ti2O7 single crystal have been studied in the temperature range 300–1000 K. Eu2Ti2O7 is found to be a n-type semiconductor with energy band gap of 2.5 eV. The compound exhibits an extrinsic nature upto 700 K and intrinsic nature above 700 K. Thermoelectric power decreases with temperature in the region 300–700 K whereas it increases with temperature in the region 700–1000 K. Dielectric constant increases with temperature in the entire temperature range studied with a discontinuity atT 700 K.  相似文献   
974.
The influence of selected long-chain FA hydrazides and thiosemicarbazides on the corrosion inhibition of mild steel in the presence of 20% formic acid was studied. The inhibition efficiency of these compounds varied with concentration, temperature, and immersion time. All the FA derivatives in the formic acid solution followed Temkin's adsorption isotherm. The activation energies and free energies of adsorption of all the hydrazides and thiosemicarbazides also were calculated. Potentiodynamic polarization studies indicated that all the tested compounds were of mixed type. Electrochemical impedance spectroscopy was also used to investigate the mechanism of corrosion inhibition.  相似文献   
975.
Polymers are fast replacing the conventional building materials, mainly because of their scarcity and attractive properties. However, users are hesitant to accept these alternate building materials as the polymers are considered to be associated with fire hazards. Red mud plastics (RMP) is one such polymer which is finding acceptance albeit slowly. Fire behaviour of RMP is discussed and compared with some conventional materials with a view to present it as a viable alternate.  相似文献   
976.
In this work, adsorption of copper (Cu), zinc (Zn), lead (Pb), and cadmium (Cd) that exist in industrial wastewater onto the carbon produced from nutshells of walnut, hazelnut, pistachio, almond, and apricot stone has been investigated. All the agricultural shell or stone used were ground, sieved to a defined size range, and carbonized in an oven. Time and temperature of heating were optimized at 15 min and 800 degrees C, respectively, to reach maximum removal efficiency. Removal efficiency was optimized regarding to the initial pH, flow rate, and dose of adsorbent. The maximum removal occurred at pH 6-10, flow rate of 3 mL/min, and 0.1g of the adsorbent. Capacity of carbon sources for removing cations will be considerably decreased in the following times of passing through them. Results showed that the cations studied significantly can be removed by the carbon sources. Efficiency of carbon to remove the cations from real wastewater produced by copper industries was also studied. Finding showed that not only these cations can be removed considerably by the carbon sources noted above, but also removing efficiency are much more in the real samples. These results were in adoption to those obtained by standard mixture synthetic wastewater.  相似文献   
977.
978.
979.
980.
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