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   25605篇
  免费   3257篇
  国内免费   1962篇
电工技术   3066篇
综合类   3023篇
化学工业   2378篇
金属工艺   1879篇
机械仪表   2005篇
建筑科学   1965篇
矿业工程   607篇
能源动力   700篇
轻工业   1139篇
水利工程   586篇
石油天然气   1594篇
武器工业   338篇
无线电   2723篇
一般工业技术   2567篇
冶金工业   1064篇
原子能技术   221篇
自动化技术   4969篇
  2024年   74篇
  2023年   458篇
  2022年   815篇
  2021年   995篇
  2020年   1005篇
  2019年   762篇
  2018年   679篇
  2017年   896篇
  2016年   1001篇
  2015年   1054篇
  2014年   1688篇
  2013年   1661篇
  2012年   1996篇
  2011年   2002篇
  2010年   1541篇
  2009年   1572篇
  2008年   1424篇
  2007年   1721篇
  2006年   1488篇
  2005年   1254篇
  2004年   1059篇
  2003年   934篇
  2002年   832篇
  2001年   660篇
  2000年   593篇
  1999年   445篇
  1998年   362篇
  1997年   331篇
  1996年   260篇
  1995年   239篇
  1994年   208篇
  1993年   171篇
  1992年   160篇
  1991年   101篇
  1990年   75篇
  1989年   84篇
  1988年   50篇
  1987年   28篇
  1986年   23篇
  1985年   20篇
  1984年   22篇
  1983年   20篇
  1982年   11篇
  1981年   7篇
  1980年   10篇
  1979年   6篇
  1978年   4篇
  1976年   4篇
  1975年   4篇
  1962年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
Ternary 0.552Pb(Ni1/3Nb2/3)O3-xPbZrO3-(0.448-x)PbTiO3 (PNN-PZ-PT) ceramics near the triple point compositions were fabricated by an improved two-step sintering method. The triple point composition 0.552PNN-0.135PZ-0.313PT ceramic has outstanding piezoelectric performance with piezoelectric coefficient d33 = 1200 pC/N. Its easy fabrication and low cost make this piezoelectric material an excellent candidate for high sensitivity sensors and ultrasonic transducers. The evolution of domain structures for ceramics with composition near the triple point provides deeper insight into the mechanism of ultrahigh piezoelectric properties of PNN-PZ-PT ceramics.  相似文献   
104.
105.
蔡璋 《铜业工程》2022,(4):73-76
采用三维激光扫描非接触倾斜测量法,可以高效获取矿仓中精矿产品的物料堆积形态。通过优化精矿盘点扫描测量流程,精准计算出矿仓库存量,提高了精矿盘点数据的准确性、测量的高效性和操作的安全性。  相似文献   
106.
Sisal (Agave sisalana) is the main hard fiber produced worldwide, with an estimated generation of 400 thousands t in 2011. From its leaves, only the hard fibers, which represent 3–5% of their weight, are removed. The remaining 95–97% is referred to as sisal waste and contains steroidal saponins that can be potentially used in foods, cosmetics and pharmaceuticals formulations, as well as for soil bioremediation. The present work aimed at to evaluate strategies for the extraction and concentration of saponins from sisal waste, focused on the use of clean solvents, such as water and ethanol. For this purpose, it was firstly performed a central composite rotatable design for the optimization of the extraction conditions followed by a comparison of this strategy with other methods (Soxhlet, ultrasound-assisted extraction and micellar extraction). Cloud point preconcentration was then tested, using several types and concentrations of salts. The use of orbital shaker extraction (200 rpm) with an ethanolic solution (30%, v/v) at 50 °C, a mass/volume ratio sisal/solvent of 0.17 (g/mL) for 4 h allowed a recovery of 38.6% of the saponins. When a micellar extraction strategy using 7.5% (v/v) of Triton X-100, under the above-mentioned conditions was performed, saponins recovery raised to 98.4%. In a subsequent step, the addition of 20% (m/v) sodium carbonate led to a preconcentration factor of 20.3. The best adsorbent for Triton removal from the preconcentrated solution was Amberlite FPX-66. The process strategy proposed in the present study showed to be efficient for saponins extraction and preconcentration from a low-cost, highly available agricultural waste.  相似文献   
107.
The 9‐point hedonic scale has been used routinely in food science, the same way for 60 years. Now, with advances in technology, data from the scale are being used for more and more complex programs for statistical analysis and modeling. Accordingly, it is worth reconsidering the presentation protocols and the analyses associated with the scale, as well as some alternatives. How the brain generates numbers and the types of numbers it generates has relevance for the choice of measurement protocols. There are alternatives to the generally used serial monadic protocol, which can be more suitable. Traditionally, the ‘words’ on the 9‐point hedonic scale are reassigned as ‘numbers’, while other ‘9‐point hedonic scales’ are purely numerical; the two are not interchangeable. Parametric statistical analysis of scaling data is examined critically and alternatives discussed. The potential of a promising alternative to scaling itself, simple ranking with a hedonic R‐Index signal detection analysis, is explored in comparison with the 9‐point hedonic scale. © 2014 Society of Chemical Industry  相似文献   
108.
结合某年产20万t乙二醇项目,分析220t/h高温高压低倍率循环流化床燃煤锅炉温度测点的布置。通过对比各种温度检测仪表的优、缺点,并分析温度测点处介质的特点,给出了安化220t/h循环流化床锅炉温度仪表的选型方案。  相似文献   
109.
The effect of drying air temperature on the mechanical properties of corn kernels was investigated. Corn was dried at drying temperatures of 40, 50, 60 and 70°C and air flow rate of 1.8 kg/min in a convective dryer. The kernels were then loaded uniaxially in a material testing machine at a loading rate of 3 mm/min, up to the rupture point. An increase in drying temperature from 40 to 70°C increased kernel deformation at the rupture point by an average of 12%. Moreover, values of force, stress, toughness, and modulus of elasticity of corn decreased on average by 21, 26, 36, and 38%, respectively.  相似文献   
110.
The objective of this study was to analyze the influence of the presence of activated carbon on the degradation of the triiodinated contrast medium diatrizoate (DTZ) by the simultaneous use of gamma radiation and activated carbon. Four commercial activated carbons (Ceca, Witco, Sorbo, and Merck) with different textural and chemical characteristics were used for this purpose. The percentage DTZ removal obtained was considerably higher with the gamma radiation/activated carbon (GM/AC) system than with radiolysis in the absence of activated carbon, and it depended on the specific activated carbon employed. First, we optimized the amount of activated carbon required to maximize the amount of DTZ removed by the GM/AC system (0.06 g). The degradation constants were higher with the GM/AC system than with radiolysis alone, evidencing a synergic effect that favors pollutant removal. This synergic effect is independent of the textural but not the chemical characteristics of the activated carbon, observing a higher synergic activity for carbons with a higher surface content of oxygen, specifically quinone groups. We also highlight that the synergic effect of the activated carbon requires adsorbent–adsorbate electrostatic interaction and is absent when this interaction is hindered.  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