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   11431篇
  免费   760篇
  国内免费   270篇
电工技术   162篇
综合类   650篇
化学工业   4760篇
金属工艺   563篇
机械仪表   123篇
建筑科学   206篇
矿业工程   446篇
能源动力   141篇
轻工业   2484篇
水利工程   41篇
石油天然气   475篇
武器工业   17篇
无线电   357篇
一般工业技术   1099篇
冶金工业   605篇
原子能技术   293篇
自动化技术   39篇
  2025年   68篇
  2024年   269篇
  2023年   245篇
  2022年   346篇
  2021年   397篇
  2020年   477篇
  2019年   446篇
  2018年   374篇
  2017年   447篇
  2016年   470篇
  2015年   393篇
  2014年   585篇
  2013年   738篇
  2012年   791篇
  2011年   735篇
  2010年   500篇
  2009年   493篇
  2008年   423篇
  2007年   551篇
  2006年   569篇
  2005年   476篇
  2004年   410篇
  2003年   339篇
  2002年   331篇
  2001年   276篇
  2000年   254篇
  1999年   211篇
  1998年   159篇
  1997年   126篇
  1996年   98篇
  1995年   81篇
  1994年   66篇
  1993年   65篇
  1992年   52篇
  1991年   42篇
  1990年   30篇
  1989年   21篇
  1988年   18篇
  1987年   9篇
  1986年   9篇
  1985年   16篇
  1984年   10篇
  1983年   11篇
  1982年   9篇
  1981年   2篇
  1980年   9篇
  1979年   4篇
  1976年   2篇
  1959年   4篇
  1951年   2篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Investigation of the effects of varying air velocity, slice thickness, and pre-treatment with sodium chloride solutions and surface active agents on drying potato slices indicated that the drying occurred entirely in the falling rate period and was controlled by the mechanism of liquid diffusion. The rate of drying, and therefore the diffusion coefficients, increased with the addition of sodium chloride and surface active agents. Diffusion coefficients were also influenced by air velocity and slice thickness, suggesting that the rate of drying of potato slices is controlled by a combination of internal and external resistances.  相似文献   
2.
The influence of NaCl and CO2 on the atmospheric corrosion of magnesium alloy AZ91 is studied in the laboratory. Samples were exposed under carefully controlled air and flow conditions; the relative humidity was 95%, the temperature was 22.0°C and the concentration of CO2 was < 1 ppm or 350 ppm. Different amounts of sodium chloride (0–70 μg/cm2) were added before exposure. The corrosion products were analyzed by gravimetry, ion chromatography, X‐ray diffraction and scanning electron microscopy. Mass gain and metal loss results are reported. The combination of high humidity and NaCl is very corrosive towards AZ91. However, the NaCl‐induced corrosion is inhibited by ambient concentrations of CO2. Exposure in the absence of CO2 gives rise to heavy pitting, with brucite, Mg(OH)2, being the dominant corrosion product. In the presence of CO2 a layer of hydrated magnesium hydroxy carbonate, Mg5(CO3)4(OH)2 · 5 H2O forms. A tentative corrosion mechanism is presented that explains the behavior in the two environments.  相似文献   
3.
Polysaccharide was isolated from Cordia abyssinica and its effect, at differing concentrations, on its emulsifying ability was determined. Emulsions of vegetable oil containing up to 1% of the polysaccharide in phosphate pH 7.4 buffer, were prepared by using a hand piston homogenizer. Emulsification was assessed by diluting samples of the emulsions in sodium dodecyl sulphate and measuring absorbance at 500 nm. Addition of increasing concentrations of the polysaccharide up to 1% enhanced emulsification and emulsion stability. Above 1% concentration the polysaccharide solutions were too viscous for making emulsions conveniently. At a constant concentration of the polysaccharide, addition of up to a 1% concentration of salt enhanced emulsion formation. Further addition of salt above 1% resulted in no further changes in emulsifying ability, but the stability of the emulsions formed decreased on increasing the concentration of salt above 1%. The effect of pH on emulsifying ability was investigated by preparing emulsions using buffers of different pH, from pH 3 to pH 13. The polysaccharide had poor emulsifying ability below pH 7. Emulsifying ability increased with pH between pH 7 and 11. At pH above 11 there was a decrease in emulsifying ability.  相似文献   
4.
用共沉淀法制备Fe3O4磁流体,总结出用十二烷基磺酸钠与聚乙二醇作为表面活性剂制备水基磁流体的合适条件:(1)反应温度为室温或不高于35℃;(2)表面活性剂十二烷基磺酸钠的最佳用量为0.0030~0.0040 g/80 mL;(3)第一次包裹的最佳pH为9~10;(4)聚乙二醇作为第二次包裹的表面活剂时,体系最佳温度为40℃左右;(5)表面活性剂聚乙二醇的最佳用量为0.0050~0.0060 g/80 mL。通过实验制得了能稳定存在180 d的水基磁流体。并用透射电镜、红外光谱、分光光度计、古埃磁天平等进行了初步表征。  相似文献   
5.
采用铝酸钠种子分解法制备超细Al(OH)3.用X射线衍射仪(XRD)表征了样品的晶相组成,用扫描电子显微镜(SEM)观察了样品的形貌,用激光粒度分析仪测定样品的粒度分布.研究了NaOH浓度、NaOH/Al(OH)3摩尔比,分解温度,分解时间、晶种率和搅拌速率等因素对Al(OH)3的粒度的影响.结果表明:NaOH浓度越高,分解温度越低,NaOH/Al(OH)3摩尔比越小,得到的Al(OH)3颗粒的粒度越小.试验条件为:NaOH浓度180 g/L,NaOH/Al(OH)3摩尔比1.15,分解温度40℃,分解时间26 h,晶种率8%,搅拌速率200 rpm时,氢氧化铝颗粒的平均粒度为2.89 μm.  相似文献   
6.
过硼酸钠在有机合成中的应用   总被引:1,自引:0,他引:1  
李润涛  杨锦宗 《化学试剂》1995,17(2):95-100
过硼酸钠(SPB)是一种安全、稳定、方便、价廉的理想氧化剂,本文综述了它对各类有机化合物的氧化反应。  相似文献   
7.
Objective: The aim of this study was to prepare pH-sensitive sodium alginate/calcined hydrotalcite (SA/CHT) hybrid bead with improved the burst release effect of the drug.

Materials and methods: A series of pH-sensitive SA/CHT hybrid beads were prepared by using Ca2+ cross-linking in the presence of diclofenac sodium (DS) and SA. The structure and drug loading of the beads were characterized by Fourier transform infrared spectroscopy and X-ray diffraction. The swelling and the drug release of the fabricated beads were investigated by the pH of test medium and CHT content.

Result: The formed positively charged hydrotalcite layers were adsorbed on the negatively charged SA polymer chains through electrostatic interaction and act as inorganic cross-linkers in the three-dimensional network. Compared to pure SA beads, the incorporation of CHT enhanced the drug encapsulation efficiency, improved the swelling behaviors and slowed the drug release from the hybrid beads.

Discussion and conclusions: The electrostatic interaction between hydrotalcite and SA has restricted the movability of the SA polymer chains, and then slowed down swelling and dissolution rates in aqueous solutions. The results provided a simple method to moderate drug release and matrix degradation of the SA beads.  相似文献   
8.
四苯硼钠比浊界限分析法测钾   总被引:2,自引:0,他引:2  
试样经掩蔽铁杂质后,在微酸性条件下用四苯硼钠沉淀钾离子再与钾标准进行比浊,该方法便捷,测定范围为≥0.4≤1.2g/1KClO3。  相似文献   
9.
10.
详细分析了硫酸铜浓度对过硫酸钠体系微蚀速率的影响,并对其机理进行了探讨。  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