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   73042篇
  免费   4293篇
  国内免费   1064篇
电工技术   1765篇
技术理论   2篇
综合类   1548篇
化学工业   13744篇
金属工艺   2890篇
机械仪表   3977篇
建筑科学   2471篇
矿业工程   537篇
能源动力   2528篇
轻工业   6046篇
水利工程   570篇
石油天然气   965篇
武器工业   132篇
无线电   11569篇
一般工业技术   13096篇
冶金工业   6579篇
原子能技术   886篇
自动化技术   9094篇
  2024年   97篇
  2023年   767篇
  2022年   1296篇
  2021年   1949篇
  2020年   1423篇
  2019年   1398篇
  2018年   1752篇
  2017年   1819篇
  2016年   2110篇
  2015年   1930篇
  2014年   2901篇
  2013年   4570篇
  2012年   4319篇
  2011年   5174篇
  2010年   4132篇
  2009年   4284篇
  2008年   4067篇
  2007年   3517篇
  2006年   3237篇
  2005年   2775篇
  2004年   2497篇
  2003年   2259篇
  2002年   2243篇
  2001年   1779篇
  2000年   1597篇
  1999年   1505篇
  1998年   2390篇
  1997年   1603篇
  1996年   1361篇
  1995年   1095篇
  1994年   834篇
  1993年   755篇
  1992年   561篇
  1991年   542篇
  1990年   452篇
  1989年   432篇
  1988年   350篇
  1987年   291篇
  1986年   269篇
  1985年   249篇
  1984年   210篇
  1983年   157篇
  1982年   157篇
  1981年   136篇
  1980年   133篇
  1979年   109篇
  1978年   97篇
  1977年   127篇
  1976年   165篇
  1975年   81篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
921.
Four temporarily solubilised azo disperse dyes based on 1-substituted-2-hydroxypyrid-6-one were synthesised and characterised. The dyes showed high extinction coefficients and had a yellow shade on polyester fabric. They were successfully applied to polyester without the use of dispersants and the optimum pH was found to be 5. It was found that the dyes could be alkali-cleared due to ionisation of the dye under mild alkaline conditions. The dyes exhibited good to excellent fastness properties on the polyester fabric.  相似文献   
922.
Gas hydrate formation experiments were conducted with a methane-ethane mixture at 273.7 or 273.9 K and 5100 kPa and using water droplets or water contained in cylindrical glass columns. The effect of kinetic inhibitors and the water/solid interface on the induction time for hydrate crystallization and on the hydrate growth and decomposition characteristics was studied. It was found that inhibitors GHI 101 and Luvicap EG delayed the onset of hydrate nucleation. While this inhibition effects has been reported previously some unusual behaviour was observed and reported for the first time. In particular, the water droplet containing GHI 101 or Luvicap EG was found to collapse prior to nucleation and spread out on the Teflon surface. Subsequently, hydrate was formed as a layer on the surface. Catastrophic growth and spreading of the hydrate crystals was also observed during hydrate formation in the glass columns in the presence of the kinetic inhibitor. Finally, when polyethylene oxide (PEO) was added into the kinetic inhibitor solution the memory effect on the induction time decreased dramatically.  相似文献   
923.
填料并用对双组分室温硫化导热硅橡胶性能的影响   总被引:9,自引:2,他引:9  
以α,ω-二羟基聚二甲基硅氧烷为基胶,Si3N4、AlN、Al2O3为导热填料,制备了填充型双组分室温硫化(RTV-2)导热硅橡胶.研究了填料Si3N4/Al2O3或AlN/Al2O3并用对RTV-2硅橡胶导热性能、工艺性能及力学性能的影响.结果表明,当填料的总体积分数为0.45时,对于Si3N4/Al2O3填充体系,随着体系中Al2O3体积分数的增加,RTV-2导热硅橡胶的热导率先升后降、拉伸强度先增后减,而扯断伸长率则呈逐渐升高的趋势,基料的粘度先减后增;当Al2O3的体积分数为0.14时,RTV-2导热硅橡胶的热导率最高、拉伸强度最大,基料的粘度最小,综合性能最佳.对于AlN/Al2O3填充体系,随着体系中Al2O3的体积分数的增加,RTV-2导热硅橡胶的热导率先升后降、拉伸强度及扯断伸长率先减后增,基料的粘度呈上升趋势;当Al2O3的体积分数为0.07时,RTV-2导热硅橡胶具有较好的导热性能和工艺性能,但力学性能偏低.  相似文献   
924.
Although carbon fiber epoxy composite materials have excellent properties for structures, the joint in composite materials often reduces the efficiency of the composite structure because the joint is often the weakest area in the composite structure.

In this paper, the effects of the adhesive thickness and the adherend surface roughness on the static and fatigue strengths of adhesively-bonded tubular polygonal lap joints have been investigated by experimental methods. The dependencies of the static and fatigue strengths on the stacking sequences of the composite adherends were observed.

From the experimental investigations, it was found that the fatigue strength of the circular adhesively-bounded joints was quite dependent on the surface roughness of the adherends and that polygonal adhesively-bonded joints had better fatigue strength characteristics than circular adhesively-bonded joints.  相似文献   
925.
The synergistic effects of boron nitride (BN) powder and die on the rheology and processability of metallocene‐catalyzed low density polyethylene (mLDPE) were investigated. The processability in the extrusion process is closely related to the interfacial properties between the polymer melts and the die wall. BN powder was added to mLDPE to reduce the friction coefficient and surface energy. Adding 0.5 wt% BN powder to mLDPE was very effective in improving the processability and the extrudate appearance. To study the effect of die surface property, three different dies were applied in capillary extrusion. One was conventional tungsten carbide (TC) die, and the others were hot‐pressed BN (hpBN) die and hot‐pressed BN composite (hpBNC) die. The applications of these BN dies were quite effective in delaying surface melt fracture (sharkskin) and postponing gross melt fracture to higher shear rate compared to the TC die. These improvements result from the fact that BN dies reduce the wall shear stress significantly and promote slip. The synergistic effect of processability could be obtained when both BN powder and hpBN die were used together.  相似文献   
926.
以Ti,Al,C微粉为原料,分别采用放电等离子(SPS)烧结工艺和热压工艺(HP)烧结制备Ti2AlC层状陶瓷材料。X射线衍射和扫描电镜(SEM)分析的结果表明:采用放电等离子(SPS)烧结工艺时,能够在1100℃的温度下制备高纯、致密Ti2AlC材料。采用热压工艺时,则很难合成高纯的Ti2AlC陶瓷材料。  相似文献   
927.
Ionic liquids are compounds that composed only of ions and are liquid at room temperature. Thus, it is normally named room temperature ionic liquid (RTIL). In this study, the application of RTILs to the extractive fermentation of biomaterials was investigated as a substitute of organic solvents. The relative toxicity of the RTILs on the growth ofE. coli was tested. The inhibition of cell growth in the presence of various ionic liquids was measured using solid and liquid culture, and EC50 of each RTILs was calculated. The number of viable and total cells was measured by the number of colonies and optical density, respectively. Effective concentrations of toxicity (EC50) in these tested systems were similar with conventional solvents, such as acetone, acetonitrile, and ethanol. The viability ofE. coli was affected by the polarity and ionic properties of ionic liquids. The resistance of the microorganisms against ionic liquids was different with the cations and anions composing ionic liquids. No general influence of the anionic compound of the ionic liquids was found on toxicity comparing with distinctive influence of cationic moiety.  相似文献   
928.
磺草酮对玉米的安全性及除草效果评价   总被引:2,自引:1,他引:2  
田间测定了磺草酮对玉米的安全性及防除杂草试验效果,结果表明磺草酮有效成分562.5~1200g/hm^2防除玉米田单子叶杂草马唐、牛筋草、狗尾草效果较好,防效为86.5%~98.0%;对双子叶杂草中的反枝苋防效较好,防效为99.3%~l00%;对铁苋莱和马齿苋防效较差,防效为35.0%~62.9%。对玉米有触杀性药害,至药后15天药害症状消失,不影响玉米的产量,且有较好的增产作用,增产l0.0%左右。  相似文献   
929.
某星载天线复合材料骨架的动态特性   总被引:2,自引:0,他引:2  
本文介绍了纤维缠绕复合材料壳体的刚度的计算方法,采用有限元工程分析软件ANSYS对某星载雷达碳纤维缠绕复合材料天线骨架结构的动态特性进行了分析和计算,所得结果为天线结构设计提供了参考依据。  相似文献   
930.
Eddy characteristics on mass transfer close to free interface   总被引:1,自引:0,他引:1  
The velocity fluctuations in the immediate vicinity of a free interface were measured with a hot film anemometer. And mass transfer rates and eddy exposure times were analyzed by using the method of deterministic approach. These mass transfer rates were compared with the mass transfer rates by means of concentration measurements in the air-water system. The eddy exposure time distributions obtained from velocity data were skewed toward the lower time value. The contribution of eddies wi:h small exposure time was increased as the liquid became more turbulent. The mass transfer rates were mainly contributed by the Prandtl size eddies and even larger eddies. The mass transfer predictions by the single eddy model employing a deterministic method were in good agreement with the experimental results by independent measurements of concentration.  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