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   86842篇
  免费   6496篇
  国内免费   2926篇
电工技术   4180篇
技术理论   9篇
综合类   4501篇
化学工业   14728篇
金属工艺   4668篇
机械仪表   4871篇
建筑科学   5407篇
矿业工程   2458篇
能源动力   2851篇
轻工业   5897篇
水利工程   1300篇
石油天然气   4657篇
武器工业   540篇
无线电   11042篇
一般工业技术   11306篇
冶金工业   5618篇
原子能技术   1029篇
自动化技术   11202篇
  2024年   161篇
  2023年   1258篇
  2022年   1918篇
  2021年   3301篇
  2020年   2524篇
  2019年   2172篇
  2018年   2483篇
  2017年   2661篇
  2016年   2402篇
  2015年   3112篇
  2014年   4060篇
  2013年   5182篇
  2012年   5264篇
  2011年   5882篇
  2010年   5004篇
  2009年   4719篇
  2008年   4713篇
  2007年   4451篇
  2006年   4443篇
  2005年   3710篇
  2004年   2647篇
  2003年   2536篇
  2002年   2666篇
  2001年   2171篇
  2000年   2004篇
  1999年   2177篇
  1998年   2142篇
  1997年   1682篇
  1996年   1526篇
  1995年   1334篇
  1994年   1079篇
  1993年   781篇
  1992年   603篇
  1991年   506篇
  1990年   459篇
  1989年   392篇
  1988年   339篇
  1987年   250篇
  1986年   212篇
  1985年   182篇
  1984年   158篇
  1983年   105篇
  1982年   101篇
  1981年   88篇
  1980年   98篇
  1979年   56篇
  1978年   67篇
  1977年   68篇
  1976年   90篇
  1975年   47篇
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
21.
Sensitivity and multi-directional motivation are major two factors for developing optimized humidity-response materials, which are promising for sensing, energy production, etc. Organic functional groups are commonly used as the water sensitive units through hydrogen bond interactions with water molecules in actuators. The multi-coordination ability of inorganic ions implies that the inorganic ionic compounds are potentially superior water sensitive units. However, the particle forms of inorganic ionic compounds produced by classical nucleation limit the number of exposed ions to interact with water. Recent progress on the inorganic ionic oligomers has broken through the limitation of classical nucleation, and realized the molecular-scaled incorporation of inorganic ionic compounds into an organic matrix. Here, the incorporation of hydrophilic calcium carbonate ionic oligomers into hydrophobic poly(vinylidene fluoride) (PVDF) is demonstrated. The ultra-small calcium carbonate oligomers within a PVDF film endow it with an ultra-sensitive, reversible, and bidirectional response. The motivation ability is superior to other bidirectional humidity-actuators at present, which realizes self-motivation on an ice surface, converting the chemical potential energy of the humidity gradient from ice to kinetic energy.  相似文献   
22.
Ce:Y3Al5O12 transparent ceramics (TCs) with appropriate emission light proportion and high thermal stability are significant to construct white light emitting diode devices with excellent chromaticity parameters. In this work, strategies of controlling crystal-field splitting around Ce3+ ion and doping orange-red emitting ion, were adopted to fabricate Ce:(Y,Tb)3(Al,Mn)5O12 TCs via vacuum sintering technique. Notably, 85.4 % of the room-temperature luminescence intensity of the TC was retained at 150 °C, and the color rendering index was as high as 79.8. Furthermore, a 12 nm red shift and a 16.2 % increase of full width at half maximum were achieved owing to the synergistic effects of Tb3+ and Mn2+ ions. By combining TCs with a 460 nm blue chip, a warm white light with a low correlated color temperature of 4155 K was acquired. Meanwhile, the action mechanism of Tb3+ ion and the energy transfer between Ce3+ and Mn2+ ions were verified in prepared TCs.  相似文献   
23.
The germline carrier of the BRCA1 pathogenic mutation has been well proven to confer an increased risk of breast and ovarian cancer. Despite BRCA1 biallelic pathogenic mutations being extremely rare, they have been reported to be embryonically lethal or to cause Fanconi anemia (FA). Here we describe a patient who was a 48-year-old female identified with biallelic pathogenic mutations of the BRCA1 gene, with no or very subtle FA-features. She was diagnosed with ovarian cancer and breast cancer at the ages of 43 and 44 and had a strong family history of breast and gynecological cancers.  相似文献   
24.
为了充分挖掘多能源之间的互补潜力,使工业园区混合能源系统的配置方式由传统粗放式转变为精确优化配置并降低系统配置方案的保守性,基于粒子群联合CPLEX求解算法对工业园区的系统配置和运行调度方案进行分析优化,并以某生物园区为例进行了实例分析,得到了目标函数下的最优设计方案和运行策略。仿真分析结果表明,优化配置方法的应用能够协调冷热电多种能源的混合利用,提升系统的综合经济性。同时,为工业园区能源供应项目的规划、设计提供参考性支撑,丰富设计手段。  相似文献   
25.
26.
27.
Vacuum casting is one of the widely used methods for small-volume production of plastic parts. The main challenge of this method is to choose the optimal w  相似文献   
28.
针对古城煤矿S1303综采工作面切眼的地质构造与施工条件,提出了大断面切眼采用“锚网索+π型梁棚+预注浆”联合支护方案,有效地控制了大断面切眼留顶煤施工期间的支护难题,保障了S1303综采面切眼能够满足设计要求和如期完成施工,为同类条件下的切眼施工提供了一定参考。  相似文献   
29.
ABSTRACT

In this study, effect of calcium and gypsum on scheelite and fluorite was investigated using sodium oleate as collector. Micro-flotation and contact angle results showed that the adsorption of calcium could inhibit the hydrophobicity of scheelite and fluorite. Moreover, sulfate could enhance the inhibition. FT-IR results showed that calcium could be priori precipitated into calcium oleate and adsorb on mineral surface. The adsorption of calcium could increase the scheelite potential to IEP, while it showed limited effect on fluorite potential. However, the interaction of calcium on scheelite and fluorite in gypsum solution was more complex than that in calcium solution.  相似文献   
30.
Multimedia Systems - The preferences of Web information purchasers are changing. Cost-effectiveness (i.e., an emphasis on performance with respect to price) is becoming less regarded than...  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