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   343052篇
  免费   12868篇
  国内免费   6491篇
电工技术   11447篇
技术理论   6篇
综合类   7559篇
化学工业   54536篇
金属工艺   16199篇
机械仪表   13572篇
建筑科学   13452篇
矿业工程   4523篇
能源动力   7789篇
轻工业   31143篇
水利工程   4670篇
石油天然气   10283篇
武器工业   1111篇
无线电   37689篇
一般工业技术   58080篇
冶金工业   50563篇
原子能技术   6593篇
自动化技术   33196篇
  2022年   3734篇
  2021年   5863篇
  2020年   4191篇
  2019年   4143篇
  2018年   5640篇
  2017年   5916篇
  2016年   6057篇
  2015年   6462篇
  2014年   8980篇
  2013年   16611篇
  2012年   13720篇
  2011年   16640篇
  2010年   14080篇
  2009年   14601篇
  2008年   15125篇
  2007年   15083篇
  2006年   13456篇
  2005年   11704篇
  2004年   9543篇
  2003年   8619篇
  2002年   8459篇
  2001年   8291篇
  2000年   7580篇
  1999年   7470篇
  1998年   13908篇
  1997年   10480篇
  1996年   8104篇
  1995年   6206篇
  1994年   5632篇
  1993年   5353篇
  1992年   4256篇
  1991年   3989篇
  1990年   4024篇
  1989年   3933篇
  1988年   3662篇
  1987年   3098篇
  1986年   3118篇
  1985年   3437篇
  1984年   3349篇
  1983年   3085篇
  1982年   2720篇
  1981年   2915篇
  1980年   2661篇
  1979年   2847篇
  1978年   2743篇
  1977年   2846篇
  1976年   3700篇
  1975年   2460篇
  1974年   2293篇
  1973年   2322篇
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
121.
Water Resources Management - Public awareness of water quality concerns has increased since the Flint, MI crisis, but knowledge about water resources management remains low. Consequently,...  相似文献   
122.
Microsystem Technologies - The strategy for analysis of noise generated in the analog circuit is presented here. Further, methodology for optimization of noise to improve the performance of the...  相似文献   
123.
Sarcopenia is the loss of skeletal muscle mass and function with advancing age. It involves both complex genetic and modifiable risk factors, such as lack of exercise, malnutrition and reduced neurological drive. Cognitive decline refers to diminished or impaired mental and/or intellectual functioning. Contracting skeletal muscle is a major source of neurotrophic factors, including brain-derived neurotrophic factor, which regulate synapses in the brain. Furthermore, skeletal muscle activity has important immune and redox effects that modify brain function and reduce muscle catabolism. The identification of common risk factors and underlying mechanisms for sarcopenia and cognition may allow the development of targeted interventions that slow or reverse sarcopenia and also certain forms of cognitive decline. However, the links between cognition and skeletal muscle have not been elucidated fully. This review provides a critical appraisal of the literature on the relationship between skeletal muscle health and cognition. The literature suggests that sarcopenia and cognitive decline share pathophysiological pathways. Ageing plays a role in both skeletal muscle deterioration and cognitive decline. Furthermore, lifestyle risk factors, such as physical inactivity, poor diet and smoking, are common to both disorders, so their potential role in the muscle–brain relationship warrants investigation.  相似文献   
124.
A series of 2-phenyloxazoles bearing an amide group at position 4 were designed and synthesized for evaluation as potential inhibitors of human recombinant monoamine oxidases (hrMAOs). Results of kinetics experiments demonstrated that all compounds behave as competitive MAO inhibitors, with good selectivity toward the MAO-B isoform. The most potent and selective derivatives are characterized by inhibition constant (Ki) values in the sub-micromolar range and a good selectivity index (Ki MAO-A/Ki MAO-B>50). Some derivatives were also found to be able to inhibit MAO activity in nerve growth factor (NGF)-differentiated PC12 cells, taken as a model of neuronal cells. In particular, 2-(2-hydroxyphenyl)-N-phenyloxazole-4-carboxamide (compound 4 a ) may be a promising new scaffold, exerting the highest selectivity and inhibitory effect toward MAOs in NGF-differentiated PC12 cell lysates, without compromising cell viability. Molecular docking analysis allowed a rationalization of the experimentally observed binding affinity and selectivity.  相似文献   
125.
Ji  Chengang  Yang  Chenying  Shen  Weidong  Lee  Kyu-Tae  Zhang  Yueguang  Liu  Xu  Guo  L. Jay 《Nano Research》2019,12(3):543-548

We present a new scheme for visibly-opaque but near-infrared-transmitting filters involving 7 layers based on one-dimensional ternary photonic crystals, with capabilities in reaching nearly 100% transmission efficiency in the near-infrared region. Different decorative reflection colors can be created by adding additional three layers while maintaining the near-infrared transmission performance. In addition, our proposed structural colors show great angular insensitivity up to ±60° for both transverse electric and transverse magnetic polarizations, which are highly desired in various fields. The facile strategy described here involves a simple deposition method for the fabrication, thereby having great potential in diverse applications such as image sensors, anti-counterfeit tag, and optical measurement systems.

  相似文献   
126.
127.
128.
129.
130.
A technology for slag formation in the ladle–furnace unit is considered; the slag is based on the CaO–SiO2–MgO–Al2O3–B2O3 system. This technology permits both microalloying of the steel with boron (reduced from the oxide phase) and desulfurization of the steel. The resulting boron content in the steel is 0.001–0.008%; the sulfur content in low-alloy steel and pipe steel is low (0.004–0.010%); and the consumption of manganese ferroalloys is reduced to 0.5 kg/t for 08кп steel and 1.4 kg/t for 09Г2C steel. In addition, the proposed technology increases the strength of the rolled steel, without loss in its plasticity; and reduces the environmental impact thanks to the replacement of fluorspar by colemanite.  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