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   4301篇
  免费   536篇
  国内免费   49篇
电工技术   87篇
综合类   82篇
化学工业   1049篇
金属工艺   201篇
机械仪表   286篇
建筑科学   75篇
矿业工程   8篇
能源动力   261篇
轻工业   370篇
水利工程   9篇
石油天然气   45篇
武器工业   2篇
无线电   730篇
一般工业技术   1007篇
冶金工业   225篇
原子能技术   46篇
自动化技术   403篇
  2024年   2篇
  2023年   41篇
  2022年   72篇
  2021年   128篇
  2020年   113篇
  2019年   157篇
  2018年   155篇
  2017年   177篇
  2016年   181篇
  2015年   201篇
  2014年   238篇
  2013年   329篇
  2012年   287篇
  2011年   350篇
  2010年   253篇
  2009年   232篇
  2008年   258篇
  2007年   171篇
  2006年   198篇
  2005年   134篇
  2004年   132篇
  2003年   167篇
  2002年   146篇
  2001年   134篇
  2000年   96篇
  1999年   92篇
  1998年   101篇
  1997年   60篇
  1996年   52篇
  1995年   38篇
  1994年   26篇
  1993年   33篇
  1992年   21篇
  1991年   18篇
  1990年   11篇
  1989年   12篇
  1988年   7篇
  1987年   8篇
  1986年   9篇
  1985年   7篇
  1984年   5篇
  1983年   6篇
  1981年   5篇
  1980年   5篇
  1979年   2篇
  1977年   4篇
  1976年   4篇
  1974年   2篇
  1968年   1篇
  1967年   1篇
排序方式: 共有4886条查询结果,搜索用时 15 毫秒
1.
Food Science and Biotechnology - Various hilling materials (rice hulls, pine sawdust, and perlite) were compared to produce sprout vegetables using beach silvertop (Glehnia littoralis Fr. Schm. ex...  相似文献   
2.
3.
4.
5.
6.
We demonstrate the structural evolution of polymorphic phases in Al2O3-inserted SrMnO3 ceramics synthesized by solid state reaction. While the 4H-hexagonal phase is predominant in pure SrMnO3 ceramics, a small amount of 6H-hexagonal polymorph is identified in addition to the primary 4H-hexagonal SrMnO3 and the secondary hexagonal SrAl2O4 phases in the as-sintered ceramics, evidenced by x-ray diffraction and subsequent Rietveld refinement analyses. The existence of the 6H-hexagonal SrMnO3 phase is corroborated using Raman spectroscopy. The chemical compositions and electronic structures of the Al2O3-inserted SrMnO3 compounds are also examined using energy dispersive spectroscopy and x-ray photoelectron spectroscopy, respectively. The first-principles calculations reveal that there is no clear difference between the total energies of 4H- and 6H-hexagonal polymorphs regardless of the presence/absence of Sr and oxygen vacancies. Possible origins are discussed with the estimation of actual strain based on the refined lattice parameter of 6H SrMnO3.  相似文献   
7.
8.
9.
The electrochemical reduction of carbon dioxide (CO2) to hydrocarbons is a challenging task because of the issues in controlling the efficiency and selectivity of the products. Among the various transition metals, copper has attracted attention as it yields more reduced and C2 products even while using mononuclear copper center as catalysts. In addition, it is found that reversible formation of copper nanoparticle acts as the real catalytically active site for the conversion of CO2 to reduced products. Here, it is demonstrated that the dinuclear molecular copper complex immobilized over graphitized mesoporous carbon can act as catalysts for the conversion of CO2 to hydrocarbons (methane and ethylene) up to 60%. Interestingly, high selectivity toward C2 product (40% faradaic efficiency) is achieved by a molecular complex based hybrid material from CO2 in 0.1 m KCl. In addition, the role of local pH, porous structure, and carbon support in limiting the mass transport to achieve the highly reduced products is demonstrated. Although the spectroscopic analysis of the catalysts exhibits molecular nature of the complex after 2 h bulk electrolysis, morphological study reveals that the newly generated copper cluster is the real active site during the catalytic reactions.  相似文献   
10.
Background: Epilepsy is a chronic neurological disorder characterized by the recurrence of seizures. One-third of patients with epilepsy may not respond to antiseizure drugs. Purpose: We aimed to examine whether D-limonene, a cyclic monoterpene, exhibited any antiseizure activity in the pentylenetetrazole (PTZ)-induced kindling mouse model and in vitro. Methods: PTZ kindling mouse model was established by administering PTZ (30 mg/kg) intraperitoneally to mice once every 48 h. We performed immunoblot blots, immunohistochemistry (IHC), and high-performance liquid chromatography (HPLC) analysis after the behavioral study. Results: An acute injection of PTZ (60 mg/kg) induced seizure in mice, while pretreatment with D-limonene inhibited PTZ-induced seizure. Repeated administration of PTZ (30 mg/kg) increased the seizure score gradually in mice, which was reduced in D-limonene (10 mg/kg)-pretreated group. In addition, D-limonene treatment increased glutamate decarboxylase-67 (GAD-67) expression in the hippocampus. Axonal sprouting of hippocampal neurons after kindling was inhibited by D-limonene pretreatment. Moreover, D-limonene reduced the expression levels of Neuronal PAS Domain Protein 4 (Npas4)-induced by PTZ. Furthermore, the adenosine A2A antagonist SCH58261 and ZM241385 inhibited anticonvulsant activity and gamma-aminobutyric acid (GABA)ergic neurotransmission-induced by D-limonene. Conclusion: These results suggest that D-limonene exhibits anticonvulsant activity through modulation of adenosine A2A receptors on GABAergic neuronal function.  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