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   73819篇
  免费   7264篇
  国内免费   4532篇
电工技术   5454篇
技术理论   4篇
综合类   6001篇
化学工业   10969篇
金属工艺   4486篇
机械仪表   4581篇
建筑科学   5714篇
矿业工程   2234篇
能源动力   1933篇
轻工业   8073篇
水利工程   1761篇
石油天然气   3462篇
武器工业   835篇
无线电   8102篇
一般工业技术   7464篇
冶金工业   3316篇
原子能技术   787篇
自动化技术   10439篇
  2024年   311篇
  2023年   1157篇
  2022年   2398篇
  2021年   3200篇
  2020年   2445篇
  2019年   1915篇
  2018年   2180篇
  2017年   2377篇
  2016年   2196篇
  2015年   3300篇
  2014年   4007篇
  2013年   4894篇
  2012年   5748篇
  2011年   6177篇
  2010年   5590篇
  2009年   5296篇
  2008年   5342篇
  2007年   4964篇
  2006年   4399篇
  2005年   3572篇
  2004年   2558篇
  2003年   2140篇
  2002年   2017篇
  2001年   1702篇
  2000年   1245篇
  1999年   995篇
  1998年   665篇
  1997年   562篇
  1996年   460篇
  1995年   396篇
  1994年   301篇
  1993年   217篇
  1992年   163篇
  1991年   151篇
  1990年   122篇
  1989年   81篇
  1988年   52篇
  1987年   36篇
  1986年   45篇
  1985年   32篇
  1984年   25篇
  1983年   18篇
  1982年   22篇
  1981年   13篇
  1980年   34篇
  1979年   13篇
  1977年   13篇
  1976年   11篇
  1973年   7篇
  1959年   9篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
随着市场的发展,精品超市和改造店铺逐渐增多,需要一种更加适合的制冷机组来满足市场的需求。本文提供了一种新型的解决方案,解决了现有机组存在的高噪音和高成本问题,不仅提高了制冷效率,而且节约能源,保护环境。  相似文献   
32.
33.
34.
35.
在国家政策和市场需求的双重推动下,BIM技术在国内建筑领域迎来快速发展阶段,从最初的概念普及,到能够局部应用,再到现在能够全过程应用,其趋势是十分明确的,但是在其发展的过程中仍然存在着不少问题,如传统技术与BIM技术深入融合问题,BIM技术如何解决工程施工现场实际问题等.本文主要研究BIM技术在连云港民用机场迁建工程旅客过夜用房酒店项目中的综合应用,从协同建模、碰撞检查、管线综合、施工图深化出图及漫游展示等方面着手,着重解决BIM技术在施工过程中应用的落地问题,从而达到提高效率,缩短工期,降低成本,提升质量的目标.  相似文献   
36.
37.
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   
38.
Through the simple precipitation of palygorskite (PGS) by zinc borate (ZB) (to make PGS@ZB) and the decoration of PGS@ZB by dodecylamine (N), a novel organic‐inorganic@inorganic hybrid flame retardant of PGS@ZB‐N was prepared and was incorporated with ethylene vinyl acetate copolymer (EVA) to improve its flame retardance. The structure and morphology of PGS@ZB‐N were characterized by Fourier transform infrared (FTIR) spectroscopy, X‐ray diffraction (XRD), and scanning electron microscopy (SEM), and it was confirmed that the PGS@ZB‐N hybrid had been successfully prepared. The flame retardancy and burning behavior of EVA/PGS@ZB‐N/EG (EG = expandable graphite) composite were studied through thermogravimetric analysis (TGA), limiting oxygen index (LOI), UL‐94 (by the vertical burning test), and cone calorimeter test (CCT) characterizations. The prepared EVA/PGS@ZB‐N/EG composite obtained an LOI value of 41.2% with the addition of 30 wt% PGS@ZB‐N/EG. It was found that EVA/PGS@ZB‐N/EG was protected through a gas phase and condensed phase alternating synergistic effect mechanism.  相似文献   
39.
40.
The potential use of stem cell-based therapies for the repair and regeneration of various tissues and organs is a major goal in repair medicine. Stem cells are classified by their potential to differentiate into functional cells. Compared with other sources, adipose-derived stem cells (ADSCs) have the advantage of being abundant and easy to obtain. ADSCs are considered to be tools for replacing, repairing, and regenerating dead or damaged cells. The capacity of ADSCs to maintain their properties depends on the balance of complex signals in their microenvironment. Their properties and the associated outcomes are in part regulated by reactive oxygen species, which mediate the oxidation-reduction state of cells as a secondary messenger. ADSC therapy has demonstrated beneficial effects, suggesting that secreted factors may provide protection. There is evidence that ADSCs secrete a number of cytokines, growth factors, and antioxidant factors into their microenvironment, thus regulating intracellular signaling pathways in neighboring cells. In this review, we introduce the roles of ADSCs in the protection of cells by modulating inflammation and immunity, and we develop their potential therapeutic properties.  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