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   151123篇
  免费   12466篇
  国内免费   7045篇
电工技术   17714篇
技术理论   31篇
综合类   13936篇
化学工业   11188篇
金属工艺   3761篇
机械仪表   7173篇
建筑科学   23615篇
矿业工程   5330篇
能源动力   14333篇
轻工业   3990篇
水利工程   5827篇
石油天然气   4824篇
武器工业   1151篇
无线电   12573篇
一般工业技术   11326篇
冶金工业   8475篇
原子能技术   1726篇
自动化技术   23661篇
  2024年   653篇
  2023年   2250篇
  2022年   3892篇
  2021年   4609篇
  2020年   4914篇
  2019年   3910篇
  2018年   3474篇
  2017年   4342篇
  2016年   5074篇
  2015年   5272篇
  2014年   11653篇
  2013年   9920篇
  2012年   11191篇
  2011年   12113篇
  2010年   9268篇
  2009年   9627篇
  2008年   9158篇
  2007年   10639篇
  2006年   8867篇
  2005年   7270篇
  2004年   6150篇
  2003年   5378篇
  2002年   4379篇
  2001年   3419篇
  2000年   2782篇
  1999年   2133篇
  1998年   1553篇
  1997年   1210篇
  1996年   1039篇
  1995年   828篇
  1994年   675篇
  1993年   512篇
  1992年   372篇
  1991年   322篇
  1990年   257篇
  1989年   241篇
  1988年   196篇
  1987年   129篇
  1986年   135篇
  1985年   167篇
  1984年   157篇
  1983年   129篇
  1982年   92篇
  1981年   51篇
  1980年   51篇
  1979年   39篇
  1978年   18篇
  1977年   25篇
  1959年   15篇
  1951年   13篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
141.
142.
In this study, a single unit of planar micro-solid-oxide fuel cell (μSOFC) is investigated numerically to evaluate the influences of flow channel design, oxygen composition, and thermal operating conditions on cell performance. Four flow channel designs are examined under the co-flow configuration: serpentine, double serpentine, rod bundle, and oblique rib. For all designs, the contacts areas of interconnect to electrodes are kept consistent to maintain the ohmic losses at the same level. To characterize the mass transport effects, there are three different compositions, 100% O2, 50% O2/50% N2 and air, fed to the cathode inlet. Different thermal conditions, adiabatic and isothermal, are applied to the outer boundary of the μSOFC and the results are compared. The outcomes suggest that both thermal conditions and oxidant composition show remarkable influences on μSOFC performance. Under adiabatic conditions, the rise of cell temperature causes a decrease in reversible voltage, deteriorating the overall cell competence. When oxygen is diluted with nitrogen, local gas diffusion becomes dominant to the cathode reaction. Bulk flow, on the other hand, plays a minor role in cell performance since there is little deviation in the polarization curves for all flow channel designs, even at high current densities. For comparison, the flow visualization technique is employed to observe the transport phenomena in various flow channel designs. The flow patterns are found to resemble the concentration distribution, providing a useful tool to design μSOFCs.  相似文献   
143.
绿色供应链管理的基本原理   总被引:39,自引:0,他引:39  
人口、资源与环境三者之间的矛盾日益突显,要求制造业提高其活动与环境的相容性。绿色供应链管理是从系统的观点与集成的思想出发解决制造业与环境之间冲突的有效方式。从可持续发展的思想出发建立了绿色供应链的概念模型,分析了绿色供应链管理的目标,在此基础上探讨了绿色供应链管理的基本原理,认为共生原理、循环原理、替代转换原理与系统开放原理是实施绿色供应链管理应该遵循的基本原理。  相似文献   
144.
罗坡坝水电站拱坝设置有三个溢流表孔,中间孔高程低于两侧的孔,三个泄水孔设有差动式挑坎。通过模型试验表明,不发生危及岸坡稳定的泄流雾化问题,此外,适当控制泄流水舌射程可以减少坝下冲坑深度,消能效果良好。  相似文献   
145.
Supply chain management has offered a way to improve the industrial environment becomes more competitive. While, the commonly seen methodologies may be effective in solving the production–distribution problem only from supplier- or customer-oriented consideration, those cannot present the interactive relationship between upstream and downstream enterprises. In the competitive semiconductor industry environment, considering the viewpoints of the supplier and consumer simultaneously is particularly required, because multiple manufacturing and demanding steps are performed at separate situations, concurrently. In this paper, we propose an interaction-oriented approach, which bases on the analytic hierarchy process (AHP) methodology and proportional rule, to solve the semiconductor distribution problem with multiple quantitative and qualitative criteria. The developed approach gives an expected satisfaction for the all participators of the whole chain while the cooperative information is shared perfectly and effectively. Analysis results demonstrate the proposed methodology is efficient and effective through a real world case study.  相似文献   
146.
Creep crack growth rates were measured using centrally cracked tension specimens of thin polypropylene film with different crack lengths at various stresses and temperatures. The creep crack growth rates were correlated with the stress intensity factor. There was the region of the minimum constant crack growth rate which occupied more than 70% of the total creep failure life. This constant creep crack growth rate characteristics were analyzed on the basis of the stress-dependent Arrhenius type thermally activated process.  相似文献   
147.
高职高专现代教育技术管理体制之我见   总被引:3,自引:1,他引:2  
本文从教育技术的含义和发展的历史出发,分析目前高职高专院校的教育技术管理体制现状,提出应建立完善的教育技术管理体制,以推进教育技术工作的协调发展。  相似文献   
148.
企业诚信经营浅议   总被引:3,自引:0,他引:3  
以大量史实分析了国内外企业经营的诚信问题,诚信经营在企业发展中的重要性以及如何健全企业诚信机制等相关问题,并呼吁各商家企业严格遵守企业诚信经营准则。  相似文献   
149.
论述了制定《航空工业材料及热工艺技术工作规定》的必要性和航空材料及热工艺的内涵及其重要性,提出确保航空产品质量是航空材料及热工艺技术管理工作的永恒主题,而加强和健全航空材料及热工艺技术管理机构,完善其规章制度则是保证航空产品质量的重要措施,该机构的主要职责是技术立法、技术发展和技术归口。  相似文献   
150.
Reviews the book, Depression in the medically ill: An integrated approach by G. Rodin, J. Craven, and C. Littlefield (see record 1991-97973-000). This book provides an in-depth coverage of current issues in the management of depression in the medically ill. The book is balanced in theoretical perspective and quite comprehensive in coverage of the empirical literature. The authors are well known to the area of depression and physical illness. The book is organized into three main sections dealing with 1) Clinical Presentation, 2) Etiology and Pathogenesis, and 3) Treatment. Numerous case examples are provided throughout to highlight different aspects of symptom presentation, diagnostic problems, and therapeutic management. Notably lacking from the review of prevalence studies is the work examining depression and chronic pain populations. In sum, Rodin et al. have drawn on a vast literature to provide a clear and coherent picture of the current state of knowledge and theory dealing with depression and medical illness. Their book joins a number of recent papers attempting to draw more attention to clinical issues in the management of depression in the medically ill. I would recommend the book to all clinicians who work with medically ill populations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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