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   51959篇
  免费   3215篇
  国内免费   1568篇
电工技术   1472篇
技术理论   4篇
综合类   2863篇
化学工业   14869篇
金属工艺   6703篇
机械仪表   1403篇
建筑科学   6446篇
矿业工程   1597篇
能源动力   996篇
轻工业   4805篇
水利工程   1792篇
石油天然气   1674篇
武器工业   146篇
无线电   1289篇
一般工业技术   4193篇
冶金工业   5023篇
原子能技术   399篇
自动化技术   1068篇
  2024年   196篇
  2023年   682篇
  2022年   2353篇
  2021年   2484篇
  2020年   1617篇
  2019年   1187篇
  2018年   1086篇
  2017年   1331篇
  2016年   1429篇
  2015年   1541篇
  2014年   2745篇
  2013年   2726篇
  2012年   3376篇
  2011年   3605篇
  2010年   3028篇
  2009年   3117篇
  2008年   2380篇
  2007年   3237篇
  2006年   3160篇
  2005年   2683篇
  2004年   2294篇
  2003年   2107篇
  2002年   1745篇
  2001年   1364篇
  2000年   1067篇
  1999年   816篇
  1998年   642篇
  1997年   514篇
  1996年   400篇
  1995年   380篇
  1994年   269篇
  1993年   200篇
  1992年   188篇
  1991年   150篇
  1990年   93篇
  1989年   121篇
  1988年   69篇
  1987年   67篇
  1986年   48篇
  1985年   46篇
  1984年   44篇
  1983年   36篇
  1982年   18篇
  1981年   5篇
  1980年   6篇
  1979年   5篇
  1966年   9篇
  1965年   7篇
  1964年   9篇
  1959年   7篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
金属PTC陶瓷复合材料结构及其导电机理   总被引:2,自引:0,他引:2  
杨海  余鸿飞 《压电与声光》1997,19(3):196-200
研究了金属PTC陶瓷复合材料的电学性能和其材料组分。结果表明,掺入金属的PTC陶瓷材料经氮气中烧结,然后在空气中进行热处理,材料表面形成高势垒层,金属PTC陶瓷复合材料的室温电阻较PTC的陶瓷高。样品之中存在大量不同类型的极化,在低温时样品电阻较高,温度增加后,大量各种类型离子极化出现,在变价金属铁的变价导电作用下,削弱表面势垒,使金属PTC陶瓷复合材料电阻降低,表现出NTC现象。在电场作用下,正负电荷、晶粒畸变和空位缺陷等产生空间电荷极化使金属PTC陶瓷复合材料有较高介电常数。介电损耗(tgδ)频谱和介电δ温度谱上都出现一个介电峰,其主要原因是跃迁极化,金属阳离子由一个位置跃迁到另一个位置,在介电损耗所对应的频率和温度时出现跃迁极化率最大  相似文献   
72.
本文从理论和实践上综述了磁化水的特性、磁化机理、国内外的发展近况及其使用安装等。该法用于锅炉和各类冷却水处理有广泛的前景。  相似文献   
73.
A mathematical model was developed to simulate water movement, mass transport, and nitrogen transformations in soils during wastewater applications. The model is one-dimensional and based on the Galerkin finite-element method. The submodel of mass transport of nitrogen incorporates the convection-dispersion processes of ammonium and nitrate nitrogen, nitrification, denitrification, ammonium exchange and uptake of ammonium and nitrate ions. The accuracy and validity of the proposed model was examined by comparison with an explicit-implicit finite-difference model results. The model was used for simulation of water and nitrogen dynamics during wastewater application in homogeneous and multi-layered soils under different N concentration, rate, duration and scheduling of application.  相似文献   
74.
Reviews the book, The chemically dependent: Phases of treatment and recovery edited by Barbara C. Wallace (see record 1992-98403-000). While this book is ambitious, interesting, educational, and useful, it is also disappointing, repetitious, and incomplete. Because it tries to accomplish so much, it may appear to have succeeded too little. This book is organized around, and explicative of, several basic ideas which might have been controversial if not heretical had this book been published ten years ago. Section I, purporting to link specific "phases of recovery" to particular forms and functions of treatment, will certainly be useful for novice clinicians but falls short of its overstated goals and is thereby disappointing. Section II is a collection of moderately redundant chapters describing the etiology and treatment of substance abusers from the viewpoints of psychoanalytic, psychodynamic, ego psychology, and object-relations theorists and therapists. Section III focuses on cognitive-behavioral, self-help, and relapse-prevention treatments. Section IV is quite uneven in quality of writing and applicability of content, and could have benefited from closer editorial scrutiny or selectivity. The final section focuses on special needs of particular subpopulations of substance abusers: African-Americans, prison inmates, HIV/AIDS patients, persons who are homeless, those who have been sexually and physically abused, and others. According to the reviewer this is not the best book on substance abuse treatment, but it does present some clinically useful ideas and it is worth reading. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
75.
通过对典型振冲挤密法施工方法的研究,分析了该方法的加固机理,指出它可提高地基承载力、减少沉降和不均匀沉降,且能达到地基抗地震、抗液化能力的效果。  相似文献   
76.
Laboratory-scale and parametric experiments of SO2 and NOx removal from the simulated combustion gas by pulsed corona discharge have been performed by changing the combustion gas composition and temperature, the electrode configuration of plasma reactor, and the polarity of high-voltage electrode. The following results are obtained: 1) the higher the concentration of H2O and O2, the higher the efficiency of desulfurization and denitrification at the same specific input; 2) the pulsed corona discharge with a voltage pulsewidth as short as 200 ns of negative polarity shows the possibility to attain almost 90 percent deSOx and deNOx efficiency at the specific discharge input of 20 J/g, which is almost the same as the specific input in the electron-beam process; 3) the deNOx characteristics show a little temperature dependence in the range of 70 to 130°C, but the deSOx efficiency increases rapidly in the temperature region below 100°C suggesting the thermochemical dependence of deSOx reaction; 4) when desulfurization and denitrification proceed, the white dendritic powder deposits on the plasma reactor whose composition is identified to be 49 mol% (NH4)2SO4 and 47 mol% of 2NH4NO3 · (NH4)2SO4, and the ratio of SO2, NO and NH3 of the deposit is almost equal to that of supplied gas.  相似文献   
77.
激光远距作用的机制与效应   总被引:1,自引:0,他引:1  
本文定量分析激光远距作用的机理并对它们在治癌中的作用作简要的论述。  相似文献   
78.
Wide variability exists with respect to how breast cancer survivors respond to common psychological and psychosocial challenges of their disease, ranging from posttraumatic stress disorder to posttraumatic growth. This cross-sectional study examined contextual, disease-related, and intraindividual predictors of posttraumatic growth in 224 randomly selected breast cancer survivors. A series of hierarchical regression analyses found that age at diagnosis, marital status, employment, education, perceived intensity of disease, and active coping accounted for 34%, 35%, and 28% of the variance in growth in relationships with others, new possibilities, and appreciation for life. These findings suggest that a more comprehensive model of growth will be helpful in understanding the various factors that play a role in breast cancer survivors' perception of psychological and psychosocial growth. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
79.
吴硕 《山西建筑》2006,32(20):13-14
通过对广州市猎德污水处理厂的介绍,说明本工程厂区平面根据规划用地、工艺流程、外部及内部环境因地制宜进行布置,建筑立面造型综合考虑厂房的不同使用功能,力求打破以往的工业建筑模式,建成处处以人为本的生态花园式厂房。  相似文献   
80.
三峡永久船闸结构缝渗漏处理技术   总被引:1,自引:0,他引:1  
林金良 《水力发电》2003,29(8):32-34
在三峡永久船闸结构缝处理过程中,认真分析了结构缝渗漏的原因,通过止水检查槽进行压水检查,确定了渗漏部位。结合渗漏具体情况,采取了结构缝表面嵌填止水材料和廊道周边止水检查槽灌浆相结合的处理方法。在实施过程中,采用了多种新材料和新工艺,取得了良好的效果。  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