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   117680篇
  免费   12280篇
  国内免费   7497篇
电工技术   9281篇
技术理论   3篇
综合类   11637篇
化学工业   15375篇
金属工艺   5308篇
机械仪表   9994篇
建筑科学   11623篇
矿业工程   9753篇
能源动力   7127篇
轻工业   3643篇
水利工程   9350篇
石油天然气   9004篇
武器工业   1330篇
无线电   4289篇
一般工业技术   7519篇
冶金工业   6806篇
原子能技术   1948篇
自动化技术   13467篇
  2024年   502篇
  2023年   1486篇
  2022年   2973篇
  2021年   3623篇
  2020年   3845篇
  2019年   3137篇
  2018年   2943篇
  2017年   3605篇
  2016年   4256篇
  2015年   4550篇
  2014年   7264篇
  2013年   7256篇
  2012年   8971篇
  2011年   9484篇
  2010年   6945篇
  2009年   7151篇
  2008年   6581篇
  2007年   8016篇
  2006年   7280篇
  2005年   6345篇
  2004年   5247篇
  2003年   4632篇
  2002年   3855篇
  2001年   3142篇
  2000年   2603篇
  1999年   2131篇
  1998年   1683篇
  1997年   1464篇
  1996年   1323篇
  1995年   1136篇
  1994年   946篇
  1993年   659篇
  1992年   552篇
  1991年   376篇
  1990年   338篇
  1989年   277篇
  1988年   184篇
  1987年   163篇
  1986年   98篇
  1985年   65篇
  1984年   91篇
  1983年   62篇
  1982年   34篇
  1981年   18篇
  1980年   22篇
  1979年   30篇
  1977年   8篇
  1974年   7篇
  1959年   26篇
  1951年   32篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
This paper presents an inelastic element for the analysis of beams on foundations. The element is derived from a two-field mixed formulation with independent approximation of forces and displacements. The state determination algorithm for the implementation of the element in a general purpose nonlinear finite element analysis program is presented and its stability characteristics are discussed. Numerical studies are performed to compare the model with the classical displacement formulation. The studies confirm the superiority of the proposed model in describing the inelastic behavior of beams on foundations.  相似文献   
103.
This study examined organizational family-responsive policies, perceptions of the organization as family supportive, and supervisor support as issues that may be salient to the experience of conflict between paid employment (work) and family roles. Data were collected from 355 managerial personnel in New Zealand. Although work-family conflict and psychological strain were strongly linked, the availability of organizational policies had no significant association with levels of conflict or strain, whereas policy usage was related only to work-to-family interference and not to family-to-work interference. On the other hand, perceptions of the organization as family supportive and supervisor support for work-family balance displayed significant relationships with key variables, highlighting the importance of these variables for interventions designed to ameliorate the negative impact of work-family conflict on managerial well-being. Implications for the effective implementation of family-responsive interventions are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
104.
Using self-determination theory, the authors tested a motivational model to explain the conditions under which rural students formulate their intentions to persist in, versus drop out of, high school. The model argues that motivational variables underlie students' intentions to drop out and that students' motivation can be either supported in the classroom by autonomy-supportive teachers or frustrated by controlling teachers. LISREL analyses of questionnaire data from 483 rural high school students showed that the provision of autonomy support within classrooms predicted students' self-determined motivation and perceived competence. These motivational resources, in turn, predicted students' intentions to persist, versus drop out, and they did so even after controlling for the effect of achievement. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
105.
对企业账面利润与现金流量关系的认识   总被引:3,自引:0,他引:3  
吴琳娜  王熠 《铜业工程》2004,(3):77-78,48
本文阐述了企业账面利润与现金流量的关系 ,指出了企业账面利润与现金流量的四个不同点 ,并且提出了一个现代企业应如何在四个方面做好工作 ,正确处理好这两者的关系。  相似文献   
106.
Risk factors affecting the course of posttraumatic stress disorder (PTSD) are poorly understood. As part of a larger study on characterizing exposure to herbicides in Vietnam, the authors investigated this issue in a random sample of 1,377 American Legionnaires who had served in Southeast Asia during the Vietnam War and were followed over a 14-year period. High combat exposure, perceived negative community attitudes at homecoming, minority race, depression symptoms at Time 1, and more anger at Time 1 predicted a more chronic course. Community involvement at Time 1 was protective and associated with decreased risk at Time 2. Discomfort in disclosing Vietnam experiences was associated with an increased risk for developing PTSD but did not predict its course. Combat exposure predicted PTSD course more strongly than any other risk factor. Findings suggest recovery from PTSD is significantly influenced by perceived social support. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
107.
近十年来,天铁集团炼铁厂通过改善原燃料条件;优化炉料结构,提高入炉品位;采用提高炉顶压力、富氧喷煤、低硅冶炼、炉顶气象系统等多项先进技术,使高炉各项经济技术指标逐年提高。  相似文献   
108.
ListofSymbol  B———Buoyancy ,m·s- 2 ;  c———Concentrationofsoluteelement ;  Cμ———Turbulentconstant;  D———Diffusivityofsoluteelement ,m2 ·s- 1 ;  fl,fs———Liquidandsolidfraction ;  fμ———Turbulentcoefficient ;  h———Enthalpy ,J·kg- 1 ;  k———Turbulentkineticenergy ,m2 ·s- 2 ;  kp———Equilibriumpartitioncoefficient;  Kp———Permeabilityofmushyzone ,m2 ;  K0 ———Permeabilitycoefficient;  p———Pressure ,Pa ;  Pr———Prandtlnumber ;…  相似文献   
109.
变压器有载合闸过程中故障分闸后铁心剩磁分析   总被引:3,自引:0,他引:3  
通过有载合闸变压器模型,分析了变压器有载合闸过程中由于副边突然短路导致主保护动作时电流和磁通的暂态过程,并对变压器铁心内的剩磁作了定性的分析。  相似文献   
110.
A finite element scheme is presented to model the dissociation of gas hydrates in porous media by hot water injection. We show a complete derivation of the finite element formulation, including the associated mass and energy conservation equations capable of performing transient analysis of both conductive and convective heat transfer for gas and liquid flow in porous media. The scheme also includes the latent heat effect to accommodate the change of phase due to melting of hydrate. In the companion paper, Part II, this method is successfully applied to hydrate reservoirs.  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