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   16993篇
  免费   212篇
  国内免费   25篇
电工技术   189篇
综合类   4篇
化学工业   2009篇
金属工艺   363篇
机械仪表   338篇
建筑科学   512篇
矿业工程   60篇
能源动力   306篇
轻工业   1214篇
水利工程   89篇
石油天然气   118篇
无线电   1509篇
一般工业技术   2335篇
冶金工业   6627篇
原子能技术   159篇
自动化技术   1398篇
  2022年   79篇
  2021年   101篇
  2019年   102篇
  2018年   135篇
  2017年   101篇
  2016年   94篇
  2015年   108篇
  2014年   226篇
  2013年   569篇
  2012年   304篇
  2011年   407篇
  2010年   332篇
  2009年   337篇
  2008年   450篇
  2007年   439篇
  2006年   432篇
  2005年   386篇
  2004年   323篇
  2003年   360篇
  2002年   309篇
  2001年   322篇
  2000年   316篇
  1999年   467篇
  1998年   1879篇
  1997年   1162篇
  1996年   799篇
  1995年   551篇
  1994年   486篇
  1993年   523篇
  1992年   285篇
  1991年   259篇
  1990年   273篇
  1989年   234篇
  1988年   251篇
  1987年   222篇
  1986年   209篇
  1985年   273篇
  1984年   208篇
  1983年   208篇
  1982年   207篇
  1981年   189篇
  1980年   207篇
  1979年   130篇
  1978年   140篇
  1977年   285篇
  1976年   437篇
  1975年   137篇
  1974年   125篇
  1973年   107篇
  1970年   83篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Clonality in T-cell malignancy was investigated using T-cell receptor (TcR) V beta 1-20 family primers and polymerase chain reaction amplification (PCR) of cDNA prepared from tissue biopsies and blood involved with tumour. Secondary PCR amplification of the VDJ joints of primary PCR products was performed to distinguish clonal from polyclonal products, and clonal V beta gene products were confirmed by direct PCR sequencing in the majority of cases. In eight T-cell malignancies including T-cell acute lymphoblastic leukaemia (T-ALL) and T-cell chronic lymphocytic leukaemia (T-CLL) shown to be clonal by Southern blot analysis, one or two primary PCR products were identified and shown to be clonal. In five cases of peripheral T-cell lymphoma (PTCL) all V beta 1-20 families were identified after primary PCR amplification, and clonal products were identified in two cases after secondary amplification; TcR V beta clonal families could not be demonstrated in the remaining three cases. These data were in agreement with previous Southern blot analysis of these cases, and confirmed the presence of reactive T cells in PTCL as well as providing further evidence for the genotypic heterogeneity of this entity. In the remaining case, a blood lymphocytosis, primary PCR amplification produced predominant TcR V beta 6 and V beta 12 family products, of which the V beta 6 family proved clonal after secondary PCR amplification. There was no evidence for overrepresentation of TCR V beta families by the tumour populations in this study, furthermore the data confirm the involvement of reactive cells in T-cell malignancy and the genetic heterogeneity of PTCL.  相似文献   
92.
93.
Various definitions exist for what constitutes family therapy. In this article, we consider family therapy to encompass any intervention that targets family interactions and conceptualizes problems as existing beyond individual clients. Numerous individual studies and several quantitative reviews have established family therapy as an effective treatment modality and the treatment of choice for many disorders. However, critiques of existing service provision highlight the unfortunate fact that numerous barriers to treatment exist at multiple levels of the broader ecology, preventing many families from benefiting from these services. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
94.
Multisystemic therapy (MST) delivered through a community mental health center was compared with usual services delivered by a Department of Youth Services in the treatment of 84 serious juvenile offenders and their multiproblem families. Offenders were assigned randomly to treatment conditions. Pretreatment and posttreatment assessment batteries evaluating family relations, peer relations, symptomatology, social competence, and self-reported delinquency were completed by the youth and a parent, and archival records were searched at 59 wks postreferral to obtain data on rearrest and incarceration. In comparison with youths who received usual services, youths who received MST had fewer arrests and self-reported offenses and spent an average of 10 fewer weeks incarcerated. In addition, families in the MST condition reported increased family cohesion and decreased youth aggression in peer relations. The relative effectiveness of MST was neither moderated by demographic characteristics nor mediated by psychosocial variables. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
95.
96.
The ability of rotorcraft to fly at low altitude is hindered by the high pilot workload required to avoid obstacles. The development of automation tools that can detect obstacles in the rotorcraft flight path, warn the crew, and interact with the guidance system to avoid detected obstacles would significantly reduce pilot workload and increase safety. This article describes an obstacle detection approach based on feature tracking and recursive range estimation that takes into account the characteristics of rotorcraft flight. The merits and weaknesses of the approach are discussed using image sequences from the laboratory and from flight. © 1992 John Wiley & Sons, Inc.  相似文献   
97.
This article quantifies errors arising from various integration methods and from sampling density in the numerical estimation of colorimetric integrals, e.g., tristimulus values. Both data sampling density and various numerical integration method errors will be distinguished. A test is presented to quantify sampling interval requirements for accurate colorimetric calculations for various illuminants. © 1992 John Wiley & Sons, Inc.  相似文献   
98.
99.
Criticizes J. G. Blight's (see record 1987-16803-001) use of references, his identification with the policy of deterrence, his dismissal of approaches to reversing the nuclear arms race, and his discussion of a sociobiology of war. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
100.
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