全文获取类型
收费全文 | 15181篇 |
免费 | 219篇 |
国内免费 | 23篇 |
专业分类
电工技术 | 191篇 |
综合类 | 5篇 |
化学工业 | 2028篇 |
金属工艺 | 364篇 |
机械仪表 | 342篇 |
建筑科学 | 515篇 |
矿业工程 | 60篇 |
能源动力 | 312篇 |
轻工业 | 1215篇 |
水利工程 | 90篇 |
石油天然气 | 118篇 |
无线电 | 1536篇 |
一般工业技术 | 2354篇 |
冶金工业 | 4729篇 |
原子能技术 | 159篇 |
自动化技术 | 1405篇 |
出版年
2022年 | 79篇 |
2021年 | 107篇 |
2019年 | 105篇 |
2018年 | 140篇 |
2017年 | 104篇 |
2016年 | 95篇 |
2015年 | 111篇 |
2014年 | 228篇 |
2013年 | 577篇 |
2012年 | 311篇 |
2011年 | 413篇 |
2010年 | 339篇 |
2009年 | 342篇 |
2008年 | 453篇 |
2007年 | 440篇 |
2006年 | 435篇 |
2005年 | 388篇 |
2004年 | 326篇 |
2003年 | 361篇 |
2002年 | 311篇 |
2001年 | 321篇 |
2000年 | 316篇 |
1999年 | 386篇 |
1998年 | 1323篇 |
1997年 | 839篇 |
1996年 | 604篇 |
1995年 | 424篇 |
1994年 | 378篇 |
1993年 | 396篇 |
1992年 | 274篇 |
1991年 | 244篇 |
1990年 | 257篇 |
1989年 | 215篇 |
1988年 | 220篇 |
1987年 | 202篇 |
1986年 | 195篇 |
1985年 | 249篇 |
1984年 | 208篇 |
1983年 | 205篇 |
1982年 | 200篇 |
1981年 | 178篇 |
1980年 | 192篇 |
1979年 | 128篇 |
1978年 | 134篇 |
1977年 | 235篇 |
1976年 | 317篇 |
1975年 | 135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
71.
The treatment of patients with uterine neoplasms may be significantly altered by the stage of disease at the time of diagnosis. A noninvasive and accurate means of staging these tumors is therefore desirable. This article discusses the magnetic resonance imaging techniques and findings that are essential for the accurate staging of uterine neoplasms. The imaging findings are presented following a discussion of the histopathologic findings, clinical presentation, diagnosis and staging, pathways of tumor spread, and treatment of each neoplasm. A comparison of magnetic resonance and other imaging techniques is also provided. 相似文献
72.
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
73.
Snell-Johns Jessica; Mendez Julia L.; Smith Bradley H. 《Canadian Metallurgical Quarterly》2004,18(1):19
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
74.
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
75.
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
76.
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
77.
78.
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
79.
80.
Granularity is a well known concept in parallel processing. While intuitively, the distinction between coarse-grain and fine-grain paralellism is clear, there is no rigorous definition. This paper develops two notions of granularity, each defined formally and represented by a single rational number. The two notions are compared and contrasted with each other and with previously proposed definitions of granularity.Supported, in part, by NSA OCREAE Grant MDA904-85-H-0002. Currently on leave at the National Science Foundation. 相似文献