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   4572篇
  免费   98篇
  国内免费   3篇
电工技术   32篇
综合类   2篇
化学工业   443篇
金属工艺   105篇
机械仪表   51篇
建筑科学   136篇
矿业工程   12篇
能源动力   61篇
轻工业   374篇
水利工程   41篇
石油天然气   11篇
无线电   200篇
一般工业技术   418篇
冶金工业   2477篇
原子能技术   41篇
自动化技术   269篇
  2022年   36篇
  2021年   49篇
  2020年   40篇
  2019年   48篇
  2018年   53篇
  2017年   45篇
  2016年   50篇
  2015年   52篇
  2014年   55篇
  2013年   139篇
  2012年   103篇
  2011年   156篇
  2010年   128篇
  2009年   134篇
  2008年   158篇
  2007年   116篇
  2006年   117篇
  2005年   109篇
  2004年   90篇
  2003年   77篇
  2002年   94篇
  2001年   60篇
  2000年   70篇
  1999年   95篇
  1998年   636篇
  1997年   378篇
  1996年   255篇
  1995年   145篇
  1994年   144篇
  1993年   128篇
  1992年   56篇
  1991年   56篇
  1990年   67篇
  1989年   35篇
  1988年   40篇
  1987年   55篇
  1986年   41篇
  1985年   39篇
  1984年   25篇
  1983年   25篇
  1982年   23篇
  1981年   34篇
  1980年   40篇
  1979年   12篇
  1978年   16篇
  1977年   92篇
  1976年   159篇
  1975年   9篇
  1973年   9篇
  1972年   11篇
排序方式: 共有4673条查询结果,搜索用时 46 毫秒
81.
We retrospectively reviewed electrodiagnostic studies performed on 169 athletes with 190 sports injuries to nerve fibers. Eighty-eight percent of the injuries were to the upper extremity. Athletes participated in 27 sports, but over one third of injuries were sustained playing football. The most common injuries were burners (n = 38) and cervical radiculopathies (n = 18), followed by median (n = 28), axillary (n = 22), ulnar (n = 19), suprascapular (n = 14), and peroneal (n = 11) mononeuropathies. This is the largest reported series of sports-related nerve injuries.  相似文献   
82.
BACKGROUND/AIMS: Chronic graft hepatitis occurs in 20-30% adults after liver transplantation but the prevalence and causes in children are not known. In adults, hepatitis C virus infection is prevalent prior to transplantation and recurrent infection is a frequent cause of graft dysfunction. The significance of the recently described hepatitis G virus infection remains unproven. The aim of this study was to examine the role of hepatitis C virus and hepatitis G virus infection in chronic graft hepatitis after paediatric liver transplantation. METHODS: The prevalence of graft hepatitis and the role of hepatitis C virus and hepatitis G virus infections in 80 children after liver transplantation have been studied, with a median follow up of 4.4 years (range 0.4 to 10.7), and the persistence of hepatitis G infection in the presence of immunosuppression has been determined. RESULTS: Chronic graft hepatitis was diagnosed in 19/80 (24%) children and was most frequently seen in children transplanted for cryptogenic cirrhosis (71%). There was no significant difference in the prevalence of chronic hepatitis in those transplanted before or after donor anti-HCV screening. Hepatitis C infection occurred in three children transplanted prior to donor screening but in only one was associated with chronic hepatitis. Hepatitis G infection was found in 22/79 (28%) transplant recipients but was not associated with graft hepatitis. In 17/21 children hepatitis G infection persisted for a median of 5.2 years after transplantation. CONCLUSION: Chronic hepatitis occurred in 24% of children after liver transplantation, a similar prevalence to that in adults. Cryptogenic liver disease predisposed to graft hepatitis, but neither hepatitis C nor hepatitis G infection was associated. Hepatitis G virus caused a frequent and usually persistent infection after transplantation.  相似文献   
83.
A nurse-driven clinic that uses a client-centered approach evolved from an independent ambulatory care program. The clinic operates 4 to 5 hours per day and provides patient counseling, health care maintenance, primary care, patient education, and therapeutic care.  相似文献   
84.
LS Schlesinger 《Canadian Metallurgical Quarterly》1998,6(2):47-9; discussion 49-50
Accumulated evidence to date confirms the importance of the C3-CR pathway in the phagocytosis of pathogenic mycobacteria. Detailed receptor-ligand studies for phagocytosis are creating the framework to test the hypothesis that the entry pathway for these bacteria influences the immediate host cell response and their intracellular fate. These types of study are particularly important for improving our understanding of the outcome of primary infection in humans, where the number of bacilli is presumed to be very low.  相似文献   
85.
Central and cerebral hemodynamics was studied using echocardiography and transcranial dopplerography in 200 poststroke patients over 60 in the course of 5-year follow-up. It was established that cardiac hypodynamic syndrome, i.e. continuous or paroxysmal fall of minute blood volume below 3 l, is the most significant contributing factor in the onset of cerebral ischemia. Drugs are recommended for prevention of ischemic stroke. Those lowering cardiac hemodynamic reserve should be excluded in patients at high risk of acute failure of cerebral circulation.  相似文献   
86.
Nonsense codons between position 14 within the first exon and position 193 within the penultimate exon of the human gene for triosephosphate isomerase reduce mRNA abundance to 25% of normal. The reduction in abundance is due to the decay of newly synthesized mRNA that copurifies with nuclei. TPI mRNA that copurifies with cytoplasm is immune to decay. We show here that immunity is not due to the failure of nonsense-containing mRNA to form polysomes. This finding indicates that cytoplasmic mRNA, in contrast to nucleus-associated mRNA, may have lost one or more factors that are required for nonsense-mediated decay or gained one or more factors that confer immunity to nonsense-mediated decay.  相似文献   
87.
In response to D. Cicchetti's (see record 1998-01884-002) and W. A. Mason's (see record 1998-01884-003) commentaries, this article scrutinizes infant maltreatment in monkeys and its public health implications. Studies of infant abuse and neglect in monkeys have used operational definitions based on (a) adult behavior or (b) adult behavior and infant outcome (depending on data available for analysis). Direct comparisons between the incidence of maltreatment in monkey and human populations can be only tentative as a result of differences in operational definitions of maltreatment. A simplified version of the ecological-transactional model of maltreatment can be used in research with nonhuman primates, and different species can be used to model different aspects of the human phenomenon. Although abuse and neglect take different forms in animals and humans, research with animal models can make an important contribution to elucidating the adaptive function, if any, of child maltreatment and the proximate mechanisms underlying its occurrence. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
88.
A vertical hot electron transistor incorporating a two-dimensional electron gas (2DEG) base has been fabricated in the GaAs-AlGaAs materials system. The difficulties caused by the need to form selective ohmic contacts to the different conducting layers have been overcome using a combination of in situ focused ion beam (FIB) isolation and molecular beam epitaxial (MBE) regrowth. This has allowed a high yield of working devices to be achieved with a typical common emitter current gain of hFE=6 at low temperatures  相似文献   
89.
A novel chitinase gene of tobacco was isolated and characterized by DNA sequence analysis of a genomic clone and a cDNA clone. Comparative sequence analysis of both clones showed an identity of 94%. The proteins encoded by these sequences do not correspond to any of the previously characterized plant chitinases of classes I-IV and are designated as class V chitinases. Comparison of the chitinase class V peptide sequence with sequences in the Swiss Protein databank revealed significant sequence similarity with bacterial exo-chitinases from Bacillus circulans, Serratia marcescens and Streptomyces plicatus. It was demonstrated that class V chitinase gene expression is induced after treatment of tobacco with different forms of stress, like TMV-infection, ethylene treatment, wounding or ultraviolet irradiation. Two related chitinase class V proteins of 41 and 43 kDa were purified from Samsun NN tobacco leaves inoculated with tobacco mosaic virus. The proteins were purified by Chelating Superose chromatography and gel filtration. In vitro assays demonstrated that class V chitinases have endo-chitinase activity and exhibit antifungal activity toward Trichoderma viride and Alternaria radicina. In addition, it was shown that class V chitinase acts synergistically with tobacco class I beta-1,3-glucanase against Fusarium solani germlings.  相似文献   
90.
Summary Controlled rounding is a procedure that perturbs tabular data collected from respondents in such a way as to preserve the anonymity of the respondents while maintaining the integrity of the data. Controlled rounding techniques are regularly used by the United States Bureau of the Census and its counterparts in other countries. This paper discusses the complexity of the three-dimensional controlled rounding problem. In particular, the three-dimensional, zero-restricted controlled rounding problem is shown to be NP-complete. As zero-restricted controlled roundings may fail to exist, various relaxations of this basic rounding problem have been defined. The paper introduces a sequence of such relaxations and proceeds to address the existence of solutions and complexity issues for the relaxed problems.
Zusammenfassung Die Technik des kontrollierten Rundens (Controlled Rounding) wird von Behörden wie dem United States Bureau of Census benutzt, um in mehrdimensionalen Tabellen oder Matrizen erfaßte statistische Daten durch Approximation so zu verändern, daß sowohl die Anonymität von Einzeldaten (Matrixeinträgen) als auch die Integrität der Gesamtdaten (Zeilensummen, Spaltensummen etc.) gewährleistet ist. In dieser Arbeit behandeln wir die Komplexität und Lösbarkeit des dreidimensionalen Rundungsproblems und diskutieren eine Hierarchie von Relaxationen, die bei Nichtlösbarkeit des Ausgangsproblems alternative, nahezu zulässige Lösungen liefern.
  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