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   1798篇
  免费   59篇
电工技术   97篇
综合类   2篇
化学工业   430篇
金属工艺   31篇
机械仪表   27篇
建筑科学   65篇
矿业工程   3篇
能源动力   26篇
轻工业   278篇
水利工程   10篇
石油天然气   5篇
无线电   120篇
一般工业技术   242篇
冶金工业   360篇
原子能技术   27篇
自动化技术   134篇
  2022年   17篇
  2021年   26篇
  2020年   26篇
  2019年   14篇
  2018年   20篇
  2017年   31篇
  2016年   40篇
  2015年   17篇
  2014年   33篇
  2013年   56篇
  2012年   45篇
  2011年   92篇
  2010年   39篇
  2009年   53篇
  2008年   67篇
  2007年   72篇
  2006年   41篇
  2005年   56篇
  2004年   33篇
  2003年   37篇
  2002年   40篇
  2001年   25篇
  2000年   29篇
  1999年   32篇
  1998年   74篇
  1997年   46篇
  1996年   42篇
  1995年   36篇
  1994年   32篇
  1993年   29篇
  1992年   29篇
  1991年   19篇
  1990年   24篇
  1989年   19篇
  1988年   15篇
  1987年   23篇
  1985年   18篇
  1984年   16篇
  1982年   14篇
  1981年   15篇
  1979年   16篇
  1978年   15篇
  1977年   19篇
  1976年   27篇
  1975年   15篇
  1974年   22篇
  1973年   19篇
  1971年   18篇
  1970年   19篇
  1966年   21篇
排序方式: 共有1857条查询结果,搜索用时 62 毫秒
71.
This article presents a meta-analysis of research on evaluative conditioning (EC), defined as a change in the liking of a stimulus (conditioned stimulus; CS) that results from pairing that stimulus with other positive or negative stimuli (unconditioned stimulus; US). Across a total of 214 studies included in the main sample, the mean EC effect was d = .52, with a 95% confidence interval of .466–.582. As estimated from a random-effects model, about 70% of the variance in effect sizes were attributable to true systematic variation rather than sampling error. Moderator analyses were conducted to partially explain this variation, both as a function of concrete aspects of the procedural implementation and as a function of the abstract aspects of the relation between CS and US. Among a range of other findings, EC effects were stronger for high than for low contingency awareness, for supraliminal than for subliminal US presentation, for postacquisition than for postextinction effects, and for self-report than for implicit measures. These findings are discussed with regard to the procedural boundary conditions of EC and theoretical accounts about the mental processes underlying EC. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
72.
The use of supercritical water as coolant/moderator may induce oscillations in the supercritical light water reactor similar to the density wave oscillations observed in boiling water reactors (BWRs). In order to experimentally investigate the stability of supercritical reactors, a fluid-to-fluid downscaled facility is proposed. It is found that with an appropriate mixture of refrigerants R-125 and R-32, the dimensionless enthalpy and density of the supercritical water can be accurately matched for all relevant operational conditions of the reactor. Moreover, the inertia distribution, the friction factor distribution and the heat transfer mechanism are taken into account in the modeling. As a result of the proposed downscaling, the operational pressure, temperature and power are considerably smaller than those of a water-based system, which in turn helps reducing the construction and operational costs of a test facility. Finally, it is found that the often used modeling fluid supercritical CO2 cannot accurately represent supercritical water at reactor conditions.  相似文献   
73.
In the present study, we investigate the two-dimensional laminar flow through a one-sided constriction of a plane channel with a ratio of h:H=1:4 (where h is the step height and H is the channel height). The computational approach employed is based on a mixed implicit/explicit time discretization scheme together with a highly accurate spatial discretization using a P N P N–2 spectral-element method. It is well known that this so-called forward-facing step (FFS) flow exhibits a singularity in the pressure and the velocity derivatives at the corner point. We account for this singularity by a geometric mesh refinement strategy that was proposed in a hp-FEM context. A detailed numerical study of the FFS flow reveals that length and height of the recirculation zone in front of the step are almost constant for creeping flow. In the limit of high Reynolds numbers the length and height of the recirculation zone increase proportional to Re 0.6 and Re 0.2, respectively.  相似文献   
74.
Ohne ZusammenfassungMit 47 AbbildungenDie vorliegende Arbeit ist ein Auszug aus der Dissertation des Verfassers (Technische Hochschule Aachen 1956/57).  相似文献   
75.
By complementation screening of a cadmium-sensitive Schizosaccharomyces pombe mutant deficient in phytochelatin synthesis, but with 44% of the wild-type glutathione content, we cloned a DNA fragment involved in phytochelatin synthesis. Sequence analysis revealed that it encodes the second enzyme involved in glutathione (GSH) biosynthesis, glutathione synthetase (GSH2) (E.C.6.3.2.3, Wang and Oliver, 1997). The mutant allele shows a single base-pair exchange at the 3' end of the reading frame leading to a single amino acid change from glycine to aspartate. This mutation leads to a significant reduction of phytochelatin synthesis, whereas glutathione synthesis is impaired to a far lesser extent. Complementation with the Arabidopsis thaliana GSH2 cDNA led to a partial restoration of phytochelatin synthesis. These data strongly suggest that the GSH2 gene encodes a bifunctional enzyme that is able to catalyse both the synthesis of GSH by adding glycine to the dipeptide (gammaGlu-Cys) and the synthesis of phytochelatins. The sequence has been submitted to EMBL, Accession No. Y08414.  相似文献   
76.
It has been well established that the cytoskeleton is an essential modulator of cell morphology and motility, intracytoplasmic transport and mitosis, however cytoskeletal linkage to the organelles has not been unequivocally demonstrated. Indeed, cytoskeleton appears to be essential in determining and modulating gene phenotype as a function of cellular environment. According to recent studies, the organization of the cytoskeleton network together with associated protein(s) could be essential in regulating mitochondrial function and particularly the permeability of the mitochondrial outer membrane to ADP. The aim of this chapter is to summarize the main properties of the cytoskeletal environment of mitochondria and the possible role(s) of this network in mitochondrial function in myocytes.  相似文献   
77.
78.
R Hierner  K Wilhelm  B Brehl 《Canadian Metallurgical Quarterly》1998,30(3):196-202; discussion 203-5
Distraction-lengthening technique is quite useful in a variety of congenital hand deformities with hypoplastic, or primary normal but secondary shortened (constriction ring syndrome) finger rays. It appears that around the age of two years is the earliest practical time to start distraction; certainly distraction and secondary surgical procedures to improve function should be completed before school entry age whenever possible. Between June 1990 and March 1993, nine distraction lengthening procedures (5 thumbs, 1 index, 3 little fingers) in five patients presenting with congenital hand deformities, were carried out. Although restoring length to the finger, lengthening does not provide normal circumference or, of course, interphalangeal joint motion. Amelioration in function seems to be more important than the esthetic gain. Distraction lengthening tolerates only few errors of indication, operative technique, and/or postoperative management. A high compliance of the patient and her/his parents as well as a close follow-up by an experienced surgeon, are mandatory for a good result. A variety of possible complications have been described. Generally, complication risk increases in cases of simultaneous and multiple level lengthening. Provided adequate operative technique and postoperative care, superficial pin infection and fracture in the region of distraction are the major complications. Contrary to adults, sufficient bone formation by distraction is the rule in children. Therefore, the distraction-lengthening technique is preferred to the distraction-interposition technique in the treatment of congenital hand deformities. The latter should only be used as a salvage procedure in the rare cases of insufficient callus formation. Because of the missing growth potential and reduced joint mobility, distraction lengthening is the therapy of second choice when compared to microvascular second toe transplantation.  相似文献   
79.
Rosin and hydroxymethyl derivatives of rosin acids react rapidly with commercially available glycidyl ethers to give the hydroxy monoesters of aliphatic ethers. These esters of rosin, oxonated rosin and tetrahydroabietic acid are viscous liquids of low acid number and high hydroxyl number with a light to golden amber color. In the case of 12-hydroxymethyltetrahydroabietic acid, the products are colorless gums of a tacky, semisolid consistency. The acid, hydroxyl and saponification values, and the viscosities and softening points are tabulated. So. Utiliz. Res. Dev. Div., ARS, USDA  相似文献   
80.
Beschreibung der Versuchsapparatur zur Messung der Thermospannung der Kette Rh |T + Δ AIN |T Rh für Temperatur-differenzen bis zu ± 60 °C zwischen 1350 und 1650 °C. Ermittlung der Thermokraft und ihres homogenen Anteils. Berechnung der Überführungswärme der wandernden Ionen aus der homogenen Thermokraft. Erörterung zum Leitungsmechanismus im Aluminiumnitrid AlN.  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