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   10476篇
  免费   288篇
  国内免费   14篇
电工技术   142篇
综合类   8篇
化学工业   2393篇
金属工艺   246篇
机械仪表   192篇
建筑科学   452篇
矿业工程   54篇
能源动力   313篇
轻工业   686篇
水利工程   106篇
石油天然气   106篇
无线电   689篇
一般工业技术   1798篇
冶金工业   1863篇
原子能技术   102篇
自动化技术   1628篇
  2022年   112篇
  2021年   150篇
  2020年   121篇
  2019年   119篇
  2018年   163篇
  2017年   164篇
  2016年   202篇
  2015年   176篇
  2014年   256篇
  2013年   717篇
  2012年   396篇
  2011年   501篇
  2010年   375篇
  2009年   410篇
  2008年   454篇
  2007年   397篇
  2006年   390篇
  2005年   333篇
  2004年   305篇
  2003年   258篇
  2002年   263篇
  2001年   186篇
  2000年   179篇
  1999年   170篇
  1998年   244篇
  1997年   197篇
  1996年   181篇
  1995年   146篇
  1994年   156篇
  1993年   145篇
  1992年   134篇
  1991年   114篇
  1990年   114篇
  1989年   144篇
  1988年   102篇
  1987年   121篇
  1986年   122篇
  1985年   138篇
  1984年   161篇
  1983年   120篇
  1982年   119篇
  1981年   96篇
  1980年   93篇
  1979年   100篇
  1978年   83篇
  1977年   103篇
  1976年   99篇
  1975年   88篇
  1974年   92篇
  1973年   76篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Psychology needs a metric for positive mental health that would be analogous to the IQ tests that measure above average intelligence. The Defensive Function Scale of the DSM-IV offers a possible such metric. In the present article the author links the transformational qualities of defenses at the mature end of the Defensive Function Scale (altruism, suppression, humor, anticipation, and sublimation) to positive psychology. First, the methodological problems involved in the reliable assessment of defenses are acknowledged. Next, the use of prospective longitudinal study to overcome such difficulties and to provide more reliable definition and measurement of defenses is outlined. Evidence is also offered that, unlike many psychological measures, the maturity of defenses is quite independent of social class, education, and IQ. Last, evidence is offered to illustrate the validity of mature defenses and their contribution to positive psychology. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
992.
993.
Assembly of functional cytochrome oxidase in yeast requires Cox17, which has been postulated to deliver copper ions to the mitochondrion for insertion into the enzyme. This role for Cox17 is supported by the observation that it binds copper as a binuclear cuprous-thiolate cluster. X-ray absorption spectroscopy, together with UV-visible absorption and emission spectroscopy, indicates the presence of bound cuprous ions, trigonally coordinated by thiolate ligands. Analysis of the EXAFS shows three Cu-S bonds at 2.26 A, plus a short Cu-Cu distance of 2.7 A, indicating a binuclear cluster in Cox17. The cuprous-thiolate cluster in Cox17 is substantially more labile than structurally related clusters in metallothioneins.  相似文献   
994.
This paper details experiments and analyses regarding the phenomenon of liquid discharge into a gaseous atmosphere from the bottom of a vessel with an unvented, upper gas space. The primary goal is the development of a simple model that predicts the rate of liquid discharge under the prevailing unvented condition. A literature survey of previous work on this phenomenon yielded only simple experiments and analyses that were limited in scope. Experiments were subsequently undertaken with an air-water system, using a larger volume and a wide range of drain line diameters. In addition to flowrate data, visual information was acquired regarding the physical mechanism possibly governing the prevalent flow regimes. The governing physical mechanism is identified as the stability of a gas-liquid interface, perturbed by buoyancy, at the drain line entrance. G.I. Taylor's fundamental analysis of interfacial stability lead to the determination of criteria for flow regime transition among the three prevalent flow regimes, corresponding to so-called small, medium, and large diameters. Also, analysis of the growth of interfacial instabilities lead to the application of flooding models for drainage rates within each regime. The models for moderate and large diameters were then compared against data, which confirmed their success in predicting discharge rates under the unvented condition.The motivation for this effort, besides the basic scientific significance of studying such a fundamental phenomenon, was its numerous applications, one of which is commercial nuclear reactor systems. Specifically, the phenomenon prevails in liquid coolant discharge from a PWR pressurizer, with an unvented steam volume, into a steam atmosphere existing in the adjoining hot coolant leg. Such a phenomenon could occur as part of a transient, or severe accident, scenario, entailing saturated conditions and steam production in the normally subcooled primary heat transport loop. The developed model was implemented in the Modular Accident Analysis Program (MAAP), a computer code designed to predict reactor system behavior in response to postulated off-normal conditions, including severe accident scenarios.  相似文献   
995.
Fuel instability reactions are defined in terms of the formation of deleterious products such as filterable sediments and peroxides. Gravimetric stability tests have been carried out at 80°C using two model nitrogen heterocycles: 2,5-dimethy1pyrrole, DMP, and 3-methylindole, 3-MI, in an otherwise stable shale derived middle distillate fuel. Potential interactive effects for these model nitrogen heterocycles have been described by the presence of organic base co-dopants. Organic bases employed included: tri-n-butylamine, N, N-dimethyl-aniline, and 4-dimethylaminopyridine. Simple organic amines exerted only minor interactive effects, usually an increase in filterable sediment in the range of 5-15%. However, the diamine species, 4-dimethylaminopyridine, interacted in a strong positive fashion to generate increased amounts, 22-44%, of sediment.  相似文献   
996.
The Racial Identity Attitude Scale—Long Form (RIAS–L; J. E. Helms & T. A. Parham, 1996) is likely to be the instrument of choice in future research on African American racial identity development, but little is known about its psychometric properties. RIAS-L data from 275 African American community members and students were collected, and a series of analyses (i.e., correlations, multiple regressions, and confirmatory modeling) was conducted to explore convergent and discriminant validity. Overall, results were mixed, generally revealing limited support for the RIAS-L's convergent and discriminant validity and highlighting concerns regarding the Preencounter and Encounter subscales. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
997.
本文主介绍了电镀填孔技术,并探讨了DC和PPR电镀填孔技术的优缺点和影响填孔效果的相关因素。  相似文献   
998.
This paper considers the problem of effective algorithms for some problems having structured coefficient matrices. Examples of such problems include rational approximation and rational interpolation. The corresponding coefficient matrices include Hankel, Toeplitz and Vandermonde-like matrices. Effective implies that the algorithms studied are suitable for implementation in either a numeric environment or else a symbolic environment.The paper includes two algorithms for the computation of rational interpolants which are both effective in symbolic environments. The algorithms use arithmetic that is free of fractions but at the same time control the growth of coefficients during intermediate computations. One algorithm is a look-around procedure which computes along a path of closest normal points to an offdiagonal path while the second computes along an arbitrary path using a look-ahead strategy. Along an antidiagonal path the look-ahead recurrence is closely related to the Subresultant PRS algorithm for polynomial GCD computation. Both algorithms are an order of magnitude faster than alternative methods which are effective in symbolic environments.  相似文献   
999.
A meta-analysis of published studies with adult human participants was conducted to evaluate whether physical fitness attenuates cardiovascular reactivity and improves recovery from acute psychological stressors. Thirty-three studies met selection criteria; 18 were included in recovery analyses. Effect sizes and moderator influences were calculated by using meta-analysis software. A fixed effects model was fit initially; however, between-studies heterogeneity could not be explained even after inclusion of moderators. Therefore, to account for residual heterogeneity, a random effects model was estimated. Under this model, fit individuals showed significantly attenuated heart rate and systolic blood pressure reactivity and a trend toward attenuated diastolic blood pressure reactivity. Fit individuals also showed faster heart rate recovery, but there were no significant differences in systolic blood pressure or diastolic blood pressure recovery. No significant moderators emerged. Results have important implications for elucidating mechanisms underlying effects of fitness on cardiovascular disease and suggest that fitness may be an important confound in studies of stress reactivity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
1000.
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