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   32272篇
  免费   1600篇
  国内免费   36篇
电工技术   351篇
综合类   57篇
化学工业   7044篇
金属工艺   607篇
机械仪表   583篇
建筑科学   1906篇
矿业工程   81篇
能源动力   884篇
轻工业   2719篇
水利工程   301篇
石油天然气   165篇
武器工业   3篇
无线电   2305篇
一般工业技术   5990篇
冶金工业   5311篇
原子能技术   213篇
自动化技术   5388篇
  2023年   277篇
  2022年   451篇
  2021年   702篇
  2020年   506篇
  2019年   595篇
  2018年   726篇
  2017年   693篇
  2016年   910篇
  2015年   818篇
  2014年   1033篇
  2013年   1939篇
  2012年   1683篇
  2011年   2139篇
  2010年   1518篇
  2009年   1477篇
  2008年   1772篇
  2007年   1663篇
  2006年   1461篇
  2005年   1241篇
  2004年   1103篇
  2003年   952篇
  2002年   920篇
  2001年   555篇
  2000年   536篇
  1999年   539篇
  1998年   527篇
  1997年   464篇
  1996年   474篇
  1995年   448篇
  1994年   434篇
  1993年   443篇
  1992年   386篇
  1991年   233篇
  1990年   322篇
  1989年   324篇
  1988年   275篇
  1987年   300篇
  1986年   290篇
  1985年   311篇
  1984年   275篇
  1983年   259篇
  1982年   244篇
  1981年   212篇
  1980年   181篇
  1979年   185篇
  1978年   170篇
  1977年   143篇
  1976年   129篇
  1975年   138篇
  1974年   110篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
This study examined the relationship between alliance and retention in family therapy. Alliance was examined at the individual (parent and adolescent) and family levels (within-family differences). Participants were 34 families who received functional family therapy for the treatment of adolescent (aged 12-18 years) behavior problems. Families were classified as treatment dropouts (n=14) or completers (n=20). Videotapes of the first sessions were rated to identify parent and adolescent alliances with the therapist. Results demonstrated that individual parent and adolescent alliances did not predict retention. However, as hypothesized, dropout cases had significantly higher unbalanced alliances (parent minus adolescent) than did completer cases. These findings highlight the importance of alliances in functional family therapy and suggest that how the alliance operates in conjoint family therapy may be a function of systemic rather than of individual processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
152.
Ion exchanged CoNaY was sulfided at 473 and 673 K and subsequently heated in He at 673 and 773 K. The resulting samples were characterized by means of overall sulfur analysis, temperature programmed Ar treatment and Fourier transform infrared spectroscopy. It was shown that during He flushing at sufficiently high temperature a protolysis reaction occurs resulting in the decomposition of Co sulfide into Co2+ ions and H2S.  相似文献   
153.
154.
155.
156.
Impossible and ambiguous shading patterns   总被引:2,自引:1,他引:1  
A smooth object depicted in a monochrome image will often exhibit brightness variation, or shading. A problem much studied in computer vision has been that of how object shape may be recovered from image shading. When the imaging conditions are such that an overhead point-source illuminates a smooth Lambertian surface, the problem may be formulated as that of finding a solution to an eikonal equation. This article will focus on the existence and uniqueness of such solutions, reporting recent results obtained. With regard to existence, shading patterns are exhibited for which there is no corresponding object shape. Specifically, a necessary and sufficient condition is presented for a circularly symmetric eikonal equation to admit exclusively unbounded solutions; additionally, a sufficient condition is given for an eikonal equation to have no solution whatsoever. In connection with uniqueness, we consider eikonal equations, defined over a disc, such that the Euclidean norm of the gradient of any solution is circularly symmetric, vanishes exactly at the disc center, and diverges to infinity as the circumference of the disc is approached. Contrary to earlier influential work, a class of such eikonal equations is shown to possess simultaneously circularly symmetric and noncircularly symmetric bounded smooth solutions.  相似文献   
157.
158.
As developed by Wallace and Dadda, a method for high-speed, parallel multiplication is to generate a matrix of partial products and then reduce the partial products to two numbers whose sum is equal to the final product. The resulting two numbers are then summed using a fast carry-propagate adder. This paper presents Reduced Area multipliers, which employ a modified reduction scheme that results in fewer components and less interconnect overhead than either Wallace or Dadda multipliers. This reduction scheme is especially useful for pipelined multipliers, because it minimizes the number of latches required in the reduction of the partial products. The reduction scheme can be applied to either unsigned (sign-magnitude) or two's complement numbers. Equations are given for determining the number of components and a method is presented for estimating the interconnect overhead for Wallace, Dadda, and Reduced Area multipliers. Area estimates indicate that for non-pipelined multipliers, the reduction in area achieved with Reduced Area multipliers ranges from 3.7 to 6.6 percent relative to Dadda multipliers, and from 3.8 to 8.4 percent relative to Wallace multipliers. For fully pipelined multipliers, the reduction in area ranges from 15.1 to 33.6 percent relative to Dadda multipliers, and from 2.9 to 9.0 percent relative to Wallace multipliers.  相似文献   
159.
Heat Transport to the Wall of Packed Tubes. Radial conduction of heat in packed tubes has a crucial influence on yield and selectivity of many heterogeneously catalyzed reactions. In spite of many years of intensive research in the field, there are still tremendous discrepancies between correlations of different origin. Even the standard model using two constant heat transport parameters, which was introduced in the fifties and has since become most widely accepted, has been controversially discussed and called into question. The unsatisfactory state of the art has been an incentive for several groups of researchers to take up this old topic once again. Three parallel experimental investigations on heat transport with air flowing in packed tubes of similar dimensions, electrically heated, steam-heated, or water-cooled, were completed in 1991. Comparative evaluation of the results of these three investigations, together with other data from the relevant literature, now provides the first clear answers to some of the questions so controversially discussed in the past.  相似文献   
160.
Terrorism: A Reference Handbook, Stephen Atkins, Santa Barbara, ABC-CLIO (1992), 199 pp. Terrorism: Roots, Impact, Responses, Lawrence Howard (Ed.), Prager, New York (1992), 193 pp. Hostage-Taking Terrorism: Incident Response Strategy, Alastair MacWillson, St Martins, New York (1992), 263 pp.  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