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   553945篇
  免费   6488篇
  国内免费   1772篇
电工技术   10135篇
综合类   439篇
化学工业   81626篇
金属工艺   22060篇
机械仪表   17754篇
建筑科学   12245篇
矿业工程   3178篇
能源动力   15289篇
轻工业   41634篇
水利工程   5965篇
石油天然气   10684篇
武器工业   23篇
无线电   65902篇
一般工业技术   111671篇
冶金工业   105175篇
原子能技术   12473篇
自动化技术   45952篇
  2021年   5024篇
  2020年   3781篇
  2019年   4882篇
  2018年   8240篇
  2017年   8273篇
  2016年   8778篇
  2015年   5624篇
  2014年   9293篇
  2013年   26539篇
  2012年   14937篇
  2011年   20231篇
  2010年   16130篇
  2009年   18259篇
  2008年   18688篇
  2007年   18473篇
  2006年   16403篇
  2005年   14830篇
  2004年   14098篇
  2003年   14026篇
  2002年   13119篇
  2001年   13116篇
  2000年   12482篇
  1999年   13020篇
  1998年   33261篇
  1997年   23061篇
  1996年   17790篇
  1995年   13164篇
  1994年   11743篇
  1993年   11576篇
  1992年   8511篇
  1991年   8022篇
  1990年   7845篇
  1989年   7578篇
  1988年   7229篇
  1987年   6362篇
  1986年   6139篇
  1985年   6977篇
  1984年   6379篇
  1983年   5851篇
  1982年   5303篇
  1981年   5519篇
  1980年   5031篇
  1979年   5026篇
  1978年   5011篇
  1977年   5677篇
  1976年   7533篇
  1975年   4315篇
  1974年   4075篇
  1973年   4147篇
  1972年   3437篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
To eliminate potential "backward" priming effects, S. Glucksberg et al (see record 1986-29080-001) introduced a variant of the cross-modal lexical priming task in which subjects made lexical decisions to nonword targets that were modeled on a word related to either the contextually biased or unbiased sense of an ambiguous word. Lexical decisions to nonwords were longer than controls only when the nonword was related to the contextually biased sense of the ambiguous word, leading Glucksberg et al to conclude that context does constrain lexical access and that the multiple access pattern observed in previous studies was probably an artifact of backward priming. We did not find nonword interference when the nonword targets used by Glucksberg et al were preceded by semantically related ambiguous or unambiguous word primes. However, we did replicate their sentence context results when the ambiguous words were removed from the sentences. We conclude that the interference obtained by Glucksberg et al is due to postlexical judgments of the congruence of the sentence context and the target, not to context constraining lexical access. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
992.
993.
The kinetics of the reaction of acetic acid and acetylene over zinc acetate-activated carbon catalyst was investigated over a wide range of process variables in a pilot reactor. Although various catalytic reaction mechanisms were postulated, the rate of reaction was most satisfactorily correlated by a mechanism of surface reaction between charged adsorbed acetic acid and acetylene, which assumes that the rate controlling step was the irreversible charged adsorption of acetylene and acetic acid.  相似文献   
994.
A beta-silicon carbide powder with a surface area of 30m2g?l and a mean particle size of < 1μm was produced from the thermal conversion of silicon resin in an atmosphere of hydrogen. The amount of product increased with increasing iron content (0–2.1 wt%) and firing temperature (1200–1500°C). Chemical analysis, X-ray diffraction and i.r. absorption spectrometry were used to follow the conversion reaction.  相似文献   
995.
996.
997.
This paper describes the dependence of constriction resistance on signal frequency. This dependence was calculated for circular constrictions ranging in diameter from 10 to 100 /spl mu/m, and for frequencies ranging from dc to 1 GHz. The results indicate that the magnitude of constriction resistance does not deviate appreciably from values predicted by Holm's classical analytical expression, as long as the skin depth is large compared with the constriction radius. For skin depths that are much smaller than the constriction radius, constriction resistance decreases with increasing frequency to an apparent limiting value independent of the constriction radius. At high frequencies, constriction resistance constitutes only one of two components of the total connection resistance measured in practice. The second component of connection resistance is determined by details of the geometry and dimensions of the contact interface, and increases with signal frequency.  相似文献   
998.
Earlier work on the low temperature solution polyamidation of bisacid A2 has raised a number of structural problems. Work carried out more recently showed that the problem of apparent nonisostoichiometry could be reasonably satisfactorily explained. The present paper reports the synthesis and investigates the properties of a further series of polyamides based upon Bisacid A2. More importantly, however, a detailed characterization and evaluation of the new polymers with respect to their structures is presented. This enabled us to compare the various structures in the light of the experimental evidence provided by a number of analytical and spectroscopic techniques, solution behavior, molecular weight, and thermal, morphological, and mechanical properties. Some work was also done on the effect of incorporating a small amount of a trifunctional monomer into the polyamide system.  相似文献   
999.
Mössbauer studies of Fe2+ in water-soaked nafion polymer membranes in the temperature range between 90 K and 250 K have been performed. Above a critical temperature (~ 180 K) the spectra exhibit both elastic narrow absorption lines and quasielastic broad lines. These spectra are typical of bounded diffusion phenomena observed by Mössbauer spectroscopy in macromolecular systems like haemoglobin, myoglobin and ferritin. Similar spectral shapes have been observed by quasielastic neutron scattering from water in nafion membranes. Within 50 K above the critical temperature the total Mössbauer absorption area decreases by an order of magnitude whereas the narrow absorption line decreases by two orders of magnitude. The results are interpreted in terms of bounded diffusive motion of the iron. Using a model based on overdamped harmonically bound Brownian motion, the essential parameters of the iron motion can be derived as a function of temperature. The iron motion most probably reflects the motion of a large Fe2+ complex, e.g. Fe(H2O)2+6, which is attached to the polymer side chains via the sulphonic group.  相似文献   
1000.
Translated from Atomnaya Énergiya, Vol. 67, No. 2, pp. 81–83, August, 1989.  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