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   289726篇
  免费   3663篇
  国内免费   1493篇
电工技术   4953篇
综合类   600篇
化学工业   40785篇
金属工艺   11764篇
机械仪表   8580篇
建筑科学   6771篇
矿业工程   1620篇
能源动力   7093篇
轻工业   22589篇
水利工程   3104篇
石油天然气   5828篇
武器工业   44篇
无线电   34006篇
一般工业技术   56849篇
冶金工业   51075篇
原子能技术   7585篇
自动化技术   31636篇
  2021年   2200篇
  2019年   2108篇
  2018年   3625篇
  2017年   3715篇
  2016年   3959篇
  2015年   2530篇
  2014年   4631篇
  2013年   12273篇
  2012年   7893篇
  2011年   12792篇
  2010年   8699篇
  2009年   9769篇
  2008年   9800篇
  2007年   9748篇
  2006年   8283篇
  2005年   7857篇
  2004年   7844篇
  2003年   7660篇
  2002年   7076篇
  2001年   7167篇
  2000年   6723篇
  1999年   6838篇
  1998年   16421篇
  1997年   11643篇
  1996年   8957篇
  1995年   6916篇
  1994年   6063篇
  1993年   6063篇
  1992年   4404篇
  1991年   4188篇
  1990年   4086篇
  1989年   4085篇
  1988年   3761篇
  1987年   3397篇
  1986年   3407篇
  1985年   3746篇
  1984年   3485篇
  1983年   3232篇
  1982年   3030篇
  1981年   3045篇
  1980年   3031篇
  1979年   2831篇
  1978年   2871篇
  1977年   3146篇
  1976年   4100篇
  1975年   2417篇
  1974年   2382篇
  1973年   2397篇
  1972年   2019篇
  1971年   1781篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Powder Metallurgy and Metal Ceramics - The infiltration of aluminum melts into porous metal skeletons produced by powder metallurgy methods, including 3D printing, under a pressure gradient was...  相似文献   
42.
Upper Barremian – Lower Aptian inner platform “Urgonian” limestones in the Mont de Vaucluse region, SE France, consist of alternating metre-scale microporous and tight intervals. This paper focuses on the influence of structural deformation on the reservoir properties of the Urgonian limestone succession in a study area near the town of Rustrel. Petrographic, petrophysical and structural data were recovered from five fully-cored boreholes, from the walls of a 100 m long underground tunnel, and from a 50 m long transect at a nearby outcrop. The data allowed reservoir property variations in the Urgonian limestones to be studied from core to reservoir scale. Eleven Reservoir Rock Types (RRTs) were identified based on petrographic features (texture, grain size), reservoir properties (porosity, permeability), and the frequency of structural discontinuities such as fractures, faults and stylolites. Tight and microporous reservoir rock types were distinguished. Tight reservoir rock types were characterised by early cementation of intergranular pore spaces and by the presence of frequent structural discontinuities. By contrast microporous reservoir rock types contained preserved intragranular microporosity and matrix permeability, but had very few structural discontinuities. Observed vertical alternations of microporous and tight rock types are interpreted to have been controlled by the early diagenesis of the Urgonian carbonates. Deformation associated with regional-scale tectonic phases, including Albian – Cenomanian “Durancian” uplift (∼105 to 96 Ma) and Pyrenean compression (∼55 to 25 Ma), resulted in the modification of the initial petrophysical properties of the Urgonian limestones. An early diagenetic imprint conditioned both the intensity of structural deformations and the associated circulations of diagenetic and meteoric fluids. Evolution of the Reservoir Rock Types is therefore linked both to the depositional conditions and to subsequent phases of structural deformation.  相似文献   
43.
44.
45.
46.
Interaction of molybdenyl(VI) bis(acetylacetonate) with polyphenylsiloxane in xylene and under mechanochemical activation conditions has been investigated. The interaction in solution proceeds with splitting of the siloxane bond and formation of polymolybdenum(VI) phenylsiloxane with different silicon/metal ratios. The fractions with the silicon/metal ratio < 2 are characterized with high degree of crystallinity and low solubility, whereas those with the ratio > 2 are amorphous. The interaction of the above reagents under mechanical activation conditions proceeds with the formation of soluble polymers similar to those obtained in a solution with the silicon/molybdenum ratio equal to 2.6. The crystal chemistry parameters of the fraction obtained in solution with the ratio Si/Mo equals to 1:2 have been calculated on the basis of the X-ray diffraction analysis data using the Debye–Shearer equation. It has been demonstrated that the chain cross section found using the Miller–Boyer method coincides with that calculated geometrically on the basis of literature data on bond lengths and angles. It is shown that the interaction of molybdenyl(VI) bis(acetylacetonate) with polyphenylsiloxane takes place in solution more deeply than under the conditions of mechanochemical activation and is accompanied by the process of separation siloxanes connection. This leads to the formation of a fraction with smaller ratio of substances than the initial ratio.  相似文献   
47.
48.
49.
50.
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