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   368725篇
  免费   4797篇
  国内免费   2324篇
电工技术   6520篇
综合类   642篇
化学工业   49364篇
金属工艺   15726篇
机械仪表   11186篇
建筑科学   8150篇
矿业工程   1724篇
能源动力   9526篇
轻工业   27690篇
水利工程   3631篇
石油天然气   6385篇
武器工业   58篇
无线电   47380篇
一般工业技术   75227篇
冶金工业   74617篇
原子能技术   8684篇
自动化技术   29336篇
  2021年   2762篇
  2020年   2089篇
  2019年   2645篇
  2018年   4530篇
  2017年   4607篇
  2016年   4885篇
  2015年   3281篇
  2014年   5622篇
  2013年   15987篇
  2012年   9217篇
  2011年   12908篇
  2010年   10145篇
  2009年   11862篇
  2008年   12351篇
  2007年   12598篇
  2006年   10972篇
  2005年   10136篇
  2004年   9952篇
  2003年   9600篇
  2002年   9062篇
  2001年   9451篇
  2000年   8832篇
  1999年   9503篇
  1998年   25050篇
  1997年   17281篇
  1996年   13318篇
  1995年   9758篇
  1994年   8567篇
  1993年   8550篇
  1992年   5852篇
  1991年   5625篇
  1990年   5436篇
  1989年   5244篇
  1988年   4806篇
  1987年   4181篇
  1986年   4198篇
  1985年   4578篇
  1984年   4183篇
  1983年   3853篇
  1982年   3655篇
  1981年   3673篇
  1980年   3546篇
  1979年   3255篇
  1978年   3244篇
  1977年   3644篇
  1976年   5004篇
  1975年   2694篇
  1974年   2637篇
  1973年   2625篇
  1972年   2201篇
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
41.
Lobster krill (Munida genus) represents an under‐valued crustacean frequently caught on European fishing banks. In this work, its sensory, microbiological and biochemical qualities were evaluated during chilled storage. Additionally, the effects of a prestorage antimelanosic treatment consisting of soaking in sodium metabisulphite (SMB) solutions at two different concentrations (0.25% and 0.75%) were also studied. SMB prestorage treatment provided lobster specimens that still exhibited acceptable sensory quality after 10 days of storage, while control specimens were unacceptable at that time. SMB treatment also resulted in a significant (P < 0.05) inhibition of microbial growth, mainly of Enterobacteriaceae, psychrotrophes and proteolytic bacteria. Low lipid oxidation levels were observed for all batches; however, a significantly higher (P < 0.05) retention of polyunsaturated fatty acids was found in SMB‐treated lobster, especially in the 0.75% SMB batch. The results presented here open the way to the potential commercialisation of currently under‐utilised lobster krill as a chilled product.  相似文献   
42.
Fefelov  S. A.  Kazakova  L. P.  Bogoslovskiy  N. A.  Bylev  A. B.  Yakubov  A. O. 《Semiconductors》2020,54(4):450-453
Semiconductors - The current–voltage characteristics measured on Ge2Sb2Te5 thin films in the current mode are studied. The effect of multilevel recording is established when applying...  相似文献   
43.
Journal of Communications Technology and Electronics - Abstract—The article considers the two-dimensional diffraction problem of a TM-type plane electromagnetic wave on a cylindrical silver...  相似文献   
44.
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   
45.
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   
46.
47.
48.
49.
50.
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   
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