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   495268篇
  免费   6634篇
  国内免费   2006篇
电工技术   9145篇
综合类   860篇
化学工业   71862篇
金属工艺   19529篇
机械仪表   15524篇
建筑科学   11672篇
矿业工程   2526篇
能源动力   12223篇
轻工业   41198篇
水利工程   5142篇
石油天然气   8977篇
武器工业   107篇
无线电   61177篇
一般工业技术   97958篇
冶金工业   90437篇
原子能技术   11518篇
自动化技术   44053篇
  2021年   3786篇
  2019年   3733篇
  2018年   6827篇
  2017年   7014篇
  2016年   7228篇
  2015年   4586篇
  2014年   7613篇
  2013年   21222篇
  2012年   12512篇
  2011年   17170篇
  2010年   13219篇
  2009年   15136篇
  2008年   16089篇
  2007年   16061篇
  2006年   14143篇
  2005年   14577篇
  2004年   13689篇
  2003年   13078篇
  2002年   12012篇
  2001年   11985篇
  2000年   11399篇
  1999年   11826篇
  1998年   27938篇
  1997年   19988篇
  1996年   15566篇
  1995年   12118篇
  1994年   10696篇
  1993年   10631篇
  1992年   8166篇
  1991年   7641篇
  1990年   7369篇
  1989年   7182篇
  1988年   6729篇
  1987年   5971篇
  1986年   5939篇
  1985年   6773篇
  1984年   6268篇
  1983年   5730篇
  1982年   5440篇
  1981年   5496篇
  1980年   5376篇
  1979年   5064篇
  1978年   4969篇
  1977年   5668篇
  1976年   7201篇
  1975年   4370篇
  1974年   4289篇
  1973年   4364篇
  1972年   3577篇
  1971年   3254篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
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   
72.
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   
73.
74.
75.
Here we report some recent biophysical issues on the preparation of solute-filled lipid vesicles and their relevance to the construction of “synthetic cells.” First, we introduce the “semi-synthetic minimal cells” as the liposome-based cell-like systems, which contain a minimal number of biomolecules required to display simple and complex biological functions. Next, we focus on recent aspects related to the construction of synthetic cells. Emphasis is given to the interplay between the methods of synthetic cell preparation and the physics of solute encapsulation. We briefly introduce the notion of structural and compositional “diversity” in synthetic cell populations.  相似文献   
76.
The viability and β‐galactosidase activity of four Lactobacillus strains in milk drink containing gums during 28 days of refrigerated storage at 4 °C were assessed. The population of Lactobacillus rhamnosus GGB101 and Lactobacillus rhamnosus GGB103 were maintained, whereas the population of Lactobacillus reuteri DSM20016 and Lactobacillus reuteri SD2112 significantly decreased. The recommended level of 6 log CFU g?1 was exceeded for all tested trains throughout storage. The highest viable number of Lactobacillus rhamnosus GGB103 (8.76 ± 0.03 log CFU mL?1) was obtained in the product containing carrageenan–maltodextrin. The addition of guar–locust bean–carrageenan led to 20‐fold increase in the level of β‐galactosidase activity for L. rhamnosus GGB101 (1208 ± 2.12 Miller units mL?1) compared to the control (61 ± 2.83 Miller units mL?1). Our results suggested that gums could be added to milk to improve viability and enhance β‐galactosidase activity of Lactobacillus.  相似文献   
77.
78.
79.
80.
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