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   1521130篇
  免费   26142篇
  国内免费   6999篇
电工技术   34491篇
综合类   6385篇
化学工业   272239篇
金属工艺   64753篇
机械仪表   43371篇
建筑科学   46119篇
矿业工程   11497篇
能源动力   50381篇
轻工业   111881篇
水利工程   15490篇
石油天然气   37876篇
武器工业   132篇
无线电   197562篇
一般工业技术   287038篇
冶金工业   170918篇
原子能技术   34191篇
自动化技术   169947篇
  2021年   15618篇
  2020年   11905篇
  2019年   14675篇
  2018年   16921篇
  2017年   16405篇
  2016年   21881篇
  2015年   17465篇
  2014年   28742篇
  2013年   87922篇
  2012年   35907篇
  2011年   49074篇
  2010年   43416篇
  2009年   51763篇
  2008年   45366篇
  2007年   42774篇
  2006年   44606篇
  2005年   39779篇
  2004年   41722篇
  2003年   41656篇
  2002年   40489篇
  2001年   37417篇
  2000年   35832篇
  1999年   35172篇
  1998年   48077篇
  1997年   40763篇
  1996年   36261篇
  1995年   31183篇
  1994年   29158篇
  1993年   29086篇
  1992年   26158篇
  1991年   23272篇
  1990年   23647篇
  1989年   22698篇
  1988年   21208篇
  1987年   19479篇
  1986年   18836篇
  1985年   22154篇
  1984年   22329篇
  1983年   20242篇
  1982年   19236篇
  1981年   19377篇
  1980年   17948篇
  1979年   18442篇
  1978年   17704篇
  1977年   17465篇
  1976年   18391篇
  1975年   15974篇
  1974年   15464篇
  1973年   15573篇
  1972年   12990篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
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   
62.
63.
64.
65.
Pinhão seed is an unconventional source of starch and the pines grow up in native forests of southern Latin America. In this study, pinhão starch was adjusted at 15, 20 and 25% moisture content and heated to 100, 110 and 120 °C for 1 h. A decrease in λ max (starch/iodine complex) was observed as a result of increase in temperature and moisture content of HMT. The ratio of crystalline to amorphous phase in pinhão starch was determined via Fourier transform infra red by taking 1045/1022 band ratio. A decrease in crystallinity occurred as a result of HMT. Polarised light microscopy indicated a loss of birefringence of starch granules under 120 °C at 25% moisture content. Granule size distribution was further confirmed via scanning electron microscopy which showed the HMT effects. These results increased the understanding on molecular and structural properties of HMT pinhão starch and broadened its food and nonfood industrial applications.  相似文献   
66.
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   
67.
68.
Programming and Computer Software - Image segmentation using a hierarchical sequence of piecewise constant approximations that minimally differ from the original image in terms of the total squared...  相似文献   
69.
70.

To increase the efficiency of designing systems intended for monitoring surface cracks in aluminum structures during their working life, we have analyzed a two-dimensional symmetric problem on uniaxial extension of an Al-polyimide-Cu layered structure with ideal adhesion between layers and a model crack in the aluminum base. The problem has been first solved for a sample with the crack modeled by a zero-thickness notch using the ANSYS engineering simulation program package. It is shown that this setting of the problem can lead to inadequate results as manifested, in particular, by significantly overstated mechanical stresses in aluminum in the region of crack emergence on the surface. In order to eliminate this difficulty, we propose to use the structure with a model defect in the form of a notch of nonzero thickness in the initial unstressed state of the structure. Recommendations for selecting the thickness of a notch used in the model structure are given.

  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