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   285002篇
  免费   3524篇
  国内免费   807篇
电工技术   5007篇
综合类   161篇
化学工业   44181篇
金属工艺   11886篇
机械仪表   8558篇
建筑科学   6696篇
矿业工程   1833篇
能源动力   6735篇
轻工业   25387篇
水利工程   3182篇
石油天然气   7006篇
武器工业   16篇
无线电   31427篇
一般工业技术   56911篇
冶金工业   51361篇
原子能技术   7532篇
自动化技术   21454篇
  2021年   2074篇
  2018年   3672篇
  2017年   3620篇
  2016年   3903篇
  2015年   2464篇
  2014年   4230篇
  2013年   12017篇
  2012年   6825篇
  2011年   9213篇
  2010年   7565篇
  2009年   8642篇
  2008年   8929篇
  2007年   8812篇
  2006年   7828篇
  2005年   7310篇
  2004年   6801篇
  2003年   6554篇
  2002年   6627篇
  2001年   6499篇
  2000年   6177篇
  1999年   6229篇
  1998年   14751篇
  1997年   11029篇
  1996年   8567篇
  1995年   6448篇
  1994年   5839篇
  1993年   5708篇
  1992年   4401篇
  1991年   4392篇
  1990年   4223篇
  1989年   4213篇
  1988年   4173篇
  1987年   3530篇
  1986年   3550篇
  1985年   4089篇
  1984年   3900篇
  1983年   3554篇
  1982年   3366篇
  1981年   3495篇
  1980年   3374篇
  1979年   3308篇
  1978年   3406篇
  1977年   3867篇
  1976年   4990篇
  1975年   3114篇
  1974年   2969篇
  1973年   2988篇
  1972年   2621篇
  1971年   2432篇
  1970年   2053篇
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
31.
32.
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   
33.
34.
Theoretical Foundations of Chemical Engineering - A set of measures to establish the technology for manufacturing highly active sources of γ radiation with an active part from...  相似文献   
35.
Metallurgical and Materials Transactions B - The quality requirements of aluminum products are steadily increasing, and the presence of non-metallic inclusions have a large impact on the quality of...  相似文献   
36.
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   
37.
38.
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   
39.
40.

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