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   176955篇
  免费   2135篇
  国内免费   704篇
电工技术   3291篇
综合类   101篇
化学工业   27898篇
金属工艺   7774篇
机械仪表   5121篇
建筑科学   4410篇
矿业工程   875篇
能源动力   4680篇
轻工业   16402篇
水利工程   1702篇
石油天然气   3126篇
武器工业   2篇
无线电   19846篇
一般工业技术   33317篇
冶金工业   33114篇
原子能技术   4291篇
自动化技术   13844篇
  2021年   1312篇
  2019年   1246篇
  2018年   2096篇
  2017年   2078篇
  2016年   2186篇
  2015年   1570篇
  2014年   2717篇
  2013年   7802篇
  2012年   4549篇
  2011年   6362篇
  2010年   5033篇
  2009年   5882篇
  2008年   5860篇
  2007年   5836篇
  2006年   5009篇
  2005年   4680篇
  2004年   4473篇
  2003年   4143篇
  2002年   4101篇
  2001年   4125篇
  2000年   3922篇
  1999年   4054篇
  1998年   10380篇
  1997年   7390篇
  1996年   5653篇
  1995年   4282篇
  1994年   3617篇
  1993年   3566篇
  1992年   2604篇
  1991年   2539篇
  1990年   2417篇
  1989年   2436篇
  1988年   2378篇
  1987年   2129篇
  1986年   2068篇
  1985年   2369篇
  1984年   2186篇
  1983年   2016篇
  1982年   1883篇
  1981年   1945篇
  1980年   1797篇
  1979年   1817篇
  1978年   1777篇
  1977年   2108篇
  1976年   2689篇
  1975年   1557篇
  1974年   1550篇
  1973年   1607篇
  1972年   1353篇
  1971年   1262篇
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
151.
The results of the thermal solution of oil shale in benzene in a flow unit under supercritical conditions are reported. It was found that the conversion of shale organic matter into liquid products increased by a factor of 2.5 with an increase in the solvent pressure from 5 to 15 MPa.  相似文献   
152.
Hot filament and microwave plasma CVD micro- nanocrystalline diamond films are analysed by visible and ultra-violet excitation source Raman spectroscopy. The sample grain size varies from 20 nm to 2 μm. The hydrogen concentration in samples is measured by SIMS and compared to the grain size, and to the ratio of sp2 carbon bonds determined by Raman spectroscopy from the 1332 cm 1 diamond peak and the sp2 1550 cm 1 G band. Hydrogen concentration appears to be proportional to the sp2 bonds ratio. The 3000 cm 1 CHx stretching mode band intensity observed on the Raman spectra is decreasing with the G band intensity. Thermal annealing modifies the sp2 phase structure and concentration, as hydrogen outdiffuses.  相似文献   
153.
154.
The main rules and principles which govern the choice of new variants for chemical technology of combined processing of titanium-rare-metal raw materials are considered. The existing variants of the technology are characterized from the viewpoint of their technological, economical, and ecological efficiency and social importance for a given region. A realistic choice of a technology from a large number of available variants should take into account the entire combination of their advantages and disadvantages The implementation of a rational technological scheme will result in the creation of economically profitable and efficient domestic production satisfying the demands of Russian industry in rare-metal and titanium materials. Directions are noted in which it is expedient to continue studies on designing a rational technology of loparite concentrate or some other concentrate.  相似文献   
155.

Background  

Bioelectrical Impedance (BIA) derived phase angle is increasingly being used as an objective indicator of nutritional status in advanced cancer. Subjective Global Assessment (SGA) is a subjective method of nutritional status. The objective of this study was to investigate the association between BIA derived phase angle and SGA in advanced colorectal cancer.  相似文献   
156.
157.
The use of damage-sensitive features to evaluate structural condition or health is a very critical aspect of structural health monitoring. The purpose of this paper is to investigate the potential of two different damage-sensitive features for detecting damage. Different damage scenarios are simulated on a large-scale laboratory structure and a three-span highway bridge for demonstration. The features presented in this paper are the modal flexibility-based deflection and curvature both of which are obtained directly from dynamic properties. In the literature, flexibility associated with mode shapes and mode shapes curvatures have been mostly explored. In this study, multi-input–multi-output dynamic data are used to obtain modal flexibility, which is a close approximation to the actual flexibility. A main novelty is that the curvature is calculated from the deflected shapes using the modal flexibility as opposed to using modal vectors. In this paper, the theory of the methodology is explained and then experimental studies and results are presented. For the experimental studies, the laboratory specimen and the three-span bridge were gradually damaged. It is shown that both deflection and curvature are conceptual and physically meaningful features for damage detection and localization. The issues and the requirements for these features to perform successfully are also presented.  相似文献   
158.
A new type of a single-axis azimuthal tracker is presented. The novel feature of this tracker is the ability to move the collector’s plane in two directions through a special support structure. This structure consists of a sliding mechanism on the central axis and a curved window on the cylindrical surface coaxial to the central axis. Consequently, the proposed novel heliotrope behaves similarly to a two-axis tracker. Two different windows designed on the cylindrical surface may be used to provide very high efficiencies throughout a year. Several performance measurements have been conducted on this novel tracker, a polar tracker and the reference two-axis tracker. Pyranometers, appropriately calibrated, were installed on all three systems to record the global incoming irradiance on the collector’s plane. It is shown that the new tracker system can be very efficient since its plane intercepts, at least, 98% of the insolation with respect to a two-axis tracker. The proposed system can be utilized in solar-related applications (photovoltaic or thermal).  相似文献   
159.
160.
Epitaxial lamellar gallium selenide (GaSe) semiconductors have been grown on trench-patterned silicon (Si) substrates by molecular beam epitaxy. An intriguing star-like patterned morphology was identified by atomic force microscopy on these epilayers. This non-trivial feature can be correlated with the accumulation of stacking faults of two concurrent epitaxial domains around self-oriented triangular pits developed earlier on the Si(111) surface by the chemical etching. Crystallographic considerations show how the stars can be formed.  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