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   574070篇
  免费   7238篇
  国内免费   1445篇
电工技术   11464篇
综合类   944篇
化学工业   82356篇
金属工艺   23874篇
机械仪表   20237篇
建筑科学   13968篇
矿业工程   2498篇
能源动力   14169篇
轻工业   47831篇
水利工程   5628篇
石油天然气   8093篇
武器工业   75篇
无线电   71618篇
一般工业技术   113423篇
冶金工业   100202篇
原子能技术   10475篇
自动化技术   55898篇
  2021年   3909篇
  2019年   3802篇
  2018年   13168篇
  2017年   13637篇
  2016年   10550篇
  2015年   4937篇
  2014年   7784篇
  2013年   23467篇
  2012年   14719篇
  2011年   24249篇
  2010年   20272篇
  2009年   21225篇
  2008年   21983篇
  2007年   23506篇
  2006年   14833篇
  2005年   16546篇
  2004年   14743篇
  2003年   14147篇
  2002年   12910篇
  2001年   12525篇
  2000年   12081篇
  1999年   12453篇
  1998年   29074篇
  1997年   21044篇
  1996年   16643篇
  1995年   12967篇
  1994年   11645篇
  1993年   11301篇
  1992年   8752篇
  1991年   8295篇
  1990年   8088篇
  1989年   7649篇
  1988年   7439篇
  1987年   6285篇
  1986年   6281篇
  1985年   7439篇
  1984年   6818篇
  1983年   6285篇
  1982年   5740篇
  1981年   6001篇
  1980年   5556篇
  1979年   5407篇
  1978年   5142篇
  1977年   6087篇
  1976年   7738篇
  1975年   4605篇
  1974年   4441篇
  1973年   4483篇
  1972年   3660篇
  1971年   3306篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
61.
A layer-by-layer analysis of the structures, the phase compositions, and the defect substructures of differentially hardened rails has been carried by optical and transmission electron microscopy. It is found that the material volume of the rail head fillet is cooled faster than the volume located along the central axis.  相似文献   
62.
Copper particles were incorporated and retained in elemental state in an aluminium matrix by friction stir processing thereby producing a non-equilibrium particulate composite. The processed Al–Cup composite exhibited improved strength with significantly high ductility. The composite was stable up to a temperature of more than 300°C. Thermal exposure at 350°C for more than 10 min led to diffusion of Cu atoms into the Al matrix forming a core-shell type structure in the Cu particles and thus producing an Al–Cu core-shell composite. The shell consists of multiple layers, the thickness of which was controllable.  相似文献   
63.
64.
Metallurgical and Materials Transactions A - The influence of the chemical composition on the crystallization process, amorphous phase formation, and the anticorrosion properties of Al-Zr-Ni-Fe-Y...  相似文献   
65.
ABSTRACT

This paper deals with asymptotic stabilisation of a class of nonlinear input-delayed systems via dynamic output feedback in the presence of disturbances. The proposed strategy has the structure of an observer-based control law, in which the observer estimates and predicts both the plant state and the external disturbance. A nominal delay value is assumed to be known and stability conditions in terms of linear matrix inequalities are derived for fast-varying delay uncertainties. Asymptotic stability is achieved if the disturbance or the time delay is constant. The controller design problem is also addressed and a numerical example with an unstable system is provided to illustrate the usefulness of the proposed strategy.  相似文献   
66.
67.
68.
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   
69.
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   
70.
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   
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