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   575797篇
  免费   7239篇
  国内免费   1448篇
电工技术   11468篇
综合类   949篇
化学工业   83584篇
金属工艺   23867篇
机械仪表   20251篇
建筑科学   14036篇
矿业工程   2499篇
能源动力   14171篇
轻工业   48268篇
水利工程   5624篇
石油天然气   8096篇
武器工业   75篇
无线电   71607篇
一般工业技术   113429篇
冶金工业   100198篇
原子能技术   10472篇
自动化技术   55890篇
  2021年   3929篇
  2019年   3801篇
  2018年   13168篇
  2017年   13636篇
  2016年   10549篇
  2015年   4937篇
  2014年   7782篇
  2013年   23464篇
  2012年   14719篇
  2011年   24249篇
  2010年   20269篇
  2009年   21223篇
  2008年   21980篇
  2007年   23504篇
  2006年   14825篇
  2005年   16542篇
  2004年   14741篇
  2003年   14142篇
  2002年   12907篇
  2001年   12521篇
  2000年   12076篇
  1999年   12451篇
  1998年   29073篇
  1997年   21044篇
  1996年   16639篇
  1995年   12964篇
  1994年   11645篇
  1993年   11301篇
  1992年   8749篇
  1991年   8292篇
  1990年   8082篇
  1989年   7649篇
  1988年   7438篇
  1987年   6373篇
  1986年   6364篇
  1985年   7532篇
  1984年   6914篇
  1983年   6391篇
  1982年   5835篇
  1981年   6097篇
  1980年   5633篇
  1979年   5483篇
  1978年   5212篇
  1977年   6157篇
  1976年   7812篇
  1975年   4666篇
  1974年   4489篇
  1973年   4545篇
  1972年   3685篇
  1971年   3365篇
排序方式: 共有10000条查询结果,搜索用时 234 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.
63.
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   
64.
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   
65.
66.
67.
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   
68.
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   
69.
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   
70.
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