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   470993篇
  免费   6770篇
  国内免费   1741篇
电工技术   8525篇
综合类   382篇
化学工业   68891篇
金属工艺   16492篇
机械仪表   13687篇
建筑科学   12037篇
矿业工程   1387篇
能源动力   13447篇
轻工业   45819篇
水利工程   4026篇
石油天然气   5005篇
武器工业   20篇
无线电   61922篇
一般工业技术   88983篇
冶金工业   90541篇
原子能技术   7875篇
自动化技术   40465篇
  2021年   3785篇
  2020年   2814篇
  2019年   3382篇
  2018年   5554篇
  2017年   5584篇
  2016年   5946篇
  2015年   4143篇
  2014年   7125篇
  2013年   21994篇
  2012年   12048篇
  2011年   16883篇
  2010年   13353篇
  2009年   15119篇
  2008年   15986篇
  2007年   15840篇
  2006年   14331篇
  2005年   12849篇
  2004年   12428篇
  2003年   12549篇
  2002年   11549篇
  2001年   12337篇
  2000年   11283篇
  1999年   12215篇
  1998年   30883篇
  1997年   21394篇
  1996年   16218篇
  1995年   12269篇
  1994年   10801篇
  1993年   10680篇
  1992年   7528篇
  1991年   7189篇
  1990年   6904篇
  1989年   6551篇
  1988年   6392篇
  1987年   5271篇
  1986年   5132篇
  1985年   5985篇
  1984年   5377篇
  1983年   5112篇
  1982年   4685篇
  1981年   4686篇
  1980年   4442篇
  1979年   4110篇
  1978年   3798篇
  1977年   4560篇
  1976年   6085篇
  1975年   3181篇
  1974年   3060篇
  1973年   3075篇
  1972年   2504篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
One specific class of non-linear evolution equations, known as the Tzitzéica-type equations, has received great attention from a group of researchers involved in non-linear science. In this article, new exact solutions of the Tzitzéica-type equations arising in non-linear optics, including the Tzitzéica, Dodd–Bullough–Mikhailov and Tzitzéica–Dodd–Bullough equations, are obtained using the expa function method. The integration technique actually suggests a useful and reliable method to extract new exact solutions of a wide range of non-linear evolution equations.  相似文献   
2.
Clean Technologies and Environmental Policy - Food production and consumption is one of the major causes of global environmental degradation. One way to address environmental impacts in the food...  相似文献   
3.
ABSTRACT

Bacteriocin is a proteinaceous biomolecule produced by bacteria (both Gram-positive and Gram-negative) that exhibits antimicrobial activity against closely related species, and food-borne pathogens. It has recently gained importance and attracted the attention of several researchers looking to produce it from various substrates and bacterial strains. This ushers in a new era of food preservation where the use of bacteriocin in food products will be an alternative to chemical preservatives, and heat treatment which are understood to cause unwanted side effects, and reduce sensory and nutritional quality. However, this new market depends on the success of novel downstream separation schemes from various types of crude feedstocks which are both effective and economic. This review focuses on the downstream separation of bacteriocin from various sources using both conventional and novel techniques. Finally, recommendations for future interesting areas of research that need to be pursued are highlighted.  相似文献   
4.
5.
6.
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   
7.
8.
Wu  Li  Li  Jing  Fu  Caixia  Kühn  Bernd  Wang  Xiaolin 《Magma (New York, N.Y.)》2019,32(4):501-509
Magnetic Resonance Materials in Physics, Biology and Medicine - To investigate the value of using diffusion-weighted imaging (DWI) and intravoxel incoherent motion DWI (IVIM-DWI) to assess the...  相似文献   
9.
We explore the possibility of characterizing sperm cells without the need to stain them using spectral and fluorescence lifetime analyses after multi-photon excitation in an insect model. The autofluorescence emission spectrum of sperm of the common bedbug, Cimex lectularius, was consistent with the presence of flavins and NAD(P)H. The mean fluorescence lifetimes showed smaller variation in sperm extracted from the male (tau m, τm = 1.54–1.84 ns) than in that extracted from the female sperm storage organ (tau m, τm = 1.26–2.00 ns). The fluorescence lifetime histograms revealed four peaks. These peaks (0.18, 0.92, 2.50 and 3.80 ns) suggest the presence of NAD(P)H and flavins and show that sperm metabolism can be characterized using fluorescence lifetime imaging. The difference in fluorescence lifetime variation between the sexes is consistent with the notion that female animals alter the metabolism of sperm cells during storage. It is not consistent, however, with the idea that sperm metabolism represents a sexually selected character that provides females with information about the male genotype.  相似文献   
10.
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