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   570891篇
  免费   6040篇
  国内免费   1621篇
化学   275660篇
晶体学   7981篇
力学   29281篇
综合类   14篇
数学   96446篇
物理学   169170篇
  2021年   3936篇
  2020年   4301篇
  2019年   4653篇
  2018年   20328篇
  2017年   20577篇
  2016年   16671篇
  2015年   7011篇
  2014年   9043篇
  2013年   20836篇
  2012年   21828篇
  2011年   36244篇
  2010年   23336篇
  2009年   23599篇
  2008年   30730篇
  2007年   34665篇
  2006年   16825篇
  2005年   20929篇
  2004年   17472篇
  2003年   16251篇
  2002年   13747篇
  2001年   13815篇
  2000年   10621篇
  1999年   8102篇
  1998年   6790篇
  1997年   6472篇
  1996年   6393篇
  1995年   5683篇
  1994年   5560篇
  1993年   5378篇
  1992年   5967篇
  1991年   6068篇
  1990年   5779篇
  1989年   5604篇
  1988年   5635篇
  1987年   5515篇
  1986年   5224篇
  1985年   6705篇
  1984年   6843篇
  1983年   5435篇
  1982年   5520篇
  1981年   5488篇
  1980年   5101篇
  1979年   5481篇
  1978年   5628篇
  1977年   5437篇
  1976年   5411篇
  1975年   4986篇
  1974年   4949篇
  1973年   4980篇
  1972年   3492篇
排序方式: 共有10000条查询结果,搜索用时 984 毫秒
131.
In order to investigate the characteristics of force chains in a granular flow system, a parallel plate shear cell is constructed to simulate the shear movement of an infinite parallel plate and observe variations in relevant parameters. The shear dilatancy process is divided into three stages, namely, plastic strain, macroscopic failure, and granular recombination. The stickslip phenomenon is highly connected with the evolution of force chains during the shear dilatancy process. The load–distribution rate curves and patterns of the force chains are utilized to describe the load-carrying behaviors and morphologic changes of force chains separately. Force chains, namely, “diagonal gridding,” “tadpole-shaped,” and “pinnate” are defined according to the form of the force chains in the corresponding three stages.  相似文献   
132.
133.
134.
135.
136.
137.
138.
In the last decade, catalytic chemical vapor deposition (CVD) has been intensively explored for the growth of single-layer graphene (SLG). Despite the scattering of guidelines and procedures, variables such as the surface texture/chemistry of catalyst metal foils, carbon feedstock, and growth process parameters have been well-scrutinized. Still, questions remain on how best to standardize the growth procedure. The possible correlation of procedures between different CVD setups is an example. Here, two thermal CVD reactors were explored to grow graphene on Cu foil. The design of these setups was entirely distinct, one being a “showerhead” cold-wall type, whereas the other represented the popular “tubular” hot-wall type. Upon standardizing the Cu foil surface, it was possible to develop a procedure for cm2-scale SLG growth that differed only by the carrier gas flow rate used in the two reactors.  相似文献   
139.
Journal of Solid State Electrochemistry - In this work, the use of neodymium electrodes as a basis for the immobilization of magnetite nanoparticles has been carried out. The sensitivity and...  相似文献   
140.
The influenza virus is a global threat to human health causing unpredictable yet recurring pandemics, the last four emerging over the course of a hundred years. As our knowledge of influenza virus evolution, distribution, and transmission has increased, paths to pandemic preparedness have become apparent. In the 1950s, the World Health Organization (WHO) established a global influenza surveillance network that is now composed of institutions in 122 member states. This and other surveillance networks monitor circulating influenza strains in humans and animal reservoirs and are primed to detect influenza strains with pandemic potential. Both the United States Centers for Disease Control and Prevention and the WHO have also developed pandemic risk assessment tools that evaluate specific aspects of emerging influenza strains to develop a systematic process of determining research and funding priorities according to the risk of emergence and potential impact. Here, we review the history of influenza pandemic preparedness and the current state of preparedness, and we propose additional measures for improvement. We also comment on the intersection between the influenza pandemic preparedness network and the current SARS-CoV-2 crisis. We must continually evaluate and revise our risk assessment and pandemic preparedness plans and incorporate new information gathered from research and global crises.Subject terms: Influenza virus, Infectious diseases  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