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   506798篇
  免费   5854篇
  国内免费   1598篇
化学   255193篇
晶体学   7175篇
力学   25073篇
综合类   13篇
数学   79950篇
物理学   146846篇
  2021年   3763篇
  2020年   4189篇
  2019年   4523篇
  2018年   15595篇
  2017年   15324篇
  2016年   14496篇
  2015年   6321篇
  2014年   8788篇
  2013年   20416篇
  2012年   19034篇
  2011年   28850篇
  2010年   18659篇
  2009年   18917篇
  2008年   23693篇
  2007年   25473篇
  2006年   16415篇
  2005年   15707篇
  2004年   14903篇
  2003年   13714篇
  2002年   12633篇
  2001年   13625篇
  2000年   10323篇
  1999年   8031篇
  1998年   6721篇
  1997年   6432篇
  1996年   6260篇
  1995年   5579篇
  1994年   5462篇
  1993年   5283篇
  1992年   5879篇
  1991年   5983篇
  1990年   5711篇
  1989年   5524篇
  1988年   5546篇
  1987年   5431篇
  1986年   5143篇
  1985年   6604篇
  1984年   6734篇
  1983年   5335篇
  1982年   5425篇
  1981年   5404篇
  1980年   5000篇
  1979年   5389篇
  1978年   5525篇
  1977年   5403篇
  1976年   5344篇
  1975年   4928篇
  1974年   4896篇
  1973年   4904篇
  1972年   3472篇
排序方式: 共有10000条查询结果,搜索用时 24 毫秒
101.
102.
103.
104.
105.
106.
107.
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   
108.
ABSTRACT

By applying the geometric models and the theoretical equation, the surface tension, the molar volume and the density were studied. The empirical calculations were carried out in temperature range 623?K?≤?T?≤?1123?K. Only few thermophysical properties were estimated for eight quinary alloys: Sn3.55Ag0.5Cu3Bi3Sb, Sn3.48Ag0.5Cu3Bi5Sb, Sn3.48 Ag0.5Cu5Bi3Sb, Sn3.40 Ag0.5Cu5Bi5Sb, Sn3.53Ag1Cu3Bi3Sb, Sn3.46Ag1Cu3Bi5Sb, Sn3.46Ag1Cu5Bi3Sb, Sn3.38Ag1Cu5Bi5Sb. The results show that surface tension and density have a linear appearance for all temperatures. We have also studied the influence of the composition and temperature in the studied alloys. The obtained theoretical results are compared with the experimental ones and with the conventional Pb–Sn welds.  相似文献   
109.
Molecular dynamics simulation was performed to study the formation of cluster structure, interfaces, and surfaces with different curvature radii in a perfect nanocrystal passed through by a nonlinear wave. It is shown that this process is a type of nanostructure self-organization in response to an external energy flux with subsequent development of a strong rotational field.  相似文献   
110.
Journal of Solid State Electrochemistry - Due to their distinctive chemical, electronic, and environmental properties, polypyrrole is used as a blocking barrier for methanol leakage in direct...  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