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   515680篇
  免费   5420篇
  国内免费   1434篇
化学   264088篇
晶体学   7551篇
力学   23750篇
综合类   10篇
数学   70256篇
物理学   156879篇
  2020年   2999篇
  2019年   3044篇
  2018年   11581篇
  2017年   12362篇
  2016年   9681篇
  2015年   5329篇
  2014年   6487篇
  2013年   18926篇
  2012年   18287篇
  2011年   28872篇
  2010年   18088篇
  2009年   18004篇
  2008年   25905篇
  2007年   29034篇
  2006年   16306篇
  2005年   21133篇
  2004年   16506篇
  2003年   14932篇
  2002年   12932篇
  2001年   14136篇
  2000年   10834篇
  1999年   8402篇
  1998年   6465篇
  1997年   6387篇
  1996年   6465篇
  1995年   5882篇
  1994年   5611篇
  1993年   5341篇
  1992年   6198篇
  1991年   6138篇
  1990年   5792篇
  1989年   5575篇
  1988年   5811篇
  1987年   5529篇
  1986年   5220篇
  1985年   7254篇
  1984年   7360篇
  1983年   5988篇
  1982年   6325篇
  1981年   6225篇
  1980年   5975篇
  1979年   6376篇
  1978年   6460篇
  1977年   6345篇
  1976年   6260篇
  1975年   6051篇
  1974年   5897篇
  1973年   6110篇
  1972年   3663篇
  1971年   2753篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
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   
92.
93.
94.
95.
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   
96.
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   
97.
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   
98.
High-energy assisted extraction techniques, like ultrasound assisted extraction (UAE) and microwave assisted extraction (MAE), are widely applied over the last years for the recovery of bioactive compounds such as carotenoids, antioxidants and phenols from foods, animals and herbal natural sources. Especially for the case of xanthophylls, the main carotenoid group of crustaceans, they can be extracted in a rapid and quantitative way with the use of UAE and MAE.  相似文献   
99.
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   
100.
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