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   439905篇
  免费   4646篇
  国内免费   1488篇
化学   225819篇
晶体学   7118篇
力学   21391篇
综合类   25篇
数学   67001篇
物理学   124685篇
  2019年   2992篇
  2018年   13314篇
  2017年   13201篇
  2016年   11346篇
  2015年   4529篇
  2014年   6023篇
  2013年   16205篇
  2012年   14703篇
  2011年   23634篇
  2010年   14806篇
  2009年   15065篇
  2008年   18502篇
  2007年   20532篇
  2006年   11945篇
  2005年   11851篇
  2004年   11095篇
  2003年   10592篇
  2002年   9392篇
  2001年   10713篇
  2000年   8315篇
  1999年   6423篇
  1998年   5204篇
  1997年   5106篇
  1996年   5040篇
  1995年   4650篇
  1994年   4444篇
  1993年   4208篇
  1992年   5151篇
  1991年   4963篇
  1990年   4827篇
  1989年   4855篇
  1988年   4831篇
  1987年   4872篇
  1986年   4594篇
  1985年   6032篇
  1984年   6056篇
  1983年   4897篇
  1982年   5188篇
  1981年   5215篇
  1980年   4917篇
  1979年   5314篇
  1978年   5535篇
  1977年   5490篇
  1976年   5263篇
  1975年   4897篇
  1974年   4825篇
  1973年   4817篇
  1972年   3247篇
  1968年   3394篇
  1967年   3474篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
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   
82.
83.
84.
85.
Journal of Thermal Analysis and Calorimetry - Over the last few decades, tremendous consideration is drawn towards corrugation surfaces because of their advantages over the improvement in thermal...  相似文献   
86.
Oral microbes have the capacity to spread throughout the gastrointestinal system and are strongly associated with multiple diseases. Given that tonsils are located between the oral cavity and the laryngopharynx at the gateway of the alimentary and respiratory tracts, tonsillar tissue may also be affected by microbiota from both the oral cavity (saliva) and the alimentary tract. Here, we analyzed the distribution and association of the microbial communities in the saliva and tonsils of Korean children subjected to tonsillectomy because of tonsil hyperplasia (n = 29). The microbiome profiles of saliva and tonsils were established via 16S rRNA gene sequencing. Based on the alpha diversity indices, the microbial communities of the two groups showed high similarities. According to Spearman’s ranking correlation analysis, the distribution of Treponema, the causative bacterium of periodontitis, in saliva and tonsils was found to have a significant positive correlation. Two representative microbes, Prevotella in saliva and Alloprevotella in tonsils, were negatively correlated, while Treponema 2 showed a strong positive correlation between saliva and tonsils. Taken together, strong similarities in the microbial communities of the tonsils and saliva are evident in terms of diversity and composition. The saliva microbiome is expected to significantly affect the tonsil microbiome. Furthermore, we suggest that our study creates an opportunity for tonsillar microbiome research to facilitate the development of novel microbiome-based therapeutic strategies.Subject terms: Comparative genomics, Metagenomics  相似文献   
87.
ABSTRACT

The authors present the results of an investigation in Fe–Ni-Cr austenitic alloys of the low-temperature deformation-induced segregations of nickel that form in the micro regions being (i) located close to grain- and subgrain boundaries and (ii) characteristic of the concentration and magnetic inhomogeneities indicated by the appearance of a dark diffraction contrast at the electron diffraction patterns taken from these regions typical (at the same time) of an enhanced value of Curie temperature. The observed effects were connected with the micro distortions caused by the local change of lattice parameter because of an increase in nickel concentration, as well as in the result of a magnetostriction dilatation. Using methods of the X-ray energy dispersive spectroscopy (XEDS) and atomic-probe body-section radiography (tomography – APT) has made it possible to determine the borders of those regions of austenite that were characteristic of an enhanced concentration of nickel in the fields of the localisation of a deformation-induced segregation of nickel in the vicinity of grain (subgrain) boundaries of austenitic alloys of the types Fe–13Cr–30Ni and Fe–37Ni–3Ti.  相似文献   
88.
89.
90.
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