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   26413篇
  免费   4310篇
  国内免费   2714篇
化学   18830篇
晶体学   332篇
力学   1583篇
综合类   132篇
数学   3040篇
物理学   9520篇
  2024年   15篇
  2023年   540篇
  2022年   631篇
  2021年   871篇
  2020年   1128篇
  2019年   1110篇
  2018年   905篇
  2017年   821篇
  2016年   1285篇
  2015年   1247篇
  2014年   1419篇
  2013年   1910篇
  2012年   2500篇
  2011年   2574篇
  2010年   1697篇
  2009年   1610篇
  2008年   1752篇
  2007年   1586篇
  2006年   1427篇
  2005年   1192篇
  2004年   876篇
  2003年   684篇
  2002年   642篇
  2001年   477篇
  2000年   461篇
  1999年   527篇
  1998年   440篇
  1997年   436篇
  1996年   446篇
  1995年   354篇
  1994年   303篇
  1993年   233篇
  1992年   234篇
  1991年   201篇
  1990年   170篇
  1989年   142篇
  1988年   95篇
  1987年   109篇
  1986年   88篇
  1985年   82篇
  1984年   47篇
  1983年   43篇
  1982年   35篇
  1981年   18篇
  1980年   11篇
  1979年   9篇
  1978年   6篇
  1976年   9篇
  1975年   11篇
  1936年   5篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
981.
982.
983.
984.
985.
986.
A green and cost‐effective process for the convenient synthesis of acylphloroglucinol 3‐C‐glucosides from 2‐O‐glucosides was exploited using a novel C‐glycosyltransferase (MiCGTb) from Mangifera indica. Compared with previously characterized CGTs, MiCGTb exhibited unique de‐O‐glucosylation promiscuity and high regioselectivity toward structurally diverse 2‐O‐glucosides of acylphloroglucinol and achieved high yields of C‐glucosides even with a catalytic amount of uridine 5′‐diphosphate (UDP). These findings demonstrate for the first time the significant potential of a single‐enzyme approach to the synthesis of bioactive C‐glucosides from both natural and unnatural acylphloroglucinol 2‐O‐glucosides.  相似文献   
987.
This paper studies the factors that affect people coming to China. We select the spending of United States and South Korea, GDP, railway transportation capacity of China as observations. Based on the data from 1988 to 2015, we use the ordinary least squares analysis regression model and present a most reasonable regression equation. It is found that South Korea’s spending is negative to the number of visitors, whereas the spending of US is positive. On comparing the effect of other variables, the growth of railway transportation capacity and the overseas travel expenses of South Korea or United States, have almost no significant impact on the number of people coming to China. However, as China economic growth increasing rapidly, more and more people are willing to come.  相似文献   
988.
Zhou  Jiahui  Jiang  Feng  Li  Sijie  Xu  Zhijie  Sun  Wei  Ji  Xiaobo  Yang  Yue 《Journal of Solid State Electrochemistry》2019,23(7):1991-2000
Journal of Solid State Electrochemistry - Considering serious pollution from the traditional chemical synthesis process, the resource-rich, clean electrode materials are greatly desired....  相似文献   
989.

Research about two-dimensional (2D) materials is growing exponentially across various scientific and engineering disciplines due to the wealth of unusual physical phenomena that occur when charge transport is confined to a plane. The applications of 2D materials are highly affected by the electrical properties of these materials, including current distribution, surface potential, dielectric response, conductivity, permittivity, and piezoelectric response. Hence, it is very crucial to characterize these properties at the nanoscale. The Atomic Force Microscopy (AFM)-based techniques are powerful tools that can simultaneously characterize morphology and electrical properties of 2D materials with high spatial resolution, thus being more and more extensively used in this research field. Here, the principles of these AFM techniques are reviewed in detail. After that, their representative applications are further demonstrated in the local characterization of various 2D materials’ electrical properties.

  相似文献   
990.
High pressure can effectively control the phase transition of MoTe2 in experiment, but the mechanism is still unclear. In this work, we show by first-principles calculations that the phase transition is suppressed and 1T phase becomes more stable under high pressure, which originates from the pressure-induced change of the interlayer band occupancies near the Fermi energy. Specifically, the interlayer states of 1T phase tend to be fully occupied under high pressure, while they keep partially occupied for the Td phase. The increase of the band occupancies makes the 1T phase more favorable in energy and prevents the structure changing from 1T to Td phase. Moreover, we also analyze the superconductivity under high pressure based on BCS theory by calculating the density of states and phonon spectra. Our results may shed some light on understanding the relationship between the interlayer band occupancy and crystal stability of MoTe2 under high pressures.  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