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   437926篇
  免费   21075篇
  国内免费   11469篇
化学   234075篇
晶体学   6029篇
力学   23343篇
综合类   595篇
数学   62433篇
物理学   143995篇
  2022年   4884篇
  2021年   5570篇
  2020年   6154篇
  2019年   6226篇
  2018年   14449篇
  2017年   15041篇
  2016年   12995篇
  2015年   8360篇
  2014年   10043篇
  2013年   17772篇
  2012年   21621篇
  2011年   31202篇
  2010年   20147篇
  2009年   19820篇
  2008年   25713篇
  2007年   28408篇
  2006年   14673篇
  2005年   18899篇
  2004年   13984篇
  2003年   12434篇
  2002年   10252篇
  2001年   9563篇
  2000年   7664篇
  1999年   6255篇
  1998年   5306篇
  1997年   5119篇
  1996年   5416篇
  1995年   4552篇
  1994年   4565篇
  1993年   4110篇
  1992年   4297篇
  1991年   4274篇
  1990年   3895篇
  1989年   3569篇
  1988年   3470篇
  1987年   3295篇
  1986年   3266篇
  1985年   4050篇
  1984年   4096篇
  1983年   3316篇
  1982年   3581篇
  1981年   3313篇
  1980年   3024篇
  1979年   3261篇
  1978年   3453篇
  1977年   3432篇
  1976年   3488篇
  1975年   3156篇
  1974年   3267篇
  1973年   3350篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Kinetics and Catalysis - The catalytic properties of a nickel phosphide catalyst supported on silica gel in the reductive amination of carbonyl compounds were studied in a flow reactor using...  相似文献   
2.
In this study, the transverse relaxation time (T2) of activated carbon (AC) in different relative environment humidity was detected firstly by low-field nuclear magnetic resonance (LFNMR). The pore size (diameter) of AC distributions was calculated by the relationship between T2 and surface relaxation rate (ρ), where ρ was obtained by the detection of nine porous materials with known pore size. The results showed that the pore size distributions of AC calculated by ρ < 0.19 nm/ms were in good agreement with that obtained by nitrogen adsorption method and proved that LFNMR as a new detection method was feasible for characterizing AC pore size distribution.  相似文献   
3.
Two series of novel alternating copolyoxamides (PAnT-alt-n2 and PAn2-alt-62) are synthesized via solution/solid-state polycondensation (SSP). The alternating structures are analyzed carefully with 1H NMR and 13C NMR spectra. The melting behaviors, thermal stabilities, crystal structures and crystallinities are systematically evaluated by DSC, TGA and WAXD. The results reveal that these alternating copolyoxamides possess almost perfect alternating chain structures and have high melting temperature (Tm > 270 °C), high crystallinity (Xc > 32%) and high decomposition temperature (T5 > 405 °C) as well as low saturated water absorption (<3.5 wt%), which suggests that they have high potential as engineering plastic of high heat resistant.  相似文献   
4.
Yang  T. L.  Kao  C. L.  Kuo  C. E.  Yeh  H. C.  Li  W. J.  Li  H. T.  Chen  C. Y. 《Chemistry of Natural Compounds》2022,58(5):825-827
Chemistry of Natural Compounds - A novel bibenzyl derivative, hydrangchinenin (1), was isolated from the stems of Hydrangea chinensis Maxim. (Hydrangeaceae). Its structure was determined on the...  相似文献   
5.
Kinetics and Catalysis - A new ruthenium(II) cage complex with polar terminal groups in the apical substituents has been synthesized; the molecular design of the complex contributes to the...  相似文献   
6.
The coordination chemistry of f-block elements (lanthanide and actinide) in molten salts has become a resounding topic in view of its great importance to the research and development (R&D) of molten salt reactors and pyroprocessing. In this Review article, a general overview of the coordination chemistry of f-block elements in molten salts is provided including past achievements and recent advances. Particular emphases are placed on the oxidation state, speciation, and solution structure of f-block metal ions in molten salts, as well as their relationships with the salt composition. Furthermore, this review briefly discusses the spectroscopic and theoretical methods that complement each other in revealing the coordination properties.  相似文献   
7.
Fan  K.  Lu  R. S.  Liang  K. K.  Hou  Z. C. 《High Energy Chemistry》2022,56(4):264-269
High Energy Chemistry - Modification of Polyvinylidene fluoride (PVDF) by radiation grafting is a research hotspot in recent years. In this study, the monomer 2-Hydroxyethyl methacrylate (HEMA) was...  相似文献   
8.
9.
10.
Russian Journal of General Chemistry - The review article traces the main trends of the synthetic approach to the solution of the problem of overcoming the resistance of pathogenic bacterial...  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