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   1402788篇
  免费   30421篇
  国内免费   9133篇
化学   712619篇
晶体学   20576篇
力学   76153篇
综合类   114篇
数学   248295篇
物理学   384585篇
  2021年   13863篇
  2020年   16233篇
  2019年   16435篇
  2018年   14511篇
  2017年   12735篇
  2016年   29313篇
  2015年   21454篇
  2014年   31132篇
  2013年   75951篇
  2012年   42251篇
  2011年   41700篇
  2010年   39636篇
  2009年   41543篇
  2008年   39576篇
  2007年   35656篇
  2006年   40049篇
  2005年   33000篇
  2004年   33777篇
  2003年   31050篇
  2002年   31711篇
  2001年   31164篇
  2000年   26471篇
  1999年   23369篇
  1998年   21459篇
  1997年   21314篇
  1996年   21425篇
  1995年   19399篇
  1994年   18858篇
  1993年   18519篇
  1992年   18725篇
  1991年   18865篇
  1990年   18062篇
  1989年   18092篇
  1988年   17697篇
  1987年   17616篇
  1986年   16575篇
  1985年   22976篇
  1984年   24065篇
  1983年   20150篇
  1982年   21790篇
  1981年   21014篇
  1980年   20351篇
  1979年   20650篇
  1978年   21863篇
  1977年   21468篇
  1976年   21185篇
  1975年   19869篇
  1974年   19524篇
  1973年   19935篇
  1972年   14441篇
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
861.
A series of donor-acceptor copolymers with dicyclopenta[cd,jk]pyrene and dicyclopenta[cd,lm]perylene acceptor units was prepared via palladium catalyzed cyclopenta-annulation reactions. The acceptor units were paired with diethynyl containing donor groups based on benzo[1,2-b:4,5-b’]dithiophene, thieno[3,2-b]thiophene, and 4-octyl-4H-dithieno[3,2-b:2′,3′-d]pyrrole to create six polymer variants. The cyclopentannulation polymerization resulted in copolymers with molecular weights (Mn) of 6–14 kDa and broad light absorption in the visible region with band gaps of 1.38–1.85 eV. The synthetic methodology, as well as optoelectronic properties, including thin-film absorption and cyclic voltammetry, of the donor-acceptor copolymers are presented.  相似文献   
862.
Bryostatins are a class of naturally occurring macrocyclic lactones with a unique fast developing portfolio of clinical applications, including treatment of AIDS, Alzheimer's disease, and cancer. This comprehensive account summarizes the recent progress (2014–present) in the development of bryostatins, including their total synthesis and biomedical applications. An emphasis is placed on the discussion of bryostatin 1 , the most-studied analogue to date. This review highlights the synthetic and biological challenges of bryostatins and provides an outlook on their future development.  相似文献   
863.
Monatshefte für Chemie - Chemical Monthly - A comparative analysis is performed on the stability constants $${\upbeta }_{1yn}$$ and intramolecular redox decomposition rate constants $$k_{n\; =...  相似文献   
864.
865.
Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques - A method for studying the magnetic dynamics of endofullerenes M@C2n (2n = 60, 70, …) and their derivatives,...  相似文献   
866.
Analytical and Bioanalytical Chemistry - Formaldehyde is often applied in the industrial production of different products, such as textiles, insulation materials, or cosmetics, due to its...  相似文献   
867.
Tunneled metal oxides such as α-Mn8O16 (hollandite) have proven to be compelling candidates for charge-storage materials in high-density batteries. In particular, the tunnels can support one-dimensional chains of K+ ions (which act as structure-stabilizing dopants) and H2O molecules, as these chains are favored by strong H-bonds and electrostatic interactions. In this work, we examine the role of water molecules in enhancing the stability of K+-doped α-Mn8O16 (cryptomelane). The combined experimental and theoretical analyses show that for high enough concentrations of water and tunnel-ions, H2O displaces K+ ions from their natural binding sites. This displacement becomes energetically favorable due to the formation of K2+ dimers, thereby modifying the stoichiometric charge of the system. These findings have potentially significant technological implications for the consideration of cryptomelane as a Li+/Na+ battery electrode. Our work establishes the functional role of water in altering the energetics and structural properties of cryptomelane, an observation that has frequently been overlooked in previous studies.

Water displaces potassium ions and initiates the formation of a homonuclear dimer ion (K2+) in the tunnels of hollandite.  相似文献   
868.
869.
870.
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