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   1575287篇
  免费   32412篇
  国内免费   8356篇
化学   689573篇
晶体学   20781篇
力学   75940篇
综合类   111篇
数学   245336篇
物理学   385021篇
无线电   199293篇
  2021年   14837篇
  2020年   17444篇
  2019年   17572篇
  2018年   16423篇
  2017年   14850篇
  2016年   31071篇
  2015年   22158篇
  2014年   32964篇
  2013年   78936篇
  2012年   42648篇
  2011年   42061篇
  2010年   42323篇
  2009年   46897篇
  2008年   44303篇
  2007年   42324篇
  2006年   45472篇
  2005年   39602篇
  2004年   39765篇
  2003年   36864篇
  2002年   37309篇
  2001年   37306篇
  2000年   32502篇
  1999年   29395篇
  1998年   27673篇
  1997年   27536篇
  1996年   26991篇
  1995年   24754篇
  1994年   24261篇
  1993年   23612篇
  1992年   23599篇
  1991年   23735篇
  1990年   22570篇
  1989年   22193篇
  1988年   21362篇
  1987年   20117篇
  1986年   18948篇
  1985年   25454篇
  1984年   26544篇
  1983年   22418篇
  1982年   23764篇
  1981年   22947篇
  1980年   22226篇
  1979年   22206篇
  1978年   23385篇
  1977年   22993篇
  1976年   22570篇
  1975年   21223篇
  1974年   20871篇
  1973年   21359篇
  1972年   15490篇
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
911.
Radiophysics and Quantum Electronics - We consider whether it is possible in principle to retrieve the key parameters of the mixed layer in the upper ocean (its thickness, bulk eddy viscosity and...  相似文献   
912.
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   
913.
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   
914.
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   
915.
916.
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   
917.
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   
918.
919.
920.
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