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   179644篇
  免费   18962篇
  国内免费   24795篇
化学   114317篇
晶体学   3703篇
力学   10794篇
综合类   2313篇
数学   23619篇
物理学   68655篇
  2023年   1664篇
  2022年   4308篇
  2021年   4561篇
  2020年   4981篇
  2019年   5223篇
  2018年   5323篇
  2017年   6016篇
  2016年   6510篇
  2015年   6114篇
  2014年   8063篇
  2013年   11075篇
  2012年   11334篇
  2011年   12136篇
  2010年   10332篇
  2009年   10375篇
  2008年   11339篇
  2007年   10647篇
  2006年   9656篇
  2005年   8477篇
  2004年   7096篇
  2003年   5751篇
  2002年   5862篇
  2001年   5417篇
  2000年   4936篇
  1999年   3452篇
  1998年   2685篇
  1997年   2238篇
  1996年   2184篇
  1995年   1945篇
  1994年   2002篇
  1993年   1866篇
  1992年   1765篇
  1991年   1682篇
  1990年   1700篇
  1989年   1575篇
  1988年   1302篇
  1987年   1292篇
  1986年   1191篇
  1985年   1295篇
  1984年   1308篇
  1983年   1092篇
  1982年   1066篇
  1981年   948篇
  1979年   1028篇
  1978年   957篇
  1977年   994篇
  1976年   1085篇
  1975年   942篇
  1974年   968篇
  1973年   969篇
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
41.
42.
An organocatalytic asymmetric chlorinative dearomatization of naphthols was realized for the first time, providing chiral naphthalenones with a Cl-containing all-substituted stereocenter in excellent yields and enantioselectivity (up to 97% yield and 96% ee). The reaction features mild reaction conditions, good tolerance of diverse functional groups and simple reaction operation.  相似文献   
43.
Theoretical and Computational Fluid Dynamics - The present study aims to simulate a collision of two droplets containing immiscible liquids by employing a three- dimensional incompressible smoothed...  相似文献   
44.
45.
46.
Hierarchically porous metal–organic frameworks (HP-MOFs) are promising in various applications. Most reported HP-MOFs are prepared based on the generation of mesopores in microporous frameworks, and the formed mesopores are connected by microporous channels, limiting the accessibility of mesopores for bulky molecules. A hierarchical structure is formed by constructing microporous MOFs in uninterrupted mesoporous tunnels. Using the confined space in as-prepared mesoporous silica, highly dispersed metal precursors for MOFs are coated on the internal surface of mesoporous tunnels. Ligand vapor-induced crystallization is employed to enable quantitative formation of MOFs in situ, in which sublimated ligands diffuse into mesoporous tunnels and react with metal precursors. The obtained hierarchically porous composites exhibit record-high adsorption capacity for the bulky molecule trypsin. The thermal and storage stability of trypsin is improved upon immobilization on the composites.  相似文献   
47.
Russian Journal of General Chemistry - 8-Phenyltetrazolo[5,1-b][1,3,4]thiadiazepine was obtained as a result of intermolecular cyclization of 1-amino-1H-tetrazole-5-thiol and 3-phenyl-2-propynal....  相似文献   
48.
A class of acceptor–donor–acceptor chromophoric small-molecule non-fullerene acceptors, 1–4, with difluoroboron(iii) β-diketonate (BF2bdk) as the electron-accepting moiety has been developed. Through the variation of the central donor unit and the modification on the peripheral substituents of the terminal BF2bdk acceptor unit, their photophysical and electrochemical properties have been systematically studied. Taking advantage of their low-lying lowest unoccupied molecular orbital energy levels (from −3.65 to −3.72 eV) and relatively high electron mobility (7.49 × 10−4 cm2 V−1 s−1), these BF2bdk-based compounds have been employed as non-fullerene acceptors in organic solar cells with maximum power conversion efficiencies of up to 4.31%. Moreover, bistable resistive memory characteristics with charge-trapping mechanisms have been demonstrated in these BF2bdk-based compounds. This work not only demonstrates for the first time the use of a boron(iii) β-diketonate unit in constructing non-fullerene acceptors, but also provides more insights into designing organic materials with multi-functional properties.

Boron(iii) β-diketonates have been demonstrated to serve as multi-functional materials in NFA-based OPVs and organic resistive memories.  相似文献   
49.
The results of investigation of optical image detectors designed for the largest problem, near-VUV, range of the spectrum are presented. The possibility of using a dual-stage image detection system to appreciably lower the sensitivity threshold and make computer data processing feasible is considered. The integration of a UV module into a wideband image detector is studied.  相似文献   
50.
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