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   25449篇
  免费   4114篇
  国内免费   3057篇
化学   18172篇
晶体学   288篇
力学   1481篇
综合类   279篇
数学   3003篇
物理学   9397篇
  2024年   14篇
  2023年   513篇
  2022年   521篇
  2021年   724篇
  2020年   1032篇
  2019年   978篇
  2018年   793篇
  2017年   784篇
  2016年   1163篇
  2015年   1076篇
  2014年   1339篇
  2013年   1790篇
  2012年   2202篇
  2011年   2233篇
  2010年   1557篇
  2009年   1489篇
  2008年   1684篇
  2007年   1538篇
  2006年   1458篇
  2005年   1208篇
  2004年   988篇
  2003年   857篇
  2002年   756篇
  2001年   651篇
  2000年   559篇
  1999年   620篇
  1998年   511篇
  1997年   442篇
  1996年   449篇
  1995年   420篇
  1994年   373篇
  1993年   344篇
  1992年   302篇
  1991年   252篇
  1990年   249篇
  1989年   176篇
  1988年   139篇
  1987年   87篇
  1986年   109篇
  1985年   72篇
  1984年   43篇
  1983年   42篇
  1982年   41篇
  1981年   21篇
  1980年   9篇
  1979年   6篇
  1976年   1篇
  1957年   5篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
61.
62.
63.
Wu  ChunHui  Zhu  Ji-Hua  Chen  Na  Liu  JingBing  Wang  Hao 《Ionics》2015,21(8):2303-2307
Ionics - A novel stereoscopic snowflake-like CoO material is synthesized via a simple two-step process, including the hydrothermal process for the formation of the stereoscopic snowflake-like...  相似文献   
64.
Well‐defined tertiary amine‐based pH‐responsive homopolymers and block copolymers were synthesized via reversible addition‐fragmentation chain transfer (RAFT) polymerization using 4‐cyanopentanoic acid dithiobenzoate (CPAD) as the RAFT agent for homopolymers and a poly(ethylene glycol) (PEG) macro‐RAFT agent for the block copolymers. 1H NMR and gel permeation chromatography results confirmed the successful synthesis of these homopolymers and block copolymers. Kinetics studies indicated that the formation of both the homopolymers and the block copolymers were well defined. The pKa titration experiments suggested that the homopolymers and the related block copolymers have a similar pKa. The dynamic light scattering investigation showed that all of the block copolymers underwent a sharp transition from unimers to micelles around their pKa and the hydrodynamic diameter (Dh) was not only dependent on the molecular weight but also on the composition of the block copolymers. The polymer solution of PEG‐b‐PPPDEMA formed the largest micelle compare to the PEG‐b‐PDPAEMA and PEG‐b‐PDBAEMA with a similar molecular weight. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1010–1022  相似文献   
65.
66.
A heterometallic cluster [Ag6Au6(ethisterone)12] of an unprecedented topology was synthesized and characterized. A sensitive and specific probe for estrogen receptor α (ERα) has been developed for the first time based on the enhancement of the Ag6Au6 luminescence.  相似文献   
67.
68.
A rhodium(III)‐catalyzed cross‐coupling of benzyl thioethers and aryl carboxylic acids through the two directing groups is reported. Useful structures with diverse substituents were efficiently synthesized in one step with the cleavage of four bonds (C H, C S, O H) and the formation of two bonds (C C, C O). The formed structure is the privileged core in natural products and bioactive molecules. This work highlights the power of using two different directing groups to enhance the selectivity of a double C H activation, the first of such examples in cross‐oxidative coupling.  相似文献   
69.
70.
This study was aimed at addressing the present challenge of cascade reactions, namely, how to furnish the catalysts with desired and hierarchical catalytic ability. This issue was addressed by constructing a cascade‐reaction nanoreactor made of a bifunctional molecularly imprinted polymer containing acidic catalytic sites and Pt nanoparticles. The acidic catalytic sites within the imprinted polymer allowed one specified reaction, whereas the encapsulated Pt nanoparticles were responsible for another coupled reaction. To that end, the unique imprinted polymer was fabricated by using two well‐coupled templates, that is, 4‐nitrophenyl acetate and 4‐nitrophenol. The catalytic hydrolysis of the former compound at the acidic catalytic sites led to the formation of the latter compound, which was further reduced by the encapsulated Pt nanoparticles to 4‐aminophenol. Therefore, this nanoreactor demonstrated a catalytic‐cascade ability. This protocol opens up the opportunity to develop functional catalysts for complicated chemical processes.  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