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   465323篇
  免费   5562篇
  国内免费   1514篇
化学   245879篇
晶体学   6753篇
力学   20146篇
综合类   26篇
数学   59323篇
物理学   140272篇
  2021年   3971篇
  2020年   4317篇
  2019年   4667篇
  2018年   7095篇
  2017年   7207篇
  2016年   9736篇
  2015年   6250篇
  2014年   9142篇
  2013年   21106篇
  2012年   18610篇
  2011年   21594篇
  2010年   15059篇
  2009年   14728篇
  2008年   18453篇
  2007年   18378篇
  2006年   17013篇
  2005年   18770篇
  2004年   17189篇
  2003年   14110篇
  2002年   12247篇
  2001年   13661篇
  2000年   10248篇
  1999年   8064篇
  1998年   6686篇
  1997年   6392篇
  1996年   6163篇
  1995年   5539篇
  1994年   5453篇
  1993年   5251篇
  1992年   5979篇
  1991年   6057篇
  1990年   5776篇
  1989年   5563篇
  1988年   5573篇
  1987年   5431篇
  1986年   5138篇
  1985年   6607篇
  1984年   6735篇
  1983年   5335篇
  1982年   5416篇
  1981年   5394篇
  1980年   4988篇
  1979年   5381篇
  1978年   5523篇
  1977年   5406篇
  1976年   5392篇
  1975年   4958篇
  1974年   4926篇
  1973年   4919篇
  1972年   3494篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
32.
33.
A new amino‐functionalized strontium–carboxylate‐based metal–organic framework (MOF) has been synthesized that undergoes single crystal to single crystal (SC‐to‐SC) transformation upon desolvation. Both structures have been characterized by single‐crystal X‐ray analysis. The desolvated structure shows an interesting 3D porous structure with pendent ?NH2 groups inside the pore wall, whereas the solvated compound possesses a nonporous structure with DMF molecules on the metal centers. The amino group was postmodified through Schiff base condensation by pyridine‐2‐carboxaldehyde and palladium was anchored on that site. The modified framework has been utilized for the Suzuki cross‐coupling reaction. The compound shows high activity towards the C?C cross‐coupling reaction with good yields and turnover frequencies. Gas adsorption studies showed that the desolvated compound had permanent porosity and was microporous in nature with a BET surface area of 2052 m2 g?1. The material also possesses good CO2 (8 wt %) and H2 (1.87 wt %) adsorption capabilities.  相似文献   
34.
In many organic electronic devices functionality is achieved by blending two or more materials, typically polymers or molecules, with distinctly different optical or electrical properties in a single film. The local scale morphology of such blends is vital for the device performance. Here, a simple approach to study the full 3D morphology of phase‐separated blends, taking advantage of the possibility to selectively dissolve the different components is introduced. This method is applied in combination with AFM to investigate a blend of a semiconducting and ferroelectric polymer typically used as active layer in organic ferroelectric resistive switches. It is found that the blend consists of a ferroelectric matrix with three types of embedded semiconductor domains and a thin wetting layer at the bottom electrode. Statistical analysis of the obtained images excludes the presence of a fourth type of domains. The criteria for the applicability of the presented technique are discussed. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1231–1237  相似文献   
35.
36.
37.
38.
39.
Embedding endohdedral metallofullerenes (EMFs) into electron donor–acceptor systems is still a challenging task owing to their limited quantities and their still largely unexplored chemical properties. In this study, we have performed a 1,3‐dipolar cycloaddition reaction of a corrole‐based precursor with Sc3N@C80 to regioselectively form a [5,6]‐adduct ( 1 ). The successful attachment of the corrole moiety was confirmed by mass spectrometry. In the electronic ground state, absorption spectra suggest sizeable electronic communications between the electron acceptor and the electron donor. Moreover, the addition pattern occurring at a [5,6]‐bond junction is firmly proven by NMR spectroscopy and electrochemical investigations performed with 1 . In the electronically excited state, which is probed in photophysical assays with 1 , a fast electron‐transfer yields the radical ion pair state consisting of the one‐electron‐reduced Sc3N@C80 and of the one‐electron‐oxidized corrole upon its exclusive photoexcitation. As such, our results shed new light on the practical work utilizing EMFs as building blocks in photovoltaics.  相似文献   
40.
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