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   552247篇
  免费   8553篇
  国内免费   4839篇
化学   280322篇
晶体学   7643篇
力学   27190篇
综合类   185篇
数学   91180篇
物理学   159119篇
  2021年   4491篇
  2020年   4910篇
  2019年   5242篇
  2018年   17156篇
  2017年   17128篇
  2016年   15997篇
  2015年   7810篇
  2014年   10300篇
  2013年   22810篇
  2012年   23572篇
  2011年   32694篇
  2010年   21246篇
  2009年   21513篇
  2008年   25590篇
  2007年   27248篇
  2006年   18118篇
  2005年   20803篇
  2004年   19648篇
  2003年   16677篇
  2002年   13897篇
  2001年   14218篇
  2000年   10778篇
  1999年   8427篇
  1998年   7037篇
  1997年   6697篇
  1996年   6474篇
  1995年   5771篇
  1994年   5612篇
  1993年   5453篇
  1992年   6100篇
  1991年   6165篇
  1990年   5865篇
  1989年   5656篇
  1988年   5668篇
  1987年   5509篇
  1986年   5220篇
  1985年   6696篇
  1984年   6817篇
  1983年   5410篇
  1982年   5483篇
  1981年   5460篇
  1980年   5051篇
  1979年   5443篇
  1978年   5578篇
  1977年   5444篇
  1976年   5414篇
  1975年   4973篇
  1974年   4949篇
  1973年   4953篇
  1972年   3515篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
63.
64.
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   
65.
66.
67.
68.
69.
70.
In the current work, two eco‐friendly analytical methods based on capillary electrophoresis (CE) and reversed phase liquid chromatography (RPLC) were developed for simultaneous determination of the most commonly used anticancer drugs for Hodgkin's disease: methotrexate (MTX), vinblastine, chlorambucil and dacarbazine. A background electrolyte (BGE) of 12.5 mmol/L phosphate buffer at pH 7.4 and 0.1 µmol/L 1‐butyl‐3‐methyl imidazolium bromide (BMImBr) ionic liquid (IL) was used for CE measurements at 250 nm detection wavelength, 20 kV applied voltage and 25 °C. The rinsing protocol was significantly improved to reduce the adsorption of IL on the interior surface of capillary. Moreover, RPLC method was developed on α‐1‐acid glycoprotein (AGP) column. Mobile phase was 10 mmol/L phosphate buffer at pH 6.0 (100% v/v) and flow rate at 0.1 mL/min. As AGP is a chiral column, it was successfully separated l ‐MTX from its enantiomer impurity d ‐MTX. Good linearity of quantitative analysis was achieved with coefficients of determinations (r2) >0.995. The stability of drugs measurements was investigated with adequate recoveries up to 24 h storage time under ambient temperature. The limits of detection were <50 and 90 ng/mL by CE and RPLC, respectively. The using of short‐chain IL as an additive in BGE achieved 600‐fold sensitivity enhancement compared with conventional Capillary Zone Electrophoresis (CZE). Therefore, for the first time, the proposed methods were successfully applied to determine simultaneously the analytes in human plasma and urine samples at clinically relevant concentrations with fast and simple pretreatments. Developed IL‐assisted CE and RPLC methods were also applied to measure MTX levels in patients’ samples over time. Copyright © 2014 John Wiley & Sons, Ltd.  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