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   531974篇
  免费   6419篇
  国内免费   1534篇
化学   286450篇
晶体学   7972篇
力学   23254篇
综合类   16篇
数学   61237篇
物理学   160998篇
  2021年   4415篇
  2020年   4948篇
  2019年   5316篇
  2018年   6870篇
  2017年   6788篇
  2016年   10434篇
  2015年   6604篇
  2014年   10075篇
  2013年   24379篇
  2012年   18804篇
  2011年   23013篇
  2010年   16173篇
  2009年   16123篇
  2008年   21246篇
  2007年   21011篇
  2006年   19704篇
  2005年   17667篇
  2004年   16311篇
  2003年   14538篇
  2002年   14321篇
  2001年   16680篇
  2000年   12510篇
  1999年   9795篇
  1998年   7934篇
  1997年   7732篇
  1996年   7476篇
  1995年   6759篇
  1994年   6657篇
  1993年   6316篇
  1992年   7252篇
  1991年   7420篇
  1990年   7060篇
  1989年   6864篇
  1988年   6885篇
  1987年   6746篇
  1986年   6291篇
  1985年   8147篇
  1984年   8319篇
  1983年   6591篇
  1982年   6715篇
  1981年   6559篇
  1980年   6160篇
  1979年   6773篇
  1978年   6972篇
  1977年   6850篇
  1976年   6743篇
  1975年   6207篇
  1974年   6210篇
  1973年   6280篇
  1972年   4375篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
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   
43.
44.
45.
46.
47.
48.
49.
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   
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