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   436589篇
  免费   5617篇
  国内免费   1252篇
化学   234825篇
晶体学   5947篇
力学   18837篇
综合类   14篇
数学   50371篇
物理学   133464篇
  2021年   3762篇
  2020年   4230篇
  2019年   4564篇
  2018年   5880篇
  2017年   5775篇
  2016年   8902篇
  2015年   5625篇
  2014年   8615篇
  2013年   20352篇
  2012年   15795篇
  2011年   19498篇
  2010年   13596篇
  2009年   13449篇
  2008年   17834篇
  2007年   17750篇
  2006年   16436篇
  2005年   14745篇
  2004年   13705篇
  2003年   12022篇
  2002年   11849篇
  2001年   13462篇
  2000年   10127篇
  1999年   7952篇
  1998年   6596篇
  1997年   6345篇
  1996年   6126篇
  1995年   5499篇
  1994年   5425篇
  1993年   5234篇
  1992年   5858篇
  1991年   5954篇
  1990年   5684篇
  1989年   5492篇
  1988年   5511篇
  1987年   5389篇
  1986年   4988篇
  1985年   6515篇
  1984年   6643篇
  1983年   5253篇
  1982年   5369篇
  1981年   5338篇
  1980年   4905篇
  1979年   5332篇
  1978年   5470篇
  1977年   5374篇
  1976年   5313篇
  1975年   4903篇
  1974年   4862篇
  1973年   4855篇
  1972年   3441篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
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   
103.
104.
105.
106.
107.
108.
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   
109.
Journal of Thermal Analysis and Calorimetry - In the present study, numerical simulations have been carried out on thermal characteristics and second-law analysis of turbulent Cu–H2O...  相似文献   
110.
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