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   468530篇
  免费   6685篇
  国内免费   1262篇
化学   252894篇
晶体学   6570篇
力学   19340篇
综合类   14篇
数学   57587篇
物理学   140072篇
  2021年   4164篇
  2020年   4743篇
  2019年   5036篇
  2018年   6600篇
  2017年   6413篇
  2016年   10137篇
  2015年   6626篇
  2014年   9558篇
  2013年   22492篇
  2012年   17738篇
  2011年   21229篇
  2010年   14834篇
  2009年   14514篇
  2008年   19357篇
  2007年   19104篇
  2006年   17648篇
  2005年   15977篇
  2004年   14707篇
  2003年   12907篇
  2002年   12559篇
  2001年   13994篇
  2000年   10684篇
  1999年   8347篇
  1998年   6922篇
  1997年   6623篇
  1996年   6506篇
  1995年   5780篇
  1994年   5780篇
  1993年   5547篇
  1992年   6194篇
  1991年   6201篇
  1990年   5984篇
  1989年   5746篇
  1988年   5754篇
  1987年   5601篇
  1986年   5317篇
  1985年   6881篇
  1984年   6991篇
  1983年   5545篇
  1982年   5634篇
  1981年   5628篇
  1980年   5164篇
  1979年   5559篇
  1978年   5684篇
  1977年   5575篇
  1976年   5536篇
  1975年   5103篇
  1974年   5028篇
  1973年   5050篇
  1972年   3544篇
排序方式: 共有10000条查询结果,搜索用时 288 毫秒
121.
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   
122.
123.
124.
125.
126.
127.
128.
129.
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   
130.
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   
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