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   443001篇
  免费   5847篇
  国内免费   1283篇
化学   239210篇
晶体学   6564篇
力学   18969篇
综合类   13篇
数学   51129篇
物理学   134246篇
  2021年   3841篇
  2020年   4329篇
  2019年   4654篇
  2018年   5960篇
  2017年   5837篇
  2016年   9053篇
  2015年   5759篇
  2014年   8761篇
  2013年   20599篇
  2012年   16242篇
  2011年   19952篇
  2010年   13835篇
  2009年   13588篇
  2008年   18179篇
  2007年   18087篇
  2006年   16829篇
  2005年   15112篇
  2004年   13982篇
  2003年   12281篇
  2002年   12074篇
  2001年   13513篇
  2000年   10170篇
  1999年   7998篇
  1998年   6647篇
  1997年   6397篇
  1996年   6173篇
  1995年   5540篇
  1994年   5474篇
  1993年   5257篇
  1992年   5886篇
  1991年   5982篇
  1990年   5707篇
  1989年   5499篇
  1988年   5531篇
  1987年   5403篇
  1986年   5108篇
  1985年   6632篇
  1984年   6736篇
  1983年   5327篇
  1982年   5438篇
  1981年   5419篇
  1980年   4998篇
  1979年   5397篇
  1978年   5530篇
  1977年   5423篇
  1976年   5354篇
  1975年   4946篇
  1974年   4905篇
  1973年   4897篇
  1972年   3458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