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   25199篇
  免费   2073篇
  国内免费   5189篇
化学   27158篇
晶体学   144篇
力学   396篇
综合类   121篇
数学   1043篇
物理学   3599篇
  2024年   66篇
  2023年   413篇
  2022年   709篇
  2021年   821篇
  2020年   1216篇
  2019年   1029篇
  2018年   1056篇
  2017年   969篇
  2016年   1058篇
  2015年   1003篇
  2014年   1555篇
  2013年   2451篇
  2012年   1471篇
  2011年   1748篇
  2010年   1327篇
  2009年   1474篇
  2008年   1554篇
  2007年   1740篇
  2006年   1487篇
  2005年   1380篇
  2004年   1362篇
  2003年   1051篇
  2002年   641篇
  2001年   516篇
  2000年   549篇
  1999年   471篇
  1998年   425篇
  1997年   372篇
  1996年   360篇
  1995年   337篇
  1994年   282篇
  1993年   237篇
  1992年   213篇
  1991年   167篇
  1990年   129篇
  1989年   132篇
  1988年   104篇
  1987年   61篇
  1986年   54篇
  1985年   61篇
  1984年   50篇
  1983年   27篇
  1982年   40篇
  1981年   36篇
  1980年   29篇
  1979年   27篇
  1978年   28篇
  1977年   29篇
  1976年   39篇
  1974年   38篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Monoalkynyl‐functionalized fullerene was precisely synthesized starting with pristine fullerene (C60) and characterized by multiple techniques. Methyl methacrylate and 6‐azido hexyl methacrylate were then randomly copolymerized via reversible addition fragmentation chain transfer polymerization to build polymer backbones with well‐controlled molecular weights and copolymer compositions. Finally, these two moieties were covalently assembled into a series of well‐defined side chain fullerene polymers (SFPs) via the copper‐mediated click reaction which was verified by Fourier transform infrared spectroscopy and 1H NMR. The fullerene loadings of the resultant polymers were estimated by thermogravimetric analysis and UV–vis spectroscopy, demonstrating consistent and high conversions in most of the samples. The morphology studies of the SFPs were performed both in solution and on solid substrates. Very intriguing self‐aggregation behaviors were detected by both gel permeation chromatography and dynamic light scattering analyses. Furthermore, the scanning electron microscopic images of these polymers showed the formation of various supramolecular nanoparticle assemblies and crystalline‐like clusters depending on the fullerene contents and polymer chain lengths. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3572–3582  相似文献   
92.
对氨基酚络合萃取机理的探讨   总被引:1,自引:0,他引:1  
魏凤玉  韦洪屹 《应用化学》2005,22(10):1155-0
对氨基酚络合萃取机理的探讨;对氨基酚; 络合萃取; 萃取机理; 萃取反应热  相似文献   
93.
李国锋  刘莹 《应用声学》1996,15(5):41-44
本文介绍了一种利用复倒谱来实现气声发音重建的方法。首先分析了气声发音的语音特征;进而在复倒谱序列中加入基频特征使其恢复到正常的语音。对元音[a]以及实际语音段进行了处理,均有较好的效果。  相似文献   
94.
95.
A practical, simple, and efficient method for the synthesis of pyrano-fused spirooxindoles via an organocatalytic three-component reaction of isatins, malononitrile, and dialkyl acetylenedicarboxylate in the presence of 3,4-dimethylaniline as an organocatalyst in ethanol is reported. The structures of these products are confirmed by IR, 1H NMR and 13C NMR spectroscopy, mass spectrometry, and single-crystal X-ray diffraction studies.  相似文献   
96.
A solid state metathesis (SSM) reaction was investigated with respect to the formation of rare‐earth carbodiimides, the role of the co‐produced salt (LiCl), and the eutectic flux medium (LiCl/KCl). A SSM reaction is characterized by an exothermic reaction in which a salt (often LiCl) is coproduced. When the salt melts, it can serve as a useful medium for the crystallization of a desired product. An improved crystal growth can be observed by using an eutectic flux. However, the composition of an eutectic LiCl/KCl flux is altered when LiCl is produced during the reaction. The thermal effects concerning the endothermic melting of the flux and the exothermic ingnition of the SSM reaction may compensate each other, which is not necessarily a drawback for the reaction to proceed.  相似文献   
97.
A four‐component reaction in the presence of Alum [KAl(SO4)2·12H2O] as an inexpensive and reusable catalyst using the ionic liquid as an effective green reaction media is reported.  相似文献   
98.
A bicyclo[2.2.2]octane C/D ring system,with a lactonic ring at C-8 and C-9,of the atisine-type C20-diterpenoid alkaloids,was successfully synthesized,using an oxidative dearomatization/intramolecular Diels-Alder reaction.  相似文献   
99.
An effective and environmentally benign benzylic oxidation for transition of alkylarenes into the corresponding carbonyl compounds was reported.Alkylarenes were mixed and stirred with potassium bromide,m-chloroperbenzoic acid and a catalytic amount of iodobenzene in water at 60 8C for several hours,a series of the corresponding carbonyl compounds was obtained in moderate to good yields.In the reaction,iodobenzene was first oxidized by m-chloroperbenzoic acid into the hypervalent iodine intermediate which then reacted with potassium bromide to form the key radical initiator for the benzylic oxidation.  相似文献   
100.
An expeditious synthesis of 2-aryl-benzimidazoles by the condensation of o-phenylenediamine with various araldehydes is described. This greener protocol is catalyzed by Amberlite IR-120, and proceeds efficiently in the absence of any organic solvent under microwave irradiation within 3–5 min.  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