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   517篇
  免费   49篇
  国内免费   83篇
化学   535篇
力学   18篇
综合类   5篇
数学   28篇
物理学   63篇
  2020年   2篇
  2019年   1篇
  2018年   1篇
  2017年   1篇
  2015年   2篇
  2014年   29篇
  2013年   47篇
  2012年   43篇
  2011年   9篇
  2010年   2篇
  2009年   6篇
  2008年   22篇
  2007年   19篇
  2006年   18篇
  2005年   22篇
  2004年   30篇
  2003年   36篇
  2002年   85篇
  2001年   193篇
  2000年   34篇
  1999年   20篇
  1998年   11篇
  1997年   8篇
  1996年   1篇
  1995年   4篇
  1988年   1篇
  1986年   1篇
  1985年   1篇
排序方式: 共有649条查询结果,搜索用时 0 毫秒
81.
Polymer-supported reagents for organic synthesis are enjoying a renewed popularity with the emergence of combinatorial chemistry in recent years1. 4-(Arylseleno)morpholines formed in situ are useful -seleno-introducing reagents for saturated aldehydes2. -Sele- noaldehydes, as a frequently used intermediates, can be converted into -haloaldehydes by halogenating reaction3. However, organic selenium reagents always have a foul smell and are quite toxic, which is often problematic in organic sy…  相似文献   
82.
The photochemistry of the vitamin D family and their precursors has been the subject of extensive studies for many years1-4. Most of the studies focus on the photoisomer- ization of 7-dehydrocholesterol and that of tachysterol to previtamin D3, which is of commercial importance in the synthesis of vitamin D34, 5. Recently the cis/trans isomerization of vitamin D analogs (Scheme 1) draws attention because of its importance in the synthesis of hydroxylated vitamin D metabolites6. However, o…  相似文献   
83.
The similar electrochemical oxidation behaviors of hydroxypivalaldehyde in ionic liquids (ILs) medium, C4MIMPF6, C4MIMBF4 and CsMIMPF6, are investigated using classic electrochemical methods, respectively. Only the product, hydroxypivalic acid is detected by high performance liquid chromatography (HPLC). It can be conferred that the electrochemical oxidation of hydroxypivalaldehyde consists of two successive one-electron irreversible reactions at glass carbon (GC) electrode and the possible reaction mechanism in the ILs is proposed firstly. The diffusion coefficients of hydroxypivalaldehyde are obtained according to the electrochemical characteristics of hydroxypivalaldehyde in C4MIMPF6, C4MIMBF4 and CsMIMPF6.  相似文献   
84.
A new amperometric biosensor for hydrogen peroxide was developed based on adsorption of horseradish peroxidase at the glassy carbon electrode modified with zinc oxide nanoflowers produced by electrodeposition onto multi-walled carbon nanotubes (MWNTs) film. The morphology of the MWNTs/nano-ZnO electrode has been investigated by scanning electron microscopy (SEM), and the electrochemical performance of the electrode has also been studied by amperometric method. The resulting electrode offered an excellent detection for hydrogen peroxide at -0.11 V with a linear response range of 9.9×10^-7 to 2.9×10^-3 mol/L with a correlation coefficient of 0.991, and response time 〈5 s. The biosensor displays rapid response and expanded linear response range, and excellent stability.  相似文献   
85.
~~Formation of α,α'-Bis(substituted benzylidene)cycloalkanones from Masked Aldehydes Promoted by Samarium(III) Triiodide~~  相似文献   
86.
Great attention is currently paid to the synthesis of polynuclear transition metal complexes as well as their photochemical, photophysical, and electrochemical properties. The design of multicomponent systems capable of performing useful light- and/or redox-induced function is of special interest1. The oxo-centered carboxylate-bridge trinuclear ruthenium clusters have been investigated extensively during recent decades because they have remarkable electron-transfer properties, intense visibl…  相似文献   
87.
IBONACCISEQUENCEANDCANTOR′STERNARYSETTONGJINGCHENGSAMONS,J.ManuscriptreceivedSeptember12,1994.RevisedDecember15,1996.Depar...  相似文献   
88.
本文研究了ICP-AES直接粉末法分析中一些主要因素(诸如:ICP电学参数、载气流量、单位时间进样量及试样成分等)对谱线强度的影响问题。作者指出,分析过程中上述因素常发生非人为所能控制之变化,谱线强度亦随之改变,所造成的分析误差,可藉助缓冲和内标的作用加以减弱或消除。文中以大量实验数据阐明了ICP-AES直接粉末法分析中缓冲剂和内标的作用并提出了供参考的选择原则。  相似文献   
89.
在C60单晶(111)解理面上制备出厚度约30 nm的K3C60单晶膜.利用同步辐射光源,在低温下(约150K)测量了样品法向发射的角分辨光电子谱.观察到K3C60导带和价带明显的色散.导带的光电子谱峰可清晰分辨出4个子峰,这些子峰的最大色散超过0.5eV,并且色散曲线与K3C60的一维无序晶体结构模型下的能带理论基本吻合,只是子带间隔差异较大.  相似文献   
90.
New type of spherical pore Al alloy foam with low porosity and high strength   总被引:15,自引:0,他引:15  
The Ultra Light Metal Structure with variouskinds of pores (open, close) realizes the lightness andmultifunction of structural material. The functionsinclude lightness (ρ < 1), high specific strength, highenergy absorption, sound insulation, heat insulationand electromagnetism shield. It is one of the hotspotsin material research nowadays[1— . The requirements 6]of high speed movement and high technology make Alalloy foam, which has higher specific st…  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