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   538篇
  免费   55篇
  国内免费   91篇
化学   563篇
晶体学   2篇
力学   8篇
综合类   5篇
数学   33篇
物理学   73篇
  2023年   2篇
  2022年   1篇
  2019年   1篇
  2017年   2篇
  2016年   4篇
  2015年   1篇
  2014年   32篇
  2013年   52篇
  2012年   45篇
  2011年   8篇
  2010年   2篇
  2009年   4篇
  2008年   23篇
  2007年   20篇
  2006年   16篇
  2005年   22篇
  2004年   31篇
  2003年   40篇
  2002年   89篇
  2001年   194篇
  2000年   31篇
  1999年   24篇
  1998年   13篇
  1997年   11篇
  1996年   3篇
  1995年   4篇
  1994年   4篇
  1993年   1篇
  1992年   1篇
  1991年   2篇
  1990年   1篇
排序方式: 共有684条查询结果,搜索用时 15 毫秒
41.
A rapid and sensitive method for the analysis of three catecholamines by capillary electrophoresis(CE)with directchemiluminescence(CL)detection is described.The detection limits(S/N=3)were 1.3*10-8g/mL for isoprenaline,1.0*10-8g/mL for epinephrine and 2.8*10-8g/mL for dopamine.The proposed method was successfully applied to theanalysis of catecholamines in urine samples of cigarette smokers and nonsmokers.The results showed that there is a close relationbetween the release of dopamine in human body fluids and cigarette smoking/nonsmoking.  相似文献   
42.
To enable insulin as multi-drug carrier, we designed and synthesized dendritic linker molecule bearing three 5-Fluorouracil residues at the branch ends. The new conjugate showed excellent water solubility. The stabilities under different conditions were investigated. The results showed that the conjugate was a potential prodrug to release free 5-Fu.  相似文献   
43.
股票价格波动的塑性性质及模型探讨   总被引:1,自引:0,他引:1  
首先基于股票价格和成交量,根据股票的量价规律,分析了股价波动的塑性性质;然后使用计量经济学方法建立描述股价波动的塑性模型,包括股价塑性基本模型、基本模型的一阶自回归模型、幂指数模型及幂指数模型的一阶自回归模型,基于12支样本股对这些模型进行参数估计和检验;最后对4种形式的股价塑性模型进行了总结。由4种模型均能够通过经济学检验和统计学检验可知股价波动具有塑性性质,且幂指数模型描述股价塑性较为科学、合理。  相似文献   
44.
Benzimidazole compounds have attracted a renewed interest recently owing to theirpotential applications in high-performance composite materials, electronic chemicals,photosensitive materials, and their special potentials in biological and/or medicinalapplication1,2. Typically, aromatic compounds with near planar structures and contain-ing hydrogen-donor groups or groups, which are capable of being protonated, havespecial interactions with DNA via intercalation, hydrogen-bonding, and so on3.Me…  相似文献   
45.
Two different skeletons of heterocyclic compounds,quinoline and quinazolinone analogs could be obtained by a novel one-pot synthesis from substituted 3-amino-1 H-benzo[f]chromene-2-carbonitrile derivatives and cyclohexanone in DMF in the catalyst of anhydrous zinc chloride under reflux.A plausible mechanism was proposed.  相似文献   
46.
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   
47.
Andrographolide (Andro) (Figure 1) is a diterpene lactone isolated from Andrographis paniculate Nees1. It has showed several biological activities including analgesic, antipyretic and anti-inflammatory effects2. However, its poor water solubility and unstability towards oxygen restrained its application. In pharmaceutics, b-CD is used to increase solubility and stability3. We have prepared the inclusion compound of Andro/b-CD (Figure 2) under microwave irradiation4. It has been found…  相似文献   
48.
In our early researches, lanthanum and cerium could enter plant and bind to porphyrin of chlorophyll to form Ln3+-chllorophyll. La and Ce greatly increase photosystem II (PSII) activity and PSII electron transport rate, and the fluorescence emission peaks of PSII are blue-shifted [1—4]. Do REEs coordinate with PSII reaction center complex in vivo? Moreover, do REEs coordinate with D1(30 kD)/D2(32 kD)/Cytb559 (~9 kD) reaction center complex of site of producing pri-mary reaction-p…  相似文献   
49.
Wittigreactionisoneofthemostimportantmethodfortheformationofcarbon-carbondoublebondandhasbeenwidelyusedinthesynthesisofnaturalproducts1,2.Recentlyitwasfoundthatalcoholscanundergoinsituoxidation-Wittigreactionwithphosponiumylidestogivecorrespondingolefinationproducts,whichhasgreatpotentialutilitiesinorganicsynthesis3.Tosimplifytheprocedureofthereactionfurther,weconsideredtocombinethedeprotonationofylide,oxidationofalcoholandWittigreactionintoonetandemreaction.Weutilizedphosphoniumorarsoniumsal…  相似文献   
50.
~~Formation of α,α'-Bis(substituted benzylidene)cycloalkanones from Masked Aldehydes Promoted by Samarium(III) Triiodide~~  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