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   706篇
  免费   3篇
  国内免费   13篇
化学   563篇
晶体学   2篇
力学   23篇
数学   61篇
物理学   73篇
  2023年   4篇
  2022年   7篇
  2021年   14篇
  2020年   27篇
  2019年   12篇
  2018年   19篇
  2017年   28篇
  2016年   21篇
  2015年   23篇
  2014年   62篇
  2013年   107篇
  2012年   38篇
  2011年   49篇
  2010年   45篇
  2009年   51篇
  2008年   39篇
  2007年   45篇
  2006年   24篇
  2005年   20篇
  2004年   21篇
  2003年   21篇
  2002年   8篇
  2001年   14篇
  2000年   4篇
  1999年   5篇
  1998年   7篇
  1997年   2篇
  1996年   1篇
  1995年   3篇
  1989年   1篇
排序方式: 共有722条查询结果,搜索用时 78 毫秒
51.
Research on Chemical Intermediates - In this research, synthesis and characterization of a novel Schiff base Cu (II) complex immobilized on Fe3O4@SiO2 nanoparticles are reported. Then, the...  相似文献   
52.
Research on Chemical Intermediates - The aim of present investigation is the synthesis of mesoporous catalyst based on hexagonal mesoporous silica. HMS support has exceptional properties such as...  相似文献   
53.
《Tetrahedron: Asymmetry》2014,25(22):1488-1493
The asymmetric cyclopropanation of a vinylphosphonate using optically active sulfonium and selenonium ylides derived from (−)-menthol and (+)-limonene was developed. The ylides were generated in situ by the reaction of the corresponding sulfonium or selenonium salt in the presence of potassium carbonate or DBU as a base. The transfer of the CHPh and CHCO2Et groups into the cyclopropane ring showed moderate diastereoselectivity and excellent enantioselectivity (up to 99:1) for the trans- and cis-products. The absolute configuration of phenyl cyclopropyl was assigned based on comparison to their tolyl analogues.  相似文献   
54.
在Mn髤模板作用下,2,6-diacetylpyridine(DAP)及合适链状胺化合物通过[1+1]环缩合反应,合成了3个大环席夫碱配合物,并进行了红外、元素分析、质谱及电导率等表征及研究。测得了配合物[MnL1(CH3CN)](ClO4)2的晶体结构,中心离子呈现出稍微扭曲的五角锥配位构型。研究了配合物对S.aureus(ATCC 6633),B.cereus(ATCC 7064),C.xerosis(ATCC 373)(gram-positive bacterial strains),E.coli(PTCC 10009),K.pneuomoniae(MTCC 109),and P.vulgaris(lio)(gram-negative bacterial strains)的抗菌活性。结果显示[MnL3](ClO4)2抗菌活性明显优于[MnL1(CH3CN)](ClO4)2and[MnL2](ClO4)2。在25℃条件下0.1 mol·L-1 KCl溶液中,通过电位计量法测定了化合物的质子化常数。  相似文献   
55.
The electrochemical synthesis of some new sulfonamide derivatives was carried out via the electrochemical oxidation of 2,3-dihydrophthalazine-l,4-dione (1) in the presence of arylsulfinic acids (2a and 2b) as nucleophiles. The results show that, the electrogenerated phthalazine-l,4-dione (lox) participates in a Michael type addition reaction with 2a or 2b and via an EC mechanism to produce the corresponding sulfonamide derivatives. This method provides a one-pot procedure for the synthesis of new sulfonamide derivatives of potential biological significance in good yields without using toxic reagents at a carbon electrode in an environmentally friendly manner.  相似文献   
56.
This study aims to optimize the formulation of composite films based on chicken skin gelatin with incorporation of rice starch (10–20%, w/w) and curcumin (0.03–0.10%, w/v). The effect of their interaction on film's tensile strength (TS), elongation at break (EAB), water vapor permeability (WVP) and antioxidant properties (DPPH%) were investigated using a response surface methodology-central composite design (RSM-CCD). The optimized film formulation was further validated to indicate the validity of the prediction model. The optimum conditions of the film were selected with incorporation of rice starch at 20% (w/w) and curcumin at 0.03% (w/v). The optimized film formulation has revealed better mechanical properties with low WVP value and good antioxidant activity. The results showed that optimized composite films formulation based on chicken skin gelatin with the incorporation of rice starch and curcumin has proving good validation of model prediction and can be effectively utilized in food packaging industry.  相似文献   
57.
Research on Chemical Intermediates - In this paper, tributyl(carboxymethyl)phosphonium bromotrichloroferrate as a new magnetic ionic liquid bearing acetic acid tags was synthesized and...  相似文献   
58.
A set of 2D finite element numerical simulation of induction heating process for an oxide Czochralski crystal growth system has been made for a range of f=1–100 kHz applied frequency of driving current. It was shown that the frequency selection has a marked effect in all basic induction phenomena, including electromagnetic field distribution, skin depth, coil efficiency, and intensity and structure of heating in the growth setup.  相似文献   
59.
60.
A simple, precise, sensitive and accurate method was developed for rapid determination of trace quantities of periodate. The method is based on the accelerating effect of periodate on the reaction of bromate and hydrochloric acid in the presence of hydrazine. The decolorization of methyl orange with the reaction products was used to monitor the reaction spectrophotometrically at 525 nm. Periodate could be determined in the concentration ranges of 0.02–1.5 g/mL. The relative standard deviation for ten replicate determinations of 0.3 g/mL of periodate was 1.12%. The method was applied to the determination of periodate in water samples and indirect determination of ethylene glycol in gasoline and glycerol in vegetable oil via Malaprade reaction with satisfactory results.  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