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   338篇
  免费   6篇
  国内免费   2篇
化学   190篇
晶体学   1篇
力学   24篇
数学   85篇
物理学   46篇
  2024年   1篇
  2023年   2篇
  2022年   19篇
  2021年   26篇
  2020年   9篇
  2019年   9篇
  2018年   8篇
  2017年   7篇
  2016年   7篇
  2015年   8篇
  2014年   9篇
  2013年   18篇
  2012年   24篇
  2011年   27篇
  2010年   17篇
  2009年   12篇
  2008年   24篇
  2007年   12篇
  2006年   12篇
  2005年   25篇
  2004年   8篇
  2003年   14篇
  2002年   8篇
  2001年   7篇
  2000年   3篇
  1999年   2篇
  1998年   2篇
  1997年   1篇
  1996年   4篇
  1995年   3篇
  1994年   5篇
  1992年   2篇
  1990年   1篇
  1989年   2篇
  1988年   2篇
  1985年   1篇
  1984年   3篇
  1983年   1篇
  1976年   1篇
排序方式: 共有346条查询结果,搜索用时 15 毫秒
21.
A series of soluble conjugated ligands TT , FT , PT , and NT that contained terpyridyl terminal units were synthesized by Heck coupling. These ligands absorbed at 341–434 nm and emitted blue–green light, with maximum at 440–522 nm and photoluminescence quantum yields of 0.15–0.71 in solution. The double‐layer electroluminescent devices with the configuration of ITO/PEDOT/ligand FT , PT , or NT /Ca/Al exhibited a brightness of 43–63 cd/m2. These ligands were further reacted with zinc(II) and ruthenium(II) ions and subsequent anion exchange to afford linear and supramolecular complexes. The photophysics of these complexes were investigated. A significant redshift of the emission maximum of the Zn complexes relative to the corresponding ligands was observed. The Ru complexes were used to fabricate photovoltaic devices with the structure ITO/PEDOT/Ru complex/P3HT:PCBM (1:1 wt/wt)/Ca/Al. The power conversion efficiency of these polymer–fullerene bulk heterojunction photovoltaic devices was up to 0.71%. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7702–7712, 2008  相似文献   
22.
The 232Th-uptake ([Th(IV)]° = 9.7 × 10?5 M) from carbonate solutions ([CO 3 2 ]tot = 0.25 M, 9.0 < pHc < 10.8) by raw and HDTMA-modified HEU-type zeolitic-, chabazitic- and phillipsitic-tuffs was investigated. The strong uptake by the HDTMA-tuffs at pHc≈9 was assigned to the Th(CO3) 5 6? and ThOH(CO3) 4 5? predominance. The sorption coefficients (R d) decreased with increasing pHc indicating carbonate competition. Enhanced R d values for pHc > 10.5 are likely due to ThO2(am)-precipitation. The 237Np-uptake ([Np(V)]° = 2.6 × 10?5 M) from carbonate solutions ([CO 3 2 ]tot = 0.25 and 3.0 × 10?4 M) by raw and HDTMA-modified HEU-type zeolitic tuff and pulverized pure heulandite crystals was studied under Ar-atmosphere at 6 < pHc < 11. The R d values for both elements indicated the modified tuffs potential to remove tetravalent- and pentavalent actinides from environmental matrices.  相似文献   
23.
The fragmentation characteristics of peptides derivatized at the side-chain ε-amino group of lysyl residues via reductive amination with benzaldehyde have been examined using collision-induced dissociation (CID) tandem mass spectrometry. The resulting MS/MS spectra exhibit peaks representing product ions formed from two independent fragmentation pathways. One pathway results in backbone fragmentation and commonly observed sequence ion peaks. The other pathway corresponds to the unsymmetrical, heterolytic cleavage of the Cζ-Nε bond that links the benzyl derivative to the side-chain lysyl residue. This results in the elimination of the derivative as a benzylic or tropylium carbocation and a (n − l)+-charged peptide product (where n is the precursor ion charge state). The frequency of occurrence of the elimination pathway increases with increasing charge of the precursor ion. For the benzylmodified tryptic peptides analyzed in this study, peaks representing products from both of these pathways are observed in the MS/MS spectra of doubly-charged precursor ions, but the carbocation elimination pathway occurs almost exclusively for triply-charged precursor ions. The experimental evidence presented herein, combined with molecular orbital calculations, suggests that the elimination pathway is a charge-directed reaction contingent upon protonation of the secondary ε-amino group of the benzyl-derivatized lysyl side chain. If the secondary ε-amine is protonated, the elimination of the carbocation is observed. If the precursor is not protonated at the secondary ε-amine, backbone fragmentation persists. The application of appropriately substituted benzyl analogs may allow for selective control over the relative abundance of product ions generated from the two pathways.  相似文献   
24.
25.
26.
27.
A straightforward size exclusion chromatography (SEC) method was developed and validated for the determination of total polivinylpyrrolidone (PVP) in ophthalmic solutions using the unusual combination of size exclusion chromatography (SEC), ultraviolet-visible detection and quantitation of an analyte peak that elutes in the total exclusion volume of the column. Samples of opthalmic solutions are diluted with water and injected onto a TSKgel G1000PW, 7.5 mm i.d. × 30 cm, 12 μm column at 50°C, with 80:20 0.1M sodium acetate-methanol mobile phase and UV detection at 220 nm. Validation was successful for a stability indicating pharmaceutical method, with parameters including specificity, accuracy, linearity, and precision within typical pharmaceutical acceptance criteria. A stress study with acid, base, peroxide, heat, and light indicates that there is no interference from drug, product, or excipients.  相似文献   
28.
Aliskiren is a nonpeptide antihypertensive drug that potently inhibits the human enzyme renin in vitro and in vivo. Many clinical trials have shown the efficacy of aliskiren to lower blood pressure in correlation with other antihypertensive agents. In this report, the conformational behavior of aliskiren is studied in water, trifluoroethanol, and dimethylformamide solutions by means of 2D-NMR spectroscopy and molecular dynamics simulations. The stereochemical characteristics of aliskiren in different solutions, in combination with the previously published crystal structure of the renin-aliskiren complex have been investigated. The aim of this study was to explore the conformational behavior of this first successful renin inhibitor in relation to its environment. In aqueous solution, aliskiren adapts a U-shape conformation, whereas in DMF, the molecule is basically endowed with an "extended" conformation, which has more similarities to the one bound to the receptor.  相似文献   
29.
A study of two dihydroxybenzoic acid isomers shows that computational methods can be used to predict hydrate formation, the compound:water ratio and hydrate crystal structures. The calculations also help identify a novel hydrate found in the solid form screening that validates this study.  相似文献   
30.
We fabricated a TiO(2)-ZrO(2) affinity chromatography micro-column on 2 mm PMMA plates, and demonstrated the enrichment and separation of (a) a standard mono- and tetra-phosphopeptide, and (b) phosphopeptides contained in a tryptic digest of β-Casein. The chromatography column consisted of 32 parallel microchannels with common input and output ports and was fabricated by lithography directly on the polymeric substrate followed by plasma etching (i.e. standard MEMS processing) and sealed with lamination. The liquid deposited TiO(2)-ZrO(2) stationary phase was characterized by X-ray diffraction and was found to be mostly TiO(2) and ZrO(2) in crystalline phases. Off-chip UV detection and MALDI MS identification of the separated effluents were used. The chip had a capacity of >1.4 μg (0.7 nmol) of a prototype mono-phosphopeptide and a recovery of 94 ± 3%, and can be used with small samples (less than 0.1 μL depending on the syringe pump used). The chip design allows an expansion of its capacity by means of increasing the number of parallel microchannels at a constant sample volume. Our approach provided an alternative to off-line extraction tips (with typical capacities of 1-2 μg and sample volumes of 1-10 μL), and to on-chip efforts based on packed bed and frit formats.  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