全文获取类型
收费全文 | 374篇 |
免费 | 15篇 |
国内免费 | 60篇 |
专业分类
化学 | 388篇 |
晶体学 | 1篇 |
力学 | 14篇 |
综合类 | 1篇 |
数学 | 8篇 |
物理学 | 37篇 |
出版年
2024年 | 1篇 |
2023年 | 10篇 |
2022年 | 8篇 |
2021年 | 14篇 |
2020年 | 10篇 |
2019年 | 10篇 |
2018年 | 7篇 |
2017年 | 14篇 |
2016年 | 6篇 |
2015年 | 6篇 |
2014年 | 9篇 |
2013年 | 20篇 |
2012年 | 18篇 |
2011年 | 31篇 |
2010年 | 20篇 |
2009年 | 32篇 |
2008年 | 32篇 |
2007年 | 26篇 |
2006年 | 24篇 |
2005年 | 29篇 |
2004年 | 29篇 |
2003年 | 16篇 |
2002年 | 6篇 |
2001年 | 8篇 |
2000年 | 8篇 |
1999年 | 6篇 |
1998年 | 2篇 |
1997年 | 6篇 |
1996年 | 9篇 |
1995年 | 11篇 |
1994年 | 9篇 |
1993年 | 2篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 1篇 |
排序方式: 共有449条查询结果,搜索用时 46 毫秒
61.
Novel water-compatible molecularly imprinted polymers were synthesized in methanol-water systems with Tratarzine as template and 1-(α-methyl acrylate)-3-methylimidazolium bromide (1-MA-3MI-Br) as functional monomer, which has π-π hydrophobic, hydrogen-bonding and electrostatic interactions with template molecule. 1-MA-3MI-Br molecularly imprinted polymers (1-MA-3MI-Br-MIPs) were used as selective sorbents for the solid-phase extraction (SPE) of water-soluble acid dyes from wastewater and soft drink. The good linearity of the method was obtained in a range of 5.0-2000 μg/L with the correlation coefficient of > 0.999. The detection limits were in a range of 0.13-0.51 μg/L for the water-soluble acid dyes in wastewater and 0.095-0.84 μg/L for those in soft drink. The mean recoveries for the acid dyes are from 89.1% to 101.0% in spiked wastewater and 91.0-101.3% in spiked soft drink. Compared with strongly anion exchange solid phase extraction (SAX-SPE), mixture anion exchange solid phase extraction (MAX-SPE), and 1-MA-3MI-Br non-imprinted solid phase extraction (1-MA-3MI-Br-NISPE), almost all of the matrix interferences were removed by 1-MA-3MI-Br-MISPE, exhibiting higher selectivity, recovery and enrichment ability for the acid dyes and better baselines in the results of HPLC analysis. 相似文献
62.
A sensitive hydrophilic interaction liquid chromatography/electrospray ionization mass spectrometry (HILIC/ESI-MS/MS) method was developed for determination of selected aliphatic (i.e. malonic, succinic, glutaric, adipic, pimelic, suberic, azelaic, maleic, fumaric, glycolic and pyruvic acid), alicyclic (i.e. cis-pinonic and pinic acid) and aromatic (i.e. trimesic, phthalic acid and its isomers) carboxylic acids. Analytes were separated on an amide column using a gradient elution with a 10mM constant ionic strength mobile phase containing acetonitrile and aqueous ammonium acetate buffer (pH 5.0). The influence of the buffer type, pH, polar modifier and temperature on analyte retention under HILIC was studied. Static sonication-assisted solvent extraction was optimized for sample preparation prior to analysis. The recoveries obtained were higher than 90% for most analytes. The method was proven to be sensitive with limits of detection ranged from 0.03 to 16.0 μg/L in selected reaction monitoring mode (SRM). The repeatability and intermediate precision of the method, expressed as RSD (%) of the peak area ratio between analytes and their internal standards were generally lower than 5%. The method was successfully applied for determination of the studied acids in samples of ambient aerosol particles. A big advantage of the new method is also its ability to detect and separate the isobaric compounds of the selected carboxylic acids. Our results demonstrate that the method is specific and sensitive for the determination of a wider range of polar carboxylic acids at low concentrations in complex samples of aerosol particles. 相似文献
63.
64.
We have synthesized the low melting hygroscopic ionic liquid ethylammonium acetate (EAA) and characterized a concentrated solution of EAA as a reversed phase mobile phase replacement for organic solvents like methanol. This solution of EAA acts like an organic solvent with a polarity parameter (P=6.0) similar to methanol (P=5.1) but less than water (P=10.2). A test mixture of salicylate, nitrofurantoin, and acetophenone was separated in this order on C1, C4, and C18 columns using an EAA modified aqueous mobile phase. On a C-18 column, the reduction in retention factor for acetophenone from about 20 to 2 as the % EAA is raised from 20–80% is similar to the same trend found using methanol. However, the retention order using methanol is first nitrofurantoin, then salicylate, and finally acetophenone. Log retention factor (k) versus the volume fraction of either EAA or methanol plots were linear indicating the solvent strength parameter for EAA was about 85% of that for methanol. Despite the relatively high viscosity of EAA, plate count values averaged only about 15% less for EAA as compared to methanol using the same mobile phase composition and could be raised by either working at a temperature above ambient or reducing the flow rate. EAA as a modifier allowed for faster separations of water-soluble vitamins on a reversed phase column designed for totally 100% aqueous mobile phases.Acknowledgements This work was supported by a grant from the Miami University Committee on Faculty Research. We thank ES Industries for the gift of the AquaSep column. 相似文献
65.
用共振拉曼光谱研究电子激发态铜卟啉与DNA的相互作用 总被引:1,自引:0,他引:1
用共振拉曼光谱研究电子激发态铜卟啉与DNA的相互作用赵晓杰,江山,陆冬生,陆琳,毛慈波,安承武,范永昌,李再光(华中理工大学激光技术国家重点实验室武汉,430074)周翔,黄素秋(武汉大学化学系)关键词水溶性卟啉,受激复合物,DNA,共振拉曼光谱在卟... 相似文献
66.
Mounicou S Vonderheide AP Shann JR Caruso JA 《Analytical and bioanalytical chemistry》2006,386(5):1367-1378
Selenoproteins have been identified in a diverse range of organisms, including bacteria and animals. Their occurrence and
role in the plant kingdom are, however, less well-understood. This work investigated the water-soluble selenium-containing
proteins extracted from a selenium-accumulating plant species (Brassica juncea) and a nonaccumulator species (Helianthus annuus) exposed to varying forms and concentrations of selenium. Firstly, protein extracts were analyzed by size exclusion chromatography
coupled to inductively coupled plasma mass spectrometry; specific detection was achieved by monitoring characteristic isotopes.
Then, proteolytic digests of the plant extracts were analyzed by reversed phase chromatography coupled to ICP–MS in order
to investigate selenoamino acid and selenopeptide content. Selenomethionine was observed to be the primary constituent of
the proteins of the nonaccumulator plant, while selenocystine and selenomethionine were found in the same proportion in the
accumulator extract. One main selenium-containing species was present at higher levels in the root digests than in the leaf
digests; levels were greater in the nonaccumulator than in the accumulator plant. 相似文献
67.
Vikash Kumar Viraj G. Naik Avijit Das Sourayan Basu Bal Malabika Biswas Nupur Kumar Anasuya Ganguly Amrita Chatterjee Mainak Banerjee 《Tetrahedron》2019,75(27):3722-3732
Available online Development of water soluble AIE-active “light-up” bioprobes for the detection of biomacromolecules has drawn huge research interests in recent past. In this study, a series of ethylene glycol modified water soluble tetrameric tetraphenylethylene amphiphiles with pyridinium polar heads (TPE-xEG-Py, x = 3, 4, 6 or 1a-c) have been synthesized by varying the ethylene glycol spacer. Their unique structure allows them to form vesicles and other nanoaggregates in aqueous solutions. These amphiphiles were successfully utilized for fluorimetric detection and quantitation of BSA and DNA based on the electrostatic interactions to trigger AIE-emission from the TPE moiety. The electrostatic interaction was also proved very effective in wash-free imaging of both Gram-negative (E. coli) and Gram-positive (S. aureus) bacteria with up to 92 folds increase in fluorescence response within bacterial concentration 0–12 × 108 CFU mL?1. The strategy is advantageous due to cost-effective and easy synthesis, high water solubility, and fast response. 相似文献
68.
P. Ubbrìaco Angela Traini D. Manigrassi 《Journal of Thermal Analysis and Calorimetry》2008,92(1):301-305
The present research is concerning the characterization of FDR (fuel derived from residues) fly ash and mixtures with lime/brick
hydraulic binder by DTA/TG/DTG thermo-analysis, X-ray diffractometry and chemical analysis. The use of hydraulic binder obtained
from building brick rejects, which is less expensive than the usual solidifiers such as cementitious binder and silicates,
allows us to reutilize, in the meantime, this wreckage material, to the advantage of environmental sustainability. Fly ash
samples investigated in the present study were separated in a thermo-incineration plant. Mineralogical DTA/TG/DTG and XRD
investigations reveal the presence of different phases as well as chemical analysis shows a moderate concentration of heavy
metals and high content of chloride and sulphate. Results obtained from leaching tests with water carried out on hardened
pastes containing fly ash lead to interesting results, which highlight behaviour to the release of contaminants. The whole
of the results obtained in the present study make it possible to regard the objective of disposing such hardened materials
in inert waste landfill sites as achievable. 相似文献
69.
Sergey V. Kharlamov Rezeda K. Mukhitova Shamil K. Latypov Alexandr I. Konovalov 《Tetrahedron letters》2008,49(16):2566-2568
Here we report the design of a three-component supramolecular system in which a guest molecule reversibly translocates between two macrocyclic hosts. 相似文献
70.
Piotr Smoleński M.Fatima C. Guedes da Silva Armando J.L. Pombeiro 《Journal of organometallic chemistry》2008,693(13):2338-2344
The water-soluble RhI compound [Rh(Tpms)(CO)(PTA)] (1) (Tpms = O3SC(pz)3−, PTA = 1,3,5-triaza-7-phosphaadamantane) has been easily prepared in high yield by a single-pot reaction of [{Rh(CO)2(μ-Cl)}2] with PTA and the tris(1-pyrazolyl)methanesulfonate lithium salt Li(Tpms), in a CH2Cl2/MeOH solution at room temperature. This synthetic strategy can be easily applied to the preparation of general [Rh(Tpms)(CO)(L)] (L = phosphine) complexes and constitutes a substantial improvement over the previously described procedures. Compound 1 is air stable in the solid state and water-soluble, affording stable solutions under an inert atmosphere. It has been characterized by IR, 1H, 31P{1H} and 13C{1H} NMR spectroscopies, elemental and single crystal X-ray diffraction structural analyses. The solid state structure of 1 has a square-planar geometry with the Tpms ligand coordinating the metal centre in a (κ2: N,N) bipodal mode. The title compound has also been investigated by cyclic voltammetry in CH3CN, and values of the EL Lever and PL Pickett electrochemical parameters (which measure the ligand net electron-donor character) are proposed for the PTA ligand. Complex 1 represents the first example of a transition metal complex bearing both PTA and Tpms (or any other tris(1-pyrazolyl)methane or derivative) ligands. 相似文献