全文获取类型
收费全文 | 346篇 |
免费 | 25篇 |
国内免费 | 1篇 |
专业分类
化学 | 300篇 |
晶体学 | 3篇 |
力学 | 3篇 |
数学 | 31篇 |
物理学 | 35篇 |
出版年
2023年 | 4篇 |
2022年 | 7篇 |
2021年 | 8篇 |
2020年 | 6篇 |
2019年 | 7篇 |
2018年 | 8篇 |
2017年 | 5篇 |
2016年 | 16篇 |
2015年 | 15篇 |
2014年 | 18篇 |
2013年 | 20篇 |
2012年 | 43篇 |
2011年 | 35篇 |
2010年 | 16篇 |
2009年 | 13篇 |
2008年 | 19篇 |
2007年 | 27篇 |
2006年 | 13篇 |
2005年 | 14篇 |
2004年 | 20篇 |
2003年 | 24篇 |
2002年 | 5篇 |
2001年 | 1篇 |
1999年 | 2篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1972年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有372条查询结果,搜索用时 0 毫秒
71.
Gourier D Binet L Scrzypczak A Derenne S Robert F 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2004,60(6):1349-1357
The insoluble organic matter (IOM) of three carbonaceous meteorites (Orgueil, Murchison and Tagish Lake meteorites) and three samples of cherts (microcrystalline SiO2 rock) containing microfossils with age ranging between 45 million years and 3.5 billion years is studied by electron paramagnetic resonance (EPR). The age of the meteorites is that of the solar system (4.6 billion years). The purpose of this work was to determine the EPR parameters, which allow us to discriminate between biogenic and extra terrestrial origin for the organic matter. Such indicators should be relevant for the controversy regarding the biogenicity of the organic matter in the oldest cheroot (3.5 billion years) and in Martian meteorites containing microbe-like microstructures. The organic matter of meteorites contains a high concentration of diradicaloid moieties characterised by a diamagnetic ground state S = 0 and a thermally accessible triplet state S = 1. The three meteorites exhibit the same singlet-triplet gap (ST gap) DeltaE approximately 0.1 eV. To the best of our knowledge, such diradicaloids are unknown in insoluble organic matter of terrestrial origin. We have also shown that the EPR linewidth of insoluble organic matter in cherts and coals decrease logarithmically with the age of the organic matter. We conclude from this result that the organic matter in the oldest cherts (3.5 billion years) has the same age as their SiO2 matrix, and is not due to a latter contamination by bacteria, as was recently found in meteoritic samples. 相似文献
72.
Beattie DA Beaussart A Mierczynska-Vasilev A Harmer SL Thierry B Puskar L Tobin M 《Langmuir : the ACS journal of surfaces and colloids》2012,28(3):1683-1688
Synchrotron FTIR microscopy has been used to probe the structure of model boundary lubricant layers confined at the solid-solid interface. The combination of high brightness of the IR source and a novel contact geometry that uses a hemispherical internal reflection element as the means for light delivery has enabled the detection of <2.5 nm thin monolayer lubricant layers in the solid-solid contact, in addition to allowing for spectral acquisition from specific regions of the contact. Spectra of hydration water from within a confined polyelectrolyte multilayer film have also been acquired, highlighting the altered hydrogen bonding environment within the polymer layer. 相似文献
73.
Energetic and spectral properties of triple photon downconversion in a phase-matched KTiOPO4 crystal
Dot A Borne A Boulanger B Segonds P Félix C Bencheikh K Levenson JA 《Optics letters》2012,37(12):2334-2336
We measured the spectrum and energy of infrared triple photons generated in a phase-matched KTiOPO4 crystal pumped by picosecond beams at 532 and 1662 nm. The experimental data are in good agreement with our model, taking into account the spectral linewidths of the incident beams as well as a parasitic Kerr effect. 相似文献
74.
C Boyère AF Léonard B Grignard A Favrelle JP Pirard M Paquot C Jérôme A Debuigne 《Chemical communications (Cambridge, England)》2012,48(67):8356-8358
Highly porous materials were produced by acrylamide polymerisation templated by supercritical CO(2)-in-water emulsions using new fluorinated glycosurfactants. Properties of the resulting polymer scaffolds were tuned by performing dispersion polymerisations within their cavities filled with supercritical CO(2). 相似文献
75.
Gaulier C Hospital A Legeret B Delmas AF Aucagne V Cisnetti F Gautier A 《Chemical communications (Cambridge, England)》2012,48(33):4005-4007
A reducing agent-free version of CuAAC able to operate under open air conditions is reported. A readily-synthesizable, hydrophilic and highly stable Cu(I)-NHC allows the clean ligations of unprotected peptides comprising sensitive side chains, at millimolar concentrations. 相似文献
76.
Hudson R Rivière A Cirtiu CM Luska KL Moores A 《Chemical communications (Cambridge, England)》2012,48(27):3360-3362
We report for the first time the use of iron-iron oxide core-shell nanoparticles for the hydrogenation of olefins and alkynes under mild conditions in ethanol and in an aqueous medium. This catalyst proves robust towards the presence of oxidants, such as oxygen and water, is magnetically recoverable and shows selectivity towards the less activated double bonds. 相似文献
77.
Audrey Alesandra Stinghen Garcia Lonni Renata Longhini Gisely Cristiny Lopes João Carlos Palazzo de Mello Ieda Spacino Scarminio 《Analytica chimica acta》2012
Statistical design mixtures of water, methanol, acetone and ethanol were used to extract material from Trichilia catigua (Meliaceae) barks to study the effects of different solvents and their mixtures on its yield, total polyphenol content and antioxidant activity. The experimental results and their response surface models showed that quaternary mixtures with approximately equal proportions of all four solvents provided the highest yields, total polyphenol contents and antioxidant activities of the crude extracts followed by ternary design mixtures. Principal component and hierarchical clustering analysis of the HPLC–DAD spectra of the chromatographic peaks of 1:1:1:1 water–methanol–acetone–ethanol mixture extracts indicate the presence of cinchonains, gallic acid derivatives, natural polyphenols, flavanoids, catechins, and epicatechins. 相似文献
78.
Audrey Devatine Jean Paul Canselier Nadine Gabas Joël Jaud 《Journal of chemical crystallography》2003,33(2):85-90
The new crystal and molecular structures of a less common hydrated calcium L(–)-malate (calcium (2S) 2-hydroxybutanedioate trihydrate) Ca(C4H4O5)3H2O, are reported. X-ray crystallographic data are as follows: a = 6.6460(3) Å, b = 8.3795(3) Å, c = 8.2707(4) Å, = 112.640(2)°, V = 425.1(4) Å3, space group P21 (No. 4), Z = 2, D
calc = 1.767 g cm–3. The calcium ion coordination number is seven. One of the three water molecules present in the unit cell is less strongly bound, only interacting with a calcium ion. In aqueous or hydroalcoholic solution, both di- and trihydrated species crystallize simultaneously. 相似文献
79.
80.
Dr. Audrey Llevot Patrick‐Kurt Dannecker Marc von Czapiewski Lena C. Over Zafer Söyler Prof. Dr. Michael A. R. Meier 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(33):11510-11521
Taking advantage of the structural diversity of different biomass resources, recent efforts were directed towards the synthesis of renewable monomers and polymers, either for the substitution of petroleum‐based resources or for the design of novel polymers. Not only the use of biomass, but also the development of sustainable chemical approaches is a crucial aspect for the production of sustainable materials. This review discusses the recent examples of chemical modifications and polymerizations of abundant biomass resources with a clear focus on the sustainability of the described processes. Topics such as synthetic methodology, catalysis, and development of new solvent systems or greener alternative reagents are addressed. The chemistry of vegetable oil derivatives, terpenes, lignin, carbohydrates, and sugar‐based platform chemicals was selected to highlight the trends in the active field of a sustainable use of renewable resources. 相似文献