全文获取类型
收费全文 | 269篇 |
免费 | 7篇 |
国内免费 | 1篇 |
专业分类
化学 | 196篇 |
晶体学 | 1篇 |
力学 | 5篇 |
数学 | 45篇 |
物理学 | 30篇 |
出版年
2023年 | 2篇 |
2018年 | 5篇 |
2017年 | 4篇 |
2016年 | 4篇 |
2015年 | 3篇 |
2013年 | 7篇 |
2012年 | 12篇 |
2011年 | 14篇 |
2010年 | 7篇 |
2009年 | 5篇 |
2008年 | 15篇 |
2007年 | 16篇 |
2006年 | 15篇 |
2005年 | 16篇 |
2004年 | 10篇 |
2003年 | 7篇 |
2002年 | 5篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 4篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1978年 | 5篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1974年 | 8篇 |
1967年 | 7篇 |
1966年 | 9篇 |
1916年 | 2篇 |
1912年 | 3篇 |
1902年 | 3篇 |
1901年 | 3篇 |
1897年 | 2篇 |
1896年 | 2篇 |
1883年 | 1篇 |
1882年 | 2篇 |
1870年 | 1篇 |
排序方式: 共有277条查询结果,搜索用时 15 毫秒
31.
Bruijnincx PC Buurmans IL Huang Y Juhász G Viciano-Chumillas M Quesada M Reedijk J Lutz M Spek AL Münck E Bominaar EL Klein Gebbink RJ 《Inorganic chemistry》2011,50(19):9243-9255
The newly synthesized dinuclear complex [Fe(III)(2)(μ-OH)(2)(bik)(4)](NO(3))(4) (1) (bik, bis(1-methylimidazol-2-yl)ketone) shows rather short Fe···Fe (3.0723(6) ?) and Fe-O distances (1.941(2)/1.949(2) ?) compared to other unsupported Fe(III)(2)(μ-OH)(2) complexes. The bridging hydroxide groups of 1 are strongly hydrogen-bonded to a nitrate anion. The (57)Fe isomer shift (δ = 0.45 mm s(-1)) and quadrupole splitting (ΔE(Q) = 0.26 mm s(-1)) obtained from Mo?ssbauer spectroscopy are consistent with the presence of two identical high-spin iron(III) sites. Variable-temperature magnetic susceptibility studies revealed antiferromagnetic exchange (J = 35.9 cm(-1) and H = JS(1)·S(2)) of the metal ions. The optimized DFT geometry of the cation of 1 in the gas phase agrees well with the crystal structure, but both the Fe···Fe and Fe-OH distances are overestimated (3.281 and 2.034 ?, respectively). The agreement in these parameters improves dramatically (3.074 and 1.966 ?) when the hydrogen-bonded nitrate groups are included, reducing the value calculated for J by 35%. Spontaneous reduction of 1 was observed in methanol, yielding a blue [Fe(II)(bik)(3)](2+) species. Variable-temperature magnetic susceptibility measurements of [Fe(II)(bik)(3)](OTf)(2) (2) revealed spin-crossover behavior. Thermal hysteresis was observed with 2, due to a loss of cocrystallized solvent molecules, as monitored by thermogravimetric analysis. The hysteresis disappears once the solvent is fully depleted by thermal cycling. [Fe(II)(bik)(3)](OTf)(2) (2) catalyzes the oxidation of alkanes with t-BuOOH. High selectivity for tertiary C-H bond oxidation was observed with adamantane (3°/2° value of 29.6); low alcohol/ketone ratios in cyclohexane and ethylbenzene oxidation, a strong dependence of total turnover number on the presence of O(2), and a low retention of configuration in cis-1,2-dimethylcyclohexane oxidation were observed. Stereoselective oxidation of olefins with dihydrogen peroxide yielding epoxides was observed under both limiting oxidant and substrate conditions. 相似文献
32.
Julien Mesnager Emile Kuntz Catherine Pinel 《Journal of organometallic chemistry》2009,694(16):2513-799
In order to study the performance of organometallic complexes in the telomerization of butadiene with methanol in aqueous medium, we synthesized and characterised hydrosoluble palladium complexes. [(π-allyl)Pd(TPPTS)2]+Cl− complex exhibited strong stability as no degradation was observed after storage at room temperature under air atmosphere for weeks. TON’s up to 36 000 were achieved at 50 °C. 相似文献
33.
Anusree Mukherjee Marlène Martinho Dr. Emile L. Bominaar Dr. Eckard Münck Prof. Dr. Lawrence Que Jr. Prof. Dr. 《Angewandte Chemie (International ed. in English)》2009,48(10):1780-1783
Picky ferryl : The complex [Fe(Tp)(BF)] (Tp=hydrotris(3,5‐diphenylpyrazolyl)borate; BF=benzoylformate) reacts with O2 to generate an oxidant (see picture; O red, pink; Fe yellow; N blue; C gray; H white) that oxidizes added hydrocarbons shape‐selectively. Discrimination derives from a cleft formed by two phenyl groups of the Tp ligand, favoring oblate spheroidal substrates.
34.
Grotenbreg GM Kronemeijer M Timmer MS El Oualid F van Well RM Verdoes M Spalburg E van Hooft PA de Neeling AJ Noort D van Boom JH van der Marel GA Overkleeft HS Overhand M 《The Journal of organic chemistry》2004,69(23):7851-7859
A practical gram-scale and high-yielding synthesis of the antimicrobial peptide gramicidin S is presented. An Fmoc-based solid-phase peptide synthesis protocol is employed for the generation of the linear decapeptide precursor, which is cyclized in solution to afford the target compound. The versatility of our method is demonstrated by the construction of eight gramicidin S analogues (15a-h) having nonproteinogenic sugar amino acid residues (4-7) incorporated in the turn regions. 相似文献
35.
S Shah S Lee JY Verkhoturov S Tuleuova N Schweikert EA Ramanculov E Revzin A 《Langmuir : the ACS journal of surfaces and colloids》2008,24(13):6837-6844
This paper describes a novel approach of controlling cell-surface interactions through an electrochemical "switching" of biointerfacial properties of optically transparent microelectrodes. The indium tin oxide (ITO) microelectrodes, fabricated on glass substrates, were modified with poly(ethylene glycol) (PEG) silane to make glass and ITO regions resistant to protein and cell adhesion. Cyclic voltammetry, with potassium ferricyanide serving as a redox reporter molecule, was used to monitor electron transfer across the electrolyte-ITO interface. PEG silane modification of ITO correlated with diminished electron transfer, judged by the disappearance of ferricyanide redox activity. Importantly, application of reductive potential (-1.4 V vs Ag/AgCl reference) corresponded with reappearance of typical ferricyanide redox peaks, thus pointing to desorption of an insulating PEG silane layer. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) characterization of the silanized ITO surfaces after electrical stimulation indicated complete removal of the silane layer. Significantly, electrical stimulation allowed to "switch" chosen electrodes from nonfouling to protein-adhesive while leaving other ITO and glass regions protected by a nonfouling PEG silane layer. The spatial and temporal control of biointerfacial properties afforded by our approach was utilized to micropattern proteins and cells and to construct micropatterned co-cultures. In the future, control of the biointerfacial properties afforded by this novel approach may allow the organization of multiple cell types into precise geometric configurations in order to create better in vitro mimics of cellular complexity of the native tissues. 相似文献
36.
The essential oils obtained by hydro distillation of the aerial parts of Pituranthos scoparius were collected from different regions of Algeria and gave various yields ranging from 0.6 up to 2.8% (v/w). These samples were analyzed by GC and GC-MS showing the occurrence of monoterpene hydrocarbons and some oxygenated compounds. The major components were alpha-pinene (4.4-35.8%), limonene (0.8-66.5%), bornyl acetate (tr-9.6%), myristicin (tr-31.1) and dill apiole (0.4-47.3%). The aerial parts of P. scoparius could be either very rich or very poor in limonene, myristicin or dill apiole. Cluster analysis shows differences in essential oil compositions of samples coming from the different area collected. 相似文献
37.
It is well known that red blood cell scattering has an impact on whole blood oximetry as well as in vivo retinal oxygen saturation measurements. The goal of this study was to quantify the impact of small angle forward scatter on whole blood oximetry for scattering angles found in retinal oximetry light paths. Transmittance spectra of whole blood were measured in two different experimental setups: one that included small angle scatter in the transmitted signal and one that measured the transmitted signal only, at absorbance path lengths of 25, 50, 100, 250 and 500 μm. Oxygen saturation was determined by multiple linear regression in the 520-600 nm wavelength range and compared between path lengths and experimental setups. Mean calculated oxygen saturation differences between setups were greater than 10% at every absorbance path length. The deviations to the Beer-Lambert absorbance model had different spectral dependences between experimental setups, with the highest deviations found in the 520-540 nm range when scatter was added to the transmitted signal. These results are consistent with other models of forward scatter that predict different spectral dependences of the red blood cell scattering cross-section and haemoglobin extinction coefficients in this wavelength range. 相似文献
38.
Consola S Blanzat M Perez E Garrigues JC Bordat P Rico-Lattes I 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(11):3039-3047
A new kind of catanionic assembly was developed that associates a sugar-based surfactant with a non-steroidal anti-inflammatory drug (NSAID). Three different assemblies using indomethacin, ibuprofen and ketoprofen as NSAIDs were easily obtained in water by an acid-base reaction. These assemblies formed new amphiphilic entities because of electrostatic and hydrophobic effects in water and led to the spontaneous formation of vesicles. These catanionic vesicles were then tested as potential NSAID delivery systems for dermatological application. The anti-inflammatory activity was evaluated in vivo, and this study clearly showed an improved therapeutic effect for NSAIDs that were formulated as catanionic vesicles. These vesicles ensured a slower diffusion of the NSAID through the skin. This release probably increased the time of retention of the NSAID in the targeted strata of the skin. Thus, the present study suggests that this catanionic bioactive formulation could be a promising dermal delivery system for NSAIDs in the course of skin inflammation treatment. 相似文献
39.
Bendjaballah S Kahlal S Costuas K Bévillon E Saillard JY 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(7):2048-2065
DFT calculations with full geometry optimization have been carried out on a series of real and hypothetical compounds of the type [CpM(C8H6)], [(CO)3M(C8H6)], [M(C8H6)2], [(CpM)2(C8H6)], [[(CO)3M]2(C8H6)], and [M2(C8H6)2] (M = transition metal). The bonding in all the currently known compounds is rationalized, as well as in the (so far) hypothetical stable complexes. Depending on the electron count and the nature of the metal(s), eta2 (predicted), eta3, eta5, eta8, or intermediate coordination modes can be adopted. In the case of the mononuclear species, the most favored closed-shell electron counts are 18 and 16 metal valence electrons (MVE). In the case of the dinuclear species, an electron count of 34 MVEs is most favored. However, other electron counts can be stabilized, especially in the case of dinuclear complexes. Coordinated pentalene should most often be considered as formally being a dianion, but sometimes as a neutral ligand. In the former case it can behave as an aromatic species made of two equivalent fused rings, as a C5 aromatic ring connected to an allylic anion, or even as two allylic anions bridged by a C7=C8 double bond. In the latter case, it can behave as a bond-alternating cyclic polyene or as a C5 aromatic ring connected to an allylic cation. 相似文献
40.