全文获取类型
收费全文 | 473篇 |
免费 | 7篇 |
国内免费 | 1篇 |
专业分类
化学 | 288篇 |
晶体学 | 23篇 |
力学 | 17篇 |
数学 | 32篇 |
物理学 | 121篇 |
出版年
2022年 | 3篇 |
2021年 | 19篇 |
2020年 | 5篇 |
2019年 | 6篇 |
2018年 | 2篇 |
2017年 | 4篇 |
2016年 | 6篇 |
2015年 | 4篇 |
2014年 | 12篇 |
2013年 | 12篇 |
2012年 | 16篇 |
2011年 | 25篇 |
2010年 | 10篇 |
2009年 | 21篇 |
2008年 | 40篇 |
2007年 | 32篇 |
2006年 | 37篇 |
2005年 | 20篇 |
2004年 | 21篇 |
2003年 | 16篇 |
2002年 | 9篇 |
2001年 | 10篇 |
2000年 | 6篇 |
1999年 | 7篇 |
1998年 | 4篇 |
1996年 | 11篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 8篇 |
1991年 | 5篇 |
1990年 | 11篇 |
1989年 | 6篇 |
1988年 | 12篇 |
1987年 | 8篇 |
1985年 | 5篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1975年 | 5篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1970年 | 2篇 |
1906年 | 1篇 |
1898年 | 1篇 |
1888年 | 4篇 |
排序方式: 共有481条查询结果,搜索用时 15 毫秒
91.
Leone SR 《The journal of physical chemistry. A》2008,112(39):9169-9176
92.
Francesca Scazzocchio Stefania Garzoli Cinzia Conti Claudia Leone Clio Renaioli Federico Pepi 《Natural product research》2016,30(17):1909-1918
Because of the emergence of multi-drug resistance bacteria and fungi, alternatives to conventional antimicrobial therapy are needed. This study aims to evaluate in vitro the antimicrobial activity of: Mirtus communis, Coriandrum sativum, Pelargonium capitatum, Cuminum cyminum, Ocimum basilicum, Citrus aurantium amara, Cymbopogon. winterianus, Cymbopogon martini, Salvia sclarea, Melaleuca alternifolia and Mentha suaveolens essential oils on bacteria and fungi, in relation to their chemical composition. The potential interaction of M. alternifolia (TTO), C. sativum (CDO) and M. suaveolens (EOMS) essential oils when used in combination with gentamicin and fluconazole has been evaluated. The results obtained showed a synergic effect on some bacteria and fungi, with FICI values ≤5. The cytotoxicity of TTO, CDO and EOMS was investigated towards HeLa cells. Only EOMS did not result cytotoxic at the active concentrations on micro-organisms. Further studies are necessary to obtain optimal ratios and dosing regimens for higher therapeutic efficacy and to decrease toxicological profiles. 相似文献
93.
Goulay F Osborn DL Taatjes CA Zou P Meloni G Leone SR 《Physical chemistry chemical physics : PCCP》2007,9(31):4291-4300
The reactions of the ethynyl radical (C(2)H) with propyne and allene are studied at room temperature using an apparatus that combines the tunability of the vacuum ultraviolet radiation of the Advanced Light Source at Lawrence Berkeley National Laboratory with time-resolved mass spectrometry. The C(2)H radical is prepared by 193-nm photolysis of CF(3)CCH and the mass spectrum of the reacting mixture is monitored in time using synchrotron-photoionization with a dual-sector mass spectrometer. Analysis using photoionization efficiency curves allows the isomer-specific detection of individual polyynes of chemical formula C(5)H(4) produced by both reactions. The product branching ratios are estimated for each isomer. The reaction of propyne with ethynyl gives 50-70% diacetylene (H-C[triple bond]C-C[triple bond]C-H) and 50-30% C(5)H(4), with a C(5)H(4)-isomer distribution of 15-20% ethynylallene (CH(2)=C=CH-C[triple bond]CH) and 85-80% methyldiacetylene (CH(3)-C[triple bond]C-C[triple bond]CH). The reaction of allene with ethynyl gives 35-45% ethynylallene, 20-25% methyldiacetylene and 45-30% 1,4-pentadiyne (HC[triple bond]C-CH(2)-C[triple bond]CH). Diacetylene is most likely not produced by this reaction; an upper limit of 30% on the branching fraction to diacetylene can be derived from the present experiment. The mechanisms of polyynes formation by these reactions as well as the implications for Titan's atmospheric chemistry are discussed. 相似文献
94.
A cyclen derivative bearing a ferrocenyl arm (L) and a series of its ZnII complexes [ZnL(OH2)][ClO4]2 (C1), [ZnL(OH)][ClO4] (C2), and [ZnL(Cl)][ClO4].CH3CN (C3) (cyclen = 1,4,7,10-tetraazacyclododecane, L = 1-(ferrocenemethyl)-1,4,7,10-tetraazacyclododecane) have been prepared and characterized spectroscopically. An X-ray structure determination confirmed the formation of complex C1 and revealed that the coordinated water participates in hydrogen bonding with the perchlorate counter ions. The pKa value for deprotonation of the water molecule determined by potentiometric titration was found to be 7.36 +/- 0.09 at 25 degrees C and I = 0.1 (KNO3). The possibility of using complex C1 as a potential sensor for thymine derivatives in aqueous solution has been examined. Shifts in the 1H and 13C NMR resonances showed the binding occurred with thymine (T) and two thymine derivatives, thymidine (dT) and thymidine 5'-monophosphate (TMP2-). Significant shifts of the nuC=O and nuC=C vibrations of the thymine derivatives were also observed via IR spectroscopy upon complexation with the receptor. The thymine adduct, [ZnL(thymine anion)][ClO4].2H2O (C4), has been crystallized and characterized. The X-ray structure of C4 confirmed the thymine binding to the receptor, and the short Zn-N(thymine) distance of 1.975(5) A indicated clearly that the ferrocenyl arm does not affect the complexation of the DNA base. In contrast to the large spectral changes, electrochemical studies showed a small shift of the reversible potential of the redox couple Fc+/Fc (Fc = ferrocene) and subtle changes in voltammetry upon the addition of an excess of dT, TMP2-, and guanine (dG) at physiological pH, indicating the level of interaction is similar in both Fc and Fc+ forms. 相似文献
95.
Lisa Russelli Francesco De Rose Loredana Leone Sybille Reder Markus Schwaiger Calogero DAlessandria Lorenzo Tei 《Molecules (Basel, Switzerland)》2021,26(19)
In this work, we designed, developed, characterized, and investigated a new chelator and its bifunctional derivative for 89Zr labeling and PET-imaging. In a preliminary study, we synthesized two hexadentate chelators named AAZTHAS and AAZTHAG, based on the seven-membered heterocycle AMPED (6-amino-6-methylperhydro-1,4-diazepine) with the aim to increase the rigidity of the 89Zr complex by using N-methyl-N-(hydroxy)succinamide or N-methyl-N-(hydroxy)glutaramide pendant arms attached to the cyclic structure. N-methylhydroxamate groups are the donor groups chosen to efficiently coordinate 89Zr. After in vitro stability tests, we selected the chelator with longer arms, AAZTHAG, as the best complexing agent for 89Zr presenting a stability of 86.4 ± 5.5% in human serum (HS) for at least 72 h. Small animal PET/CT static scans acquired at different time points (up to 24 h) and ex vivo organ distribution studies were then carried out in healthy nude mice (n = 3) to investigate the stability and biodistribution in vivo of this new 89Zr-based complex. High stability in vivo, with low accumulation of free 89Zr in bones and kidneys, was measured. Furthermore, an activated ester functionalized version of AAZTHAG was synthesized to allow the conjugation with biomolecules such as antibodies. The bifunctional chelator was then conjugated to the human anti-HER2 monoclonal antibody Trastuzumab (Tz) as a proof of principle test of conjugation to biologically active molecules. The final 89Zr labeled compound was characterized via radio-HPLC and SDS-PAGE followed by autoradiography, and its stability in different solutions was assessed for at least 4 days. 相似文献
96.
97.
Glen B. Deacon Pauline Pearson Brian W. Skelton Leone Spiccia Allan H. White 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(12):m537-m539
The syntheses and crystal structure determinations of a pair of `sawhorse' dimers are reported, viz. [Ru2(C6H5CO2)2(C5H5N)2(CO)4] [a new polymorph, cf. Kepert, Deacon, Spiccia, Fallon, Skelton & White (2000). J. Chem. Soc. Dalton Trans. pp. 2867–2874] and [Ru2(CF3CO2)2(C5H5N)2(CO)4]. The Ru⋯Ru distances are 2.6724 (2) and 2.7122 (5) Å, respectively. 相似文献
98.
99.
Adam J. Trevitt Fabien Goulay Giovanni Meloni David L. Osborn Craig A. Taatjes Stephen R. Leone 《International journal of mass spectrometry》2009,280(1-3):113
Product detection studies of CN reactions with ethene and propene are conducted at room temperature (4 Torr, 533.3 Pa) using multiplexed time-resolved mass spectrometry with tunable synchrotron photoionization. Photoionization efficiency curves, i.e., the ion signal as a function of photon energy, are used to determine the products and distinguish isomers. Both reactions proceed predominantly via CN addition to the π orbital of the olefin. For CN + ethene, cyanoethene (C2H3CN) is detected as the sole product in agreement with recent studies on this reaction. Multiple products are identified for the CN + propene reaction with 75(±15)% of the detected products in the form of cyanoethene from a CH3 elimination channel and 25(±15)% forming different isomers of C4H5N via H elimination. The C4H5N comprises 57(±15)% 1-cyanopropene, 43(±15)% 2-cyanopropene and <15% 3-cyanopropene. No evidence of direct H abstraction or indirect HCN formation is detected for either reaction. The results have relevance to the molecular weight growth chemistry on Saturn's largest moon Titan, where the formation of small unsaturated nitriles are proposed to be key steps in the early chemical stages of haze formation. 相似文献
100.
Elastic light scattering is reported using monochromatic vacuum-ultraviolet radiation to study free, spherical silica nanoparticles prepared by approaches from colloidal chemistry, with diameters between 100 and 240 nm. The colloidal nanoparticles of defined size are transferred from an aqueous solution into the gas phase using a particle beam experiment. After focusing of the particle beam by an aerodynamic lens, the scattered light from monochromatic synchrotron radiation is measured. Angle-resolved elastically scattered light is detected, showing a strong forward-scattering component. Additional evidence for the detection of elastically scattered light comes from plotting the scattered light intensity as a function of the dimensionless parameter qR, where q is the magnitude of the scattering wave vector and R is the particle radius. This yields different power-law regimes that are assigned to scattering from the surface and the bulk of the nanoparticles. Furthermore, there is evidence for modulations in the scattered light intensity as a function of scattering angle, which is clearly distinguished from the forward-scattering component. The experimental results are compared to Mie scattering simulations for isolated particles, yielding general agreement with the experimental results. Deviations from Mie simulations are observed for samples consisting of significant amounts of aggregates. The present results indicate that the optical properties of free nanoparticles are sensitively probed by vacuum-ultraviolet radiation. 相似文献