全文获取类型
收费全文 | 904篇 |
免费 | 44篇 |
国内免费 | 1篇 |
专业分类
化学 | 782篇 |
晶体学 | 9篇 |
力学 | 3篇 |
数学 | 55篇 |
物理学 | 100篇 |
出版年
2023年 | 11篇 |
2022年 | 32篇 |
2021年 | 41篇 |
2020年 | 28篇 |
2019年 | 36篇 |
2018年 | 16篇 |
2017年 | 28篇 |
2016年 | 38篇 |
2015年 | 32篇 |
2014年 | 43篇 |
2013年 | 48篇 |
2012年 | 81篇 |
2011年 | 86篇 |
2010年 | 38篇 |
2009年 | 35篇 |
2008年 | 49篇 |
2007年 | 63篇 |
2006年 | 51篇 |
2005年 | 44篇 |
2004年 | 23篇 |
2003年 | 24篇 |
2002年 | 29篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 6篇 |
1998年 | 7篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 5篇 |
1993年 | 3篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1988年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1966年 | 1篇 |
1965年 | 2篇 |
1964年 | 1篇 |
1963年 | 1篇 |
1943年 | 1篇 |
1933年 | 1篇 |
1930年 | 2篇 |
1924年 | 1篇 |
1874年 | 1篇 |
1863年 | 1篇 |
排序方式: 共有949条查询结果,搜索用时 31 毫秒
11.
H. Pfaff 《Czechoslovak Journal of Physics》1995,45(7-8):673-679
The development of a Ring Imaging CHerenkov (RICH) detector working in an environment of strong hadronic background is needed for the High Acceptance Di-Electron Spectrometer (HADES). To get information about the charged particle background situation, a CERN RICH prototype with solid (CsI) photocathode was tested in a 1×A GeV U+Pb reaction at GSI. Also the quantum efficiency of the CsI photocathode was determined to be 10% at 175 nm.Presented at the International School-Workshop Relativistic Heavy-Ion Physics, Prague (Czech Republic), 19–23 September 1994.For the HADES Collaboration (IOP Bratislava, Univ. Clermont-Ferrand, GSI Darmstadt, Univ. Frankfurt, Univ. Gießen, Univ. Kraków, Univ. Milano, ITEP Moscow, LPI Moscow, MEPI Moscow, TU München, Univ. Nikosia, NPI e, Univ. Valencia).We would like to thank F. Piuz for providing the detector and A. Braem for the production of the CsI photocathode. We are also grateful to the accelerator crew at GSI for the stable beam and the Gießen crew W. Döring, A. Rühl and J. Schneider for support.This work was supported in part by BMFT under contract No. 06 GI 475 I(3) and by GSI. 相似文献
12.
13.
Carolina M Escobar-Llanos David Díaz Guillermo Mendoza-Díaz 《Journal of inclusion phenomena and macrocyclic chemistry》1998,31(4):333-349
The formation of inclusion complexes of -, -, hydroxypropyl-- (HP--) and -cyclodextrins with phenylbutazone and oxyphenbutazone has been studied in aqueous buffer solution (pH 7.5 and 0.1 mol dm-3 NaCl), dimethylsulfoxide, and 25, 50 and 75% dimethylsulfoxide/water mixtures. These complexation reactions have been followed by UV electronic absorption spectroscopy. In addition, 1D and 2D 1H NMR spectra were recorded to obtain structural information about the inclusion complexes formed in solution; 136 binding constant values were determined at five different temperatures (288, 293, 298, 303 and 310 K) from the electronic absorption data and, from these Hbinding and Sbinding values were obtained. At the studied cyclodextrin and guest concentration ranges, 1 : 1 inclusion complexes were detected. Only in three cases were 1 : 2 complexes detected, those of phenylbutazone and oxyphenbutazone with -cyclodextrin in aqueous, and oxyphenbutazone with hydroxypropyl--cyclodextrin in 75% dimethylsulfoxide/water solutions. 相似文献
14.
Carolina Menna Natalia Calonghi Lanfranco Masotti Paolo Neyroz 《Journal of fluorescence》1993,3(1):33-43
This report describes a method to conjugate lucifer yellow to the external surface of liposomes. The heterobifunctional cross-linking reagentN-succinimidyl 3-(2-pyridyldithio)propionate has been used to activate DMPE molecules. The DMPE-dithiopyridine product has been mixed with DMPC to prepare liposome vesicles. These have been reduced by DTT and finally reacted with lucifer yellow-iodoacetamide to produce the fluorescence-labeled vesicles. The quenching of their fluorescence intensity by Kl is consistent with fully exposed fluorophores. The decay of the fluorescence intensity of the lipid-bound lucifer yellow is biexponential (1=7.9 ns; 2=1.1 ns), with a relative yield of 0.16. When the fluorescent liposomes are mixed with cells, the lucifer yellow-DMPE derivative is transferred. Boar spermatozoa and peripheral human blood lymphocytes have been used as cellular models. The extent of incorporation is dependent on the incubation time and temperature. At 36°C, lucifer yellow fluorescence appears in the spermatozoa cells after 10 min of incubation and reaches its maximum at about 60 min. The fluorescent phospholipid derivative seems to incorporate specifically into membrane structures. The highest labeling ratio is observed with integer, scarcely motile, spermatozoa. A poorer labeling yield (15%) is found with lymphocytes. Interestingly, photobleaching due to epiillumination of the labeled cells is apparently negligible and cells are clearly visible after irradiation times ranging from several minutes to few hours.A preliminary account of this work was presented at the Quarto Simposio su Biotecnologie Biochimiche, Capri, 28–30 June 1992. 相似文献
15.
Rigol C Olea-Azar C Mendizábal F Otero L Gambino D González M Cerecetto H 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(13-14):2933-2938
Cyclic voltammetry and electron spin resonance (ESR) techniques were used in the investigation of several potential antiprotozoal thiosemicarbazones nitrofurane derivatives. A self-protonation process involving the protonation of the nitro group due to the presence of an acidic proton in the thiosemicarbazone moiety was observed in the first step of a CEE(rev) reduction mechanism of these derivatives. ESR spectra of the free radicals obtained by electrolytic reduction were characterized and analyzed. AM1 methodology was used to obtain the optimized geometries and UB3LYP calculations were performed to obtain the theoretical hyperfine coupling constants. The theoretical study exhibited an unusual assignment of the spin densities showing a free radical centered in the thiosemicarbazone moiety rather than the nitro which are in agreement with the experimental hyperfine pattern. 相似文献
16.
OXYGEN DIFFUSION THROUGH HORSERADISH PEROXIDASE 总被引:4,自引:0,他引:4
Juan E. Brunet Carolina Jullian David M. Jameson 《Photochemistry and photobiology》1990,51(4):487-489
The quenching by molecular oxygen of the fluorescence from a protoporphyrin IX adduct of horseradish peroxidase has been investigated using both intensity and time-resolved techniques. The bimolecular quenching rate constant determined for this process, as evaluated by the conventional Stern-Volmer analysis, was 2 x 10(8) M-1 s-1, among the lowest observed for protein systems. This result suggests that the heme binding site in horseradish peroxidase is relatively inaccessible to oxygen, which may account for the observation of room temperature phosphorescence in aerated solutions from enzymatically created triplet states. 相似文献
17.
M. Carolina Navarro Silvina Pagola Raúl E. Carbonio 《Journal of solid state chemistry》2005,178(3):847-854
The crystal structure of Nd[Fe(CN)6]·4H2O has been refined by Rietveld analysis using high resolution synchrotron powder X-ray diffraction data. It belonged to the orthorhombic crystal system, Cmcm space group, with cell parameters: , and . The change in space group from P63/m which is observed in the pentahydrates (LnFe(CN)6·5H2O) to Cmcm in the tetrahydrates has been analyzed to be a consequence of the change in 9-fold coordination of Nd3+ in the pentahydrates to 8-fold coordination in the tetrahydrates, which changes the Nd3+ environment from tricapped trigonal prism to a distorted tricapped trigonal prism or square antiprism. Its decomposition process in air to produce NdFeO3 has been followed by thermogravimetric and differential thermal analysis, IR spectroscopy and laboratory powder XRD. We found that it is possible to synthesize crystalline NdFeO3 at temperatures as low as 380 °C and refine the structure of single phase crystalline NdFeO3 synthesized by this method at 600 °C. 相似文献
18.
De la Fuente JR Jullian C Saitz C Neira V Poblete O Sobarzo-Sánchez E 《The Journal of organic chemistry》2005,70(22):8712-8716
[reaction: see text] Photoreduction of oxoisoaporphine dyes occurs via a stepwise mechanism of electron-proton-electron transfer that leads to the N-hydrogen oxoisoaporphine anion. When triethylamine, TEA, was used as the electron donor in anaerobic conditions, 1-diethylaminobutadiene, DEAB, was one of the oxidation products of TEA, among diethylamine and acetaldehyde. DEAB was identified by (1)H NMR and GC-MS experiments by comparison with the authentic 1-diethylaminobutadiene. This is the first report of a butadienyl derivative formed in the dye-sensitized photooxidation of TEA. In addition, isotopic exchange experiments with TEA-d(15) and D(2)O show that the hydrogens at carbon-2 and carbon-4 of the butadienyl moiety are exchangeable. The observed isotopic exchange pattern could be explained by the head-to-tail coupling of an N,N-diethylvinylamine intermediate that exchanges hydrogens at the C-beta via the enammonium ion. 相似文献
19.
Erik G.P. da Silva Ana Carolina do N. Santos Antnio C.S. Costa Dalva M. da N. Fortunato Ndia M. Jos Maria G.A. Korn Walter N.L. dos Santos Srgio L.C. Ferreira 《Microchemical Journal》2006,82(2):159-162
In the present work, a slurry sampling flame atomic absorption spectrometric method to determine directly manganese and zinc in powdered chocolate samples is proposed. The optimization step was performed using univariate methodology involving the following factors: nature and concentration of the acid solution, sonication time, and particle size. The established conditions led to the use of a sample mass of 150 mg, 2.0 mol L− 1 nitric acid solution, sonication time of 15 min, and a slurry volume of 50 mL. This method allows the determination of manganese and zinc with detection limit of 52 and 61 ng g− 1, respectively, and a precision expressed as relative standard deviation (RSD) of 2.6% and 3.2% (both, n = 10) for contents of manganese and zinc of 52.4 and 100.0 μg g− 1, respectively. The proposed method was applied for determination of manganese and zinc in five powdered chocolate samples. In these, the manganese content varied from 42.8 to 52.7 and from 88.6 to 102.4 μg g− 1 of zinc. The analytical results were compared with the results obtained by analysis of these samples after digestion using open vessel and acid bomb digestion procedures and determination using FS-FAAS. The statistical comparison by t-test (95% confidence level) showed no significant difference between these results. 相似文献
20.
Glass Formation and Properties of Chalcogenide Systems. XIII. On the Compounds Na6Ge2S6 · 4 CH3OH and Na6Ge2Se6 · 4 CH3OH The glasses Ge2S3 and Ge2Se3 are soluble in solutions of Na2S or Na2Se in CH3OH forming Na6Ge2S6 · 4 CH3OH and Na6Ge2Se6 · 4 CH3OH. On heating the CH3OH-free substances are formed. From the i.r. and Raman spectra can de seen that the structure of the ions Ge2S, Ge2Se, P2S64?, and of Si2Cl6 is of the same type. The formation of the compounds can be regarded as a chemical proof for the existence of [Ge2S6] and [Ge2Se6] units as structural groups in the glasses Ge2S3 and Ge2Se3. 相似文献