全文获取类型
收费全文 | 2726篇 |
免费 | 129篇 |
国内免费 | 15篇 |
专业分类
化学 | 1978篇 |
晶体学 | 13篇 |
力学 | 80篇 |
数学 | 407篇 |
物理学 | 392篇 |
出版年
2023年 | 24篇 |
2022年 | 50篇 |
2021年 | 61篇 |
2020年 | 69篇 |
2019年 | 56篇 |
2018年 | 66篇 |
2017年 | 59篇 |
2016年 | 111篇 |
2015年 | 97篇 |
2014年 | 117篇 |
2013年 | 203篇 |
2012年 | 226篇 |
2011年 | 223篇 |
2010年 | 141篇 |
2009年 | 116篇 |
2008年 | 182篇 |
2007年 | 175篇 |
2006年 | 127篇 |
2005年 | 120篇 |
2004年 | 132篇 |
2003年 | 88篇 |
2002年 | 68篇 |
2001年 | 27篇 |
2000年 | 25篇 |
1999年 | 22篇 |
1998年 | 13篇 |
1997年 | 9篇 |
1996年 | 22篇 |
1995年 | 11篇 |
1994年 | 13篇 |
1993年 | 15篇 |
1992年 | 15篇 |
1991年 | 10篇 |
1990年 | 14篇 |
1989年 | 12篇 |
1988年 | 8篇 |
1987年 | 15篇 |
1985年 | 11篇 |
1984年 | 14篇 |
1983年 | 5篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 12篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1975年 | 9篇 |
1973年 | 5篇 |
1971年 | 5篇 |
排序方式: 共有2870条查询结果,搜索用时 15 毫秒
41.
Silva Silvio S. Ribeiro JoÃo D. Felipe Maria G. A. Vitolo Michelle 《Applied biochemistry and biotechnology》1997,(1):557-564
Batch fermentations of sugar cane bagasse hemicellulosic hydrolysate treated for removing the inhibitors of the fermentation
were performed byCandida guilliermondii FTI20037 for xylitol production. The fermentative parameters agitation and aeration rate were studied aiming the maximization
of xylitol production from this agroindustrial residue. The maximal xylitol volumetric productivity (0.87 g/L h) and yield
(0.67 g/g) were attained at 400/min and 0.45 v.v.m. (KLa 27/h). According to the results, a suitable control of the oxygen input permitting the xylitol formation from sugar cane
bagasse hydrolysate is required for the development of an efficient fermentation process for large-scale applications. 相似文献
42.
Pedro A. Fernandes Elsa S. Henriques Vineet Pande Maria. J. Ramos Ana R. R. Maia André A. S. Almeida Bruno F. B. Silva Carla M. S. Ribeiro César F. B. Ribeiro David S. M. Ribeiro Diana A. P. Fonseca Eva M. S. Cunha Filipe R. N. C. Maia Joana A. A. Pereira João P. G. Pacheco Joaquim A. A. D. Ferreira Liliana R. C. Matos Manuel A. B. P. Pinto Maria C. S. Borges Paulo J. C. R. Magalhães Pedro F. R. D. Teixeira Pedro N. B. C. Veloso Ricarte J. F. Ferreira Sandro S. Gomes Tiago F. Barros Tiago S. J. T. Selão Virgínia M. M. C. Fernandes 《Theoretical chemistry accounts》2005,113(4):197-204
We present a series of new inhibitors of the association between nuclear factor kappa B (NF-B) and the corresponding B site in DNA. They were designed using the lead compound 15-deoxy-12,14 -prostaglandin J2 (PGJ2), which is a natural product with demonstrated inhibitory efficiency for this system. First, the binding mode of PGJ2 to NF-B was unraveled by GOLD docking calculation. Subsequently, substitutions were made to PGJ2 to optimize its association with NF-B. Care was taken not to strongly increase the reactivity of the new compounds, and to keep the overall shape, size and hydrophilicity of the lead compound, which should render them a similar bioavailability. Molecular mechanics calculations were performed to decide on the suitability of the substitutions, and to evaluate the energies of association with NF-B. Density functional theory calculations were performed also to study the overall reactivity of the substituted drugs towards NF-B. Important general conclusions were obtained, concerning the improvement of these natural inhibitors; namely, a set of rational methodologies were deduced to improve the association between the PGJ2 derivatives and NF-B, and their efficiency demonstrated by generating a set of substituted complexes, some of them with a very much increased affinity for NF-B, opening new doors to enlarge the therapeutic capabilities of this class of drugs. 相似文献
43.
A complex Diels-Alder reaction between a semi-cyclic diene with allylic silyloxy substituents and a bromo enone presented an unusual diastereoselectivity: attack of the diene occured on its more hindered face, and this reversal of selectivity was shown to be induced by the presence of a bromo substituent in the dienophile. 相似文献
44.
Using the electrochemical surface forces apparatus, we investigated adhesion (from pull-off measurements) between gold and mica as the potential of the gold surface was changed externally. Measurements were performed at different concentrations of KClO(4) in a potential window where the gold electrode is ideally polarizable. At applied potentials where the gold-mica interactions are repulsive, we obtain double layer forces that are predictable by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of colloid stability but deviate from the theory at short range. At applied potentials where the gold-mica interactions are attractive, we observed a very strong dependence of adhesion on the applied potential, a result that cannot be directly related to DLVO theory. We show, however, that an approach based on electrocapillary thermodynamics can be employed to model the potential dependence of adhesion seen in our measurements. This electrocapillary approach presents evidence of charging at the gold-mica interface and stresses the relation between the charge within and outside of the contact area. 相似文献
45.
Poriel C Ferrand Y le Maux P Raul-Berthelot J Simonneaux G 《Chemical communications (Cambridge, England)》2003,(9):1104-1105
Anodic oxidation of tetraspirobifluorene-manganese porphyrin lead to the coating of the working electrode by insoluble electroactive poly(9,9'-spirobifluorene-manganese porphyrin) films for which electrochemical behaviour and physicochemical properties are described; these polymeric materials are able to catalyze the heterogeneous epoxidation of styrene with iodobenzene diacetate and iodosylbenzene. 相似文献
46.
Anne Marie Larsonneur-Galibert Paule Castan Joël Jaud Gérald Bernardinelli 《Transition Metal Chemistry》1996,21(6):546-550
Summary The addition of NPm (diphenylaminodiphenylphosphinomethane) to CuI or the addition of KI to (NPm)2CuNO3 leads to the same P-bonded CuI complex, (NPm)2CuI, presenting a trigonal geometry around the Cu atom. The reaction of this new complex (or of its chloro analogue) with a CuII salt yields dinuclear species of general formula [(NPm)Cu(-X)2Cu(NPm)] (X = Cl or I). X-ray analysis of these complexes show that they are isostructural and retain the trigonal geometry around the metal atom. The Cu···Cu distances are 2.775(1)Å for X = Cl and 2.642(1) Å for X = I. The Cu-(-X)-Cu angle is more acute for the iodide [61.48(3)°] than for the chloride [74.17(8)°] complex. These values are discussed in terms of Cu···Cu interactions induced by the electron donor ability of X and the bulk of the phosphine L. 相似文献
47.
48.
Top layers of γ-Al2O3 composite membranes have been modified by the silane coupling technique using phenyltriethoxysilane for improving the separation factor of CO2 to N2. The separation efficiency of the modified membranes was strongly dependent upon the hydroxylation tendency of the support materials and the amount of the special functional group (i.e. phenyl radical) which was coupled onto a top layer. The separation factor through the TiO2 supported γ-Al2O3 membrane was found to be fairly enhanced by silane coupling, but in case of the -Al2O3 supported membrane was not. The CO2/N2 separation factor through the modified γ-Al2O3/TiO2 composite membrane is 1.7 at 90°C and ΔP = 2 × 105 Pa for the binary mixture containing 50 vol% CO2. The separation factor is proportional to the CO2 concentration in the gas mixture, and the modified membrane is stable up to 100°C. The main mechanism of the CO2 transport through the modified γ-Al2O3 layer is known to be a surface diffusion. 相似文献
49.
Puibasset J 《The Journal of chemical physics》2005,122(13):134710
The effect of confinement on phase behavior of simple fluids is still an area of intensive research. In between experiment and theory, molecular simulation is a powerful tool to study the effect of confinement in realistic porous materials, containing some disorder. Previous simulation works aiming at establishing the phase diagram of a confined Lennard-Jones-type fluid, concentrated on simple pore geometries (slits or cylinders). The development of the Gibbs ensemble Monte Carlo technique by Panagiotopoulos [Mol. Phys. 61, 813 (1987)], greatly favored the study of such simple geometries for two reasons. First, the technique is very efficient to calculate the phase diagram, since each run (at a given temperature) converges directly to an equilibrium between a gaslike and a liquidlike phase. Second, due to volume exchange procedure between the two phases, at least one invariant direction of space is required for applicability of this method, which is the case for slits or cylinders. Generally, the introduction of some disorder in such simple pores breaks the initial invariance in one of the space directions and prevents to work in the Gibbs ensemble. The simulation techniques for such disordered systems are numerous (grand canonical Monte Carlo, molecular dynamics, histogram reweighting, N-P-T+test method, Gibbs-Duhem integration procedure, etc.). However, the Gibbs ensemble technique, which gives directly the coexistence between phases, was never generalized to such systems. In this work, we focus on two weakly disordered pores for which a modified Gibbs ensemble Monte Carlo technique can be applied. One of the pores is geometrically undulated, whereas the second is cylindrical but presents a chemical variation which gives rise to a modulation of the wall potential. In the first case almost no change in the phase diagram is observed, whereas in the second strong modifications are reported. 相似文献
50.
Schäfer T Di Paolo RE Franco R Crespo JG 《Chemical communications (Cambridge, England)》2005,(20):2594-2596
We report on the molecular interactions between room-temperature ionic liquids (RTILs) and Nafion and PDMS membranes, proving that in contact with these polymers RTILs behave like electrolytes rather than solvents. 相似文献