全文获取类型
收费全文 | 1036篇 |
免费 | 197篇 |
国内免费 | 30篇 |
专业分类
化学 | 1178篇 |
晶体学 | 5篇 |
力学 | 18篇 |
综合类 | 1篇 |
数学 | 2篇 |
物理学 | 59篇 |
出版年
2023年 | 7篇 |
2022年 | 23篇 |
2021年 | 34篇 |
2020年 | 40篇 |
2019年 | 33篇 |
2018年 | 25篇 |
2017年 | 36篇 |
2016年 | 89篇 |
2015年 | 50篇 |
2014年 | 64篇 |
2013年 | 90篇 |
2012年 | 61篇 |
2011年 | 55篇 |
2010年 | 57篇 |
2009年 | 55篇 |
2008年 | 60篇 |
2007年 | 56篇 |
2006年 | 46篇 |
2005年 | 66篇 |
2004年 | 47篇 |
2003年 | 63篇 |
2002年 | 26篇 |
2001年 | 16篇 |
2000年 | 11篇 |
1999年 | 18篇 |
1998年 | 12篇 |
1997年 | 27篇 |
1996年 | 17篇 |
1995年 | 6篇 |
1994年 | 23篇 |
1993年 | 9篇 |
1992年 | 13篇 |
1991年 | 8篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有1263条查询结果,搜索用时 15 毫秒
11.
Crosslinked hyaluronan gels are used in various applications where their stability is a prerequisite. The sensitivity of such gels to hyaluronidase can be determined as an index of stability by several approaches: chromatography, electrophoresis, and viscometry. We describe here a test based on the colorimetric determination of the N-acetyl-d-glucosamine released by hyaluronidase in standardized conditions. The sensitivities to bovine testicular hyaluronidase of 11 different gels used to fill skin wrinkles (Restylane; Perlane; Juvéderm 18, 24, 24HV, 30, and 30HV; Surgiderm 18, 24XP, 30, and 30XP) were compared.The method was reproducible, easy to perform, not time-consuming and allowed us to demonstrate that the sensitivity to testicular hyaluronidase was dependent on the degree of crosslinking of the gels and also on their monophasic/biphasic nature. Under our conditions, Surgiderm 30, 24XP and 30XP were the most resistant gels.We propose to retain the hyaluronidase test to predict the in situ stability of a crosslinked gel used to fill skin wrinkles. 相似文献
12.
Composite membranes were prepared by (a) infiltrating NAFION with SiO2-P2O5-ZrO2 sol, and (b) recasting a film using NAFION solution containing SiO2-P2O5-ZrO2 sol. The membranes were characterized by Differential Thermal Analysis and ac-impedance spectroscopy as a function of relative humidity. The influences of the heat treatment (80°C–150°C) and cleaning on the electrical properties were investigated. The incorporation of SiO2-P2O5-ZrO2 gels into NAFION lead to improvements in its thermal stability and proton conductivity. 相似文献
13.
Controlled drug delivery remains a research focus for public health to enhance patient compliance, drug efficiency and reduce
the side effects of drugs. Pectin, an edible plant polysaccharide, has been shown to be useful for the construction of drug
delivery systems for specific drug delivery. Several pectin derived formulations have been developed in our laboratory and
tested in vitro, ex vivo, and in vivo for the ability to deliver bioactive substances for therapeutic purposes in the context of interactions with living tissues.
Pectin derivatives carrying primary amine groups were more mucoadhesive and have shown potential in nasal drug delivery and
other mucosal drug delivery. Pectin derivatives with highly esterified galacturonic acid residues are more hydrophobic and
able to sustain the release of incorporated fragrances for a prolonged duration. Less esterified pectin derivatives are able
to penetrate deeper into the skin and may be useful in aromatherapy formulations. Pectin, in combination with zein, a corn
protein, forms hydrogel beads. The bound zein restricts bead swelling and retains the porosity of the beads; the pectin networks
shield the zein from protease attack. The complex beads are ideal vehicles for colon-specific drug delivery. Studies presented
in this paper indicate the flexibility and possibility to tailor pectin macromolecules into a variety of drug delivery systems
to meet different clinical requirements.
Mention of trade names or commercial products in this article is solely for the purpose of providing specific information
and does not imply recommendation or endorsement by the US Department of Agriculture. 相似文献
14.
Barthez J.M. Molino F. Marignan J. Ayral A. Guizard C. Jullien R. 《Journal of Sol-Gel Science and Technology》1997,8(1-3):83-88
We present here an experimental and numerical study of the chemical and aggregative mechanisms for titanium alkoxide in a
reverse micellar medium. NMR experiments were done to study the first step of the sol-gel process: hydrolysis of titanium
isopropoxide. Light and X-ray scattering experiments were then conducted to characterize the clustering of aggregates and
aggregation kinetics. Fractal dimension, measured by U.S.A.X.S., varies with the hydrolysis ratio and the hydration of the
surfactant. This evolution was explained by polydispersity of the hydrolysis which depends on the surfactant concentration.
This hypothesis was tested through a numerical simulation of irreversible aggregation using a chemically limited aggregation
model. The hydrolyzed sites are distributed among the monomers by a random procedure governed by a polydispersity parameterp, varying from 0 to 1. The total number of hydrolyzed sites is governed by a parameterq belonging to the interval [0, 1]. Thep-q evolution of the fractal dimension coincides rather well with the experimental data in all the region of the two dimensional
phase space. 相似文献
15.
Stéphanie Ricol Etienne Vernaz Philippe Barboux 《Journal of Sol-Gel Science and Technology》1997,8(1-3):229-233
Gels have been synthesized in the SiO2-Na2O-ZrO2 system and calcined at various temperatures up to 700°C. They have been studied by infrared absorption spectroscopy. The position of the asymmetric stretching frequency of the SiO4 unit is used as a tracer of the homogeneity. It is shown that sodium increases the solubility of zirconium in the silica matrix as already observed in fused glasses. 相似文献
16.
Mikhail Vorob''ev 《Colloids and surfaces. B, Biointerfaces》2003,31(1-4):133-140
The role of aqueous media in the stabilization of globular proteins and formation of gels was studied by absorption millimeter spectroscopy. This method allowed to measure bound water, the fraction of water which had decreased rotational mobility owing to the presence of solute. Hydration data for globular proteins were compared with data obtained previously for low-weight molecules and groups. It was found that rotational mobility of water molecules in the hydration shells of various kinds of solutes (groups) decreased in the following order: water structure breaking compounds>polar groups>unfolded proteins>globular proteins>non-polar groups. Time courses of the storage modulus were determined for the chemical acidification by glucono-δ-lactone (GDL) of milk samples prepared from skimmed milk powder (SMP). Gelation of unheated milk was a monotonous process that started at pH 4.9. Heat-treated milk from SMP (16 and 14 g per 100 ml) acidified by GDL (3 g per 100 ml) at 43 °C gave non-monotonous kinetics of gelation with two phases corresponding to the mechanisms induced by denatured whey proteins at pH>5 and by casein–casein interactions at pH 4.8–4.9. For heat-treated milk, measurement of bound water gave two stages of decrease in water mobility. Additional hydration of SMP during acidification gave 0.15–0.2 g and 0.8 g bound H2O per gram of SMP for unheated and heat-treated milk, respectively. 相似文献
17.
Brett Ammundsen Gary R. Burns Ali Amran Stig E. Friberg 《Journal of Sol-Gel Science and Technology》1995,4(1):23-29
The effects of thermal treatment on composite materials prepared by the gelation of sols comprising large concentrations of metal oxide precursor salts have been investigated, in order to determine the compositional and thermal requirements for forming spinel magnesium manganates in such systems. The preparative technique has been found to give rise to derived gel materials in which the metal oxide phase, in the form of regular spherical particles, is dispersed throughout a continuous silica matrix. Silica-supported mixed magnesium and manganese spinel oxide phases were obtained for systems comprising at least 30 wt% metal nitrate after heating to temperatures between 700 and 850°C, but not without concomitant formation of Mn2O3 and modification of the silica network by magnesium. 相似文献
18.
19.
P. Favard J. P. Lechaire M. Maillard N. Favard P. Andreazza F. Lefaucheux M. C. Robert 《Colloid and polymer science》1992,270(6):584-589
Silica gel provides a useful medium for crystal growth; solution growth is confined to pores left free by the polymer during its development. All growth steps depend on the gel structure, which is not completely known for crystal growth conditions. Therefore, a three-dimensional (3-D) visualization has been performed for two TMOS aqueous gels, which are rather fragile: the quick-freeze, deep-etching, rotary-replication method has been applied for sample preparation. An original surface labeling technique has been used for surface recognition. The results concern the distribution of macropores that are responsible for crystal nucleation; micropores whose total volume is larger have not been visualized due to the limits of the method. These results are discussed in comparison with previous data performed by light scattering. 相似文献
20.
Phase transition of water restrained by curdlan suspension
annealed at a temperature from 20 to 110°C was investigated by differential
scanning calorimetry (DSC). The melting temperature of water restrained by
annealed curdlan discontinuously decreased at around 60°C, while the amount
of bound water calculated from enthalpy of melting increased at 60°C,
regardless of water content. Using a highly sensitive DSC, curdlan suspension
with various concentrations was studied. It was found that an endothermic
transition was observed at ca. 58°C in a wide range of concentrations.
The transition observed at 60°C is thermo-reversible and both temperature
and transition enthalpy are constant even after gel formation. Well equilibrated
suspension at a temperature lower than 60°C formed no gel. 相似文献