全文获取类型
收费全文 | 589篇 |
免费 | 40篇 |
国内免费 | 47篇 |
出版年
2024年 | 1篇 |
2023年 | 9篇 |
2022年 | 11篇 |
2021年 | 11篇 |
2020年 | 23篇 |
2019年 | 21篇 |
2018年 | 15篇 |
2017年 | 25篇 |
2016年 | 14篇 |
2015年 | 12篇 |
2014年 | 26篇 |
2013年 | 68篇 |
2012年 | 39篇 |
2011年 | 41篇 |
2010年 | 20篇 |
2009年 | 29篇 |
2008年 | 44篇 |
2007年 | 29篇 |
2006年 | 56篇 |
2005年 | 32篇 |
2004年 | 25篇 |
2003年 | 27篇 |
2002年 | 13篇 |
2001年 | 15篇 |
2000年 | 15篇 |
1999年 | 13篇 |
1998年 | 3篇 |
1997年 | 7篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1980年 | 1篇 |
排序方式: 共有676条查询结果,搜索用时 15 毫秒
101.
The purpose of this study was to investigate the formulation variables influencing the drug release from the layered tablets
containing chitosan and xanthan gum as matrix component. Increasing the amount of lactose could diminish pH sensitive release
behavior of these matrix tablets. Effect of formulation variables on drug release from the prepared three-layered matrix tablets
was investigated. The amount of drug loading did not affect the drug release which was influenced by the hydrodynamic force
and the matrix composition. An increase in stirring rate correspondingly increased the release rate. Moreover, incorporation
of soluble diluents in core or barrier could enhance the drug release. Least square fitting the experimental dissolution data
to the mathematical expressions (power law, first order, Higuchi’s and zero order) was carried out to study the drug release
mechanism. Most dissolution profiles of the prepared three-layered tablets provided a better fit to zero order kinetic than
to first order kinetic and Higuchi’s equation. 相似文献
102.
N. R. Kildeeva P. A. Perminov L. V. Vladimirov V. V. Novikov S. N. Mikhailov 《Russian Journal of Bioorganic Chemistry》2009,35(3):360-369
The regularities of the reaction of aminopolysaccharide chitosan with glutaraldehyde (GA) have been considered. The equilibrium forms of GA in water have been thoroughly studied by NMR spectroscopy. It has been established that at pH 5.6, the exchange of the protons of O=CHCH2 groups for deuterium occurs, indicating the presence of an anion, a product of the first stage of the aldol reaction; at pH > 7.2, the formation of the products of an aldol reaction and aldol condensation takes place. The kinetics of the reaction between the amino groups of chitosan and GA, the kinetics of gel formation in chitosan solutions in the presence of GA, and the kinetics of changes in the rigidity of gels formed have been studied by UV spectroscopy. IR spectra of cross-linked chitosan have been obtained. It has been shown that chitosan catalyzes the polymerization of GA to form irregular products; in this process, the length of oligomeric chains in modified or cross-linked chitosan and the concentration of conjugated bonds increase with the GA concentration and pH of the reaction medium. 相似文献
103.
Lu Huang Xiaojie Cheng Chengsheng Liu Ke Xing Jing Zhang Gangzheng Sun Xiaoyan Li Xiguang Chen 《生物学前沿》2009,4(3):321-327
An oleic acid-grafted chitosan oligosaccharide (CSO-OA) with different degrees of amino substitution (DSs) was synthesized by the 1-ethyl-3-(3-dimethylami-nopropyl) carbodiimide (EDC)-mediated coupling reac-tion. Fourier transform infrared spectroscopy (FT-IR) suggested the formation of an amide linkage between amino groups of chitosan oligosaccharide and carboxyl groups of oleic acid. The critical aggregation concentra-tions (CACs) of CSO-OA with 6%, 11%, and 21% DSs were 0.056, 0.042, and 0.028mg·mL-1, respectively. Nanoparticles prepared with the sonication method were characterized by means of transmission electron micro-scopy (TEM) and Zetasizer, and the antibacterial activity against Escherichia coli and Staphylococcus aureus was investigated. The results showed that the CSO-OA nanoparticles were in the range of 60-200 nm with satisfactory structural integrity. The particle size slightly decreased with the increase of DS of CSO-OA. The antibacterial trial showed that the nanoparticles had good antibacterial activity against E. coli and S. aureus. 相似文献
104.
Himanshu Gupta M. Aqil R. K. Khar Asgar Ali Aseem Bhatnagar Gaurav Mittal Sanyog Jain 《AAPS PharmSciTech》2009,10(2):540-546
In situ gel-forming systems have drawn much attention of current researchers to overcome the poor bioavailability from the conventional
eye drops. The present work described formulation and pharmacoscintigraphic evaluation of timolol-maleate-loaded chitosan/hydroxy
propyl methyl cellulose (HPMC)-based polymer matrix for enhanced ocular retention. Chitosan and HPMC ratio was optimized and
formulation was characterized for various in vitro parameters. The ocular retention was studied on New Zealand rabbits by gamma scintigraphy, which is a very simple and noninvasive
technique. For scintigraphy study, the drug timolol maleate was radiolabeled 99mTc by direct labeling method using SnCl2·2H2O as reducing agent. The labeling procedure was optimized to get maximum labeling efficiency (>98%). In vitro stability of the radiolabeled drug (99mTc-timolol maleate complex) was checked and it was found to be stable for up to 24 h. Plain drug eliminates rapidly as significant
activity was recorded in kidney and bladder after 2 h of ocular administration. It was evident from the scintigraphic images
and the time–activity curve plotted from the data that the plain drug solution cleared very rapidly from the corneal region
and reached into systemic circulation via nasolachrymal drainage system, as significant activity was recorded in kidney and
bladder after 2 h of ocular administration. Developed formulation cleared at a slow rate and remained at corneal surface for
longer time duration. No radioactivity was observed in systemic circulation after 2 h. Ocular irritation of the developed
formulation was also checked by hen’s egg chorioallantoic membrane test and formulation was found to be practically nonirritant.
The study signified the potential of gamma scintigraphy in evaluation of novel drug delivery systems in a noninvasive manner. 相似文献
105.
The different approaches for targeting orally administered drugs to the colon include coating with pH-dependent polymers,
design of time-release dosage forms, and the utilization of carriers that are degraded exclusively by colonic bacteria. The
aim of the present study was to develop a single unit, site-specific drug formulation allowing targeted drug release in the
colon. Matrix tablets were prepared by wet granulation using cross-linked chitosan (ChI) and chondroitin sulfate (ChS) polysaccharides
as binder and carrier. ChS was used to form polyelectrolyte complexes (PEC) with ChI, and its potential as a colon-targeted
drug carrier was investigated. Indomethacin was used as a model drug. The ChI and ChS PEC was characterized by Fourier transform
infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and powder X-ray diffraction studies (XRD). The matrix
tablets were tested in vitro for their suitability as colon-specific drug delivery systems. FTIR demonstrated that the PEC forms through an electrostatic
interaction between the protonated amine (NH3+) group of ChI with the free carboxylate (COO−) group and sulfate (SO42−) group of ChS. DSC and XRD indicated that the PEC has different thermal characteristics from ChI or ChS. The dissolution
data demonstrates that the dissolution rate of the tablet is dependent upon the concentration of polysaccharide used as binder
and matrix and time of cross-linking. The study confirmed that selective delivery of indomethacin to the colon can be achieved
using cross-linked ChI and ChS polysaccharides. 相似文献
106.
通过醋酸-H2O2氧化降解法制备三种不同特性粘数(50℃时,η=4.76mL/g,29.39mL/g和54.93mL/g)的壳聚糖。以小鼠为实验对象,采取灌胃给药方式,考察其降低血浆TCH、TG的能力,并以血浆SOD酶活及MDA含量为指标,进行抗氧化药效学评价。结果显示,给药21d后,三种壳聚糖均能显著降低小鼠血浆TCH和TG含量,降幅分别大于28.2%和22.5%;且三种壳聚糖也能显著降低小鼠血浆MDA含量,降幅大于30.0%,但对小鼠血浆SOD酶活则无显著影响。 相似文献
107.
108.
基于细胞实验研究壳聚糖(chitosan,CS)薄膜成球培养技术对间充质干细胞(mesenchymal stem cells, MSCs)迁徙趋化特性的影响。从脐带组织中分离原代MSCs采取CS成球法培养,以常规贴壁培养MSCs作为对照,72 h后收集两组细胞分别进行划痕实验、Tranthwell迁徙实验观察并拍照记录,RT-PCR方法检测两种培养方式中MSCs迁徙相关基因表达水平的差异。研究结果显示,相较常规贴壁培养方式,CS培养组MSCs体外迁徙趋化能力增强,差异具有显著统计学意义(P<0.01);CS成球培养组MSCs 中CXCR4、CXCR7、MCP-1、MMP-1、MMP-2、MMP-9、TIMP-2等迁徙相关基因表达均明显上调(P<0.01)。实验表明CS成球培养可显著促进MSCs的迁移趋化特性。 相似文献
109.
Dario Rafael Olicón-Hernández Pedro Alberto Vázquez-Landaverde Ramón Cruz-Camarillo 《Preparative biochemistry & biotechnology》2017,47(2):116-122
Bacillus thuringiensis is a nonhuman pathogen bacterium that is used as a fungal and insect biocontrol agent. Because of its environmental interaction, it possesses several extracellular enzymes that are able to degrade chitin and chitosan, two of the most important polymers because of their application in numerous fields. However, in recent years, it has been observed that oligosaccharides from the enzymatic degradation of chitosan have important benefits for human health. Comparison and exploration of the production of chito-oligosaccharides from different sources of chitosan will improve the process parameters and expand the biotechnology based in these molecules. This study shows the production of chito-oligosaccharides from three different sources of colloidal chitosan and conducts a qualitative–quantitative comparison between them, using the extracellular enzyme of B. thuringiensis. We found that in the three substrates, it is possible to get a mixture of chito-oligosaccharides from dimer to hexamer in a concentration range from 0.72 to 8.09?mg?·?g?1 of original substrate. The best substrate to obtain these molecules was commercial chitosan as it has the highest production yields. 相似文献
110.