全文获取类型
收费全文 | 1035篇 |
免费 | 50篇 |
国内免费 | 68篇 |
出版年
2024年 | 1篇 |
2023年 | 12篇 |
2022年 | 16篇 |
2021年 | 16篇 |
2020年 | 29篇 |
2019年 | 27篇 |
2018年 | 18篇 |
2017年 | 35篇 |
2016年 | 25篇 |
2015年 | 18篇 |
2014年 | 31篇 |
2013年 | 120篇 |
2012年 | 51篇 |
2011年 | 68篇 |
2010年 | 30篇 |
2009年 | 50篇 |
2008年 | 58篇 |
2007年 | 55篇 |
2006年 | 81篇 |
2005年 | 55篇 |
2004年 | 46篇 |
2003年 | 48篇 |
2002年 | 36篇 |
2001年 | 28篇 |
2000年 | 28篇 |
1999年 | 28篇 |
1998年 | 17篇 |
1997年 | 18篇 |
1996年 | 12篇 |
1995年 | 16篇 |
1994年 | 15篇 |
1993年 | 11篇 |
1992年 | 6篇 |
1991年 | 11篇 |
1990年 | 7篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有1153条查询结果,搜索用时 223 毫秒
101.
102.
In vitro study of alginate–chitosan microcapsules: an alternative to liver cell transplants for the treatment of liver failure 总被引:7,自引:0,他引:7
Haque T Chen H Ouyang W Martoni C Lawuyi B Urbanska AM Prakash S 《Biotechnology letters》2005,27(5):317-322
The application of alginate–chitosan (AC) microcapsules to liver cell transplantation has not been previously investigated. In the current in vitro study, we have investigated the potential of AC microcapsules for the encapsulation of liver cells and show that the AC membrane supports the survival, proliferation and protein secretion by entrapped hepatocytes. The AC membrane provides cell immuno-isolation and has the potential for cell cryopreservation. The AC microcapsule has several advantages compared to more widely used alginate–poly-L-lysine (APA) microcapsules for the application of cell therapy. 相似文献
103.
Köping-Höggård M Issa MM Köhler T Tronde A Vårum KM Artursson P 《The journal of gene medicine》2005,7(9):1215-1222
BACKGROUND: The available methods for administration of gene delivery systems to the lungs of small animals via nebulization have several drawbacks. These include lack of control over the delivered dose and a negative impact on the stability of the formulation. This paper describes a new nebulization catheter device for the administration of plasmid-based gene delivery systems (polyplexes) as aerosols to the mouse lung in vivo. METHODS: The physical stability of naked pDNA and polyplexes formulated with chitosan oligomers and PEI was examined following nebulization with the catheter device. We also examined the in vitro transfection efficiency of the polyplexes recovered after nebulization. Lung distribution and gene expression after administration of the selected gene delivery systems to the mouse lung were also investigated. RESULTS: In contrast to previously described nebulization methods, the structural integrity of the unprotected naked pDNA was maintained following nebulization by the catheter device, which indicates relatively mild nebulization conditions. In addition, the nebulization procedure did not affect the physical stability of the formulated polyplexes. Small volumes of the pDNA aerosol (10-20 microl) were delivered in a highly controlled and reproducible manner. The aerosol droplet size varied with the molecular weight of the polycations. Aerosol delivery via this method resulted in improved lung distribution of pDNA polyplexes and a six-fold increase in the efficiency of gene delivery in vivo over that seen with the commonly used intratracheal instillation method. CONCLUSION: The use of the nebulization catheter device provides a promising alternative for aerosol gene delivery to the mouse lung. 相似文献
104.
Isolation of glycopeptides utilizing hydrogen bonding between glycopeptide glycans and a carbohydrate-gel matrix in the organic phase is useful for site-specific characterization of oligosaccharides of glycoproteins, when combined with mass spectrometry. In this study, recovery of glycopeptides was improved by including divalent cations or increasing the organic solvent in the binding solution, without losing specificity, whereas it was still less effective for those with a long peptide backbone exceeding 50 amino acid residues. The method was then applied to the analysis of glycan heterogeneities at seven N-glycosylation sites in each of the plasma and cellular fibronectins (FNs). There was a remarkable site-specific difference in fucosylation between these isoforms; Asn1244 selectively escaped the global fucosylation of cellular FN, whereas only Asn1007 and Asn2108 of the plasma isoform underwent modification. In addition, a new O-glycosylation site was identified at Thr279 in the connecting segment between the fibrin- and heparin-binding domain and the collagen-binding domain, and the glycopeptide was reactive to a peanut agglutinin lectin. Considering that another mucin-type O-glycosylation site lies within a different connecting segment, the O-glycosylation of FN was suggested to play a significant role in segregating the neighboring domains and thus maintaining the topology of FN and the domain functions. In addition, the method was applied to apolipoprotein B-100 (apoB100) whose N-glycan structures at 17 of 19 potential sites have been reported, and characterized the remaining sites. The results also demonstrated that the enriched glycopeptide provides resources for site-specific analysis of oligosaccharides in glycoproteomics. 相似文献
105.
In order to study the relationship between chemical structure and properties of modified carrageenans versus antioxidant activity in vitro, kappa-carrageenan oligosaccharides were prepared through mild hydrochloric acid hydrolysis of the polysaccharide, and these were used as starting materials for the partial synthesis of their oversulfated, acetylated, and phosphorylated derivatives. The structure and substitution pattern of the oligosaccharides and their derivatives were studied using FTIR and (13)C NMR spectroscopy, and their in vitro antioxidant activities were investigated. Certain derivatives of the carrageenan oligosaccharides exhibited higher antioxidant activity than the polysaccharides and oligosaccharides in certain antioxidant systems. The oversulfated and acetylated derivatives, which scavenge superoxide radicals, the phosphorylated and low-DS acetylated derivatives, which scavenge hydroxyl radicals, and the phosphorylated derivatives, which scavenge DPPH radicals, all exhibited significant antioxidant activities in the systems examined. The effect of the molecular weight of the carrageenan on antioxidant activities, however, is not obvious from these studies. 相似文献
106.
Structural analysis of the core oligosaccharide from Pasteurella multocida strain X73 总被引:1,自引:0,他引:1
The structure of the core oligosaccharide region of the lipopolysaccharide from the Pasteurella multocida strain X73 was elucidated. The lipopolysaccharide was subjected to a variety of degradative procedures. The structure of the purified oligosaccharide was established by monosaccharide and methylation analyses, NMR spectroscopy and mass spectrometry. The following structure illustrates a similar structure to the recently identified oligosaccharide from another P. multocida strain VP161, but with additional symmetrical substitution of the terminal galactose residues with phosphoethanolamine moieties, where based on the NMR data all sugars were found in pyranose ring forms and Kdo is 3-deoxy-alpha-D-manno-2-oct-2-ulosonic acid, l,D-alpha-Hep is l-glycero-D-manno-heptose, PEtn is phosphoethanolamine and PCho is phosphocholine. 相似文献
107.
壳聚糖具有抑菌性与成膜性。将壳聚糖辐照降解得到的一系列不同粘均分子量产物进行涂膜草莓保鲜,研究涂膜液中壳聚糖粘均分子量、浓度、pH值、有机酸、明胶含量对草莓保鲜效果的影响;并设计四因素三水平正交试验。实验结果表明:1%(w/v)7.0×10^4Da壳聚糖、1%(v/v)醋酸、pH5、添加明胶0.5%的涂膜配方具有最好的保鲜效果;在常温(20℃、湿度80%~90%)下可以延长贮藏期2d;低温(3℃-4℃、湿度80%-90%)下可以延长贮藏期3d。 相似文献
108.
M.Kaniz Fatema Diogo R.B. Ducatti M. Eug?nia R. Duarte Alberto S. Cerezo María C. Matulewicz 《Carbohydrate research》2010,345(2):275-2314
MALDI-TOF mass spectrometry analyses of several oligosaccharides (aldoses) and oligosaccharide alditols derived from agaroses, kappa- and iota-carrageenans using different matrices (2,5-dihydroxybenzoic acid, nor-harmane, ferulic acid, and the ionic liquid matrices 2,5-dihydroxybenzoic acid-n-butylamine and ferulic acid-n-butylamine) were conducted. These carbohydrates were selected as model compounds to study the MALDI prompt and post-source decay (PSD) fragmentation processes of both families of oligosaccharides. Sulfated alditols showed in the negative-ion mode the molecular ion as [M−Na]− together with the species yielded by their prompt fragmentation (mainly desulfation) while the sulfated oligosaccharides (aldoses) showed mainly glycosidic prompt fragmentation (glycosidic C-cleavages and desulfation). Non-sulfated aldoses and alditols, which could only be analyzed in positive-ion mode ([M+Na]+), did not suffer any prompt fragmentation. The former yielded cross-ring fragmentation in the PSD mode. Best results were obtained by using 2,5-dihydroxybenzoic acid and/or nor-harmane as matrices for all the compounds studied. 相似文献
109.
Georgios N. Hatzopoulos 《FEBS letters》2010,584(5):1011-1015
The crystal structure of the free form of IF1 from Mycobacterium tuberculosis has been determined at 1.47 Å resolution. The structure adopts the expected OB fold and matches the high structural conservation among IF1 orthologues. In order to further explore the function of Mtb-IF1, we built a model of its interaction with the 30S ribosomal subunit based on the crystal structure of the complex from Thermus thermophilus. The model suggests that several functionally important side chain residues undergo large movements while the rest of the protein in complex shows only very limited conformational change as compared to its form in solution. 相似文献
110.
Immunogenicity of synthetic saccharide fragments of Vibrio cholerae O1 (Ogawa and Inaba) bound to Exotoxin A 总被引:1,自引:0,他引:1
Wade TK Saksena R Shiloach J Kovác P Wade WF 《FEMS immunology and medical microbiology》2006,48(2):237-251
Recombinant exotoxin A (rEPA) from Pseudomonas aeruginosa conjugated to Vibrio cholerae O1 serotype-specific polysaccharides (mono-, di- and hexasaccharide) were immunogenic in mice. Monosaccharide conjugates boosted the humoral responses to the hexasaccharide conjugates. Prior exposure to purified Ogawa lipopolysaccharide (LPS) enabled contra-serotype hexasaccharide conjugates to boost the vibriocidal response, but Inaba LPS did not prime for an enhanced vibriocidal response by a contra-serotype conjugate. Prior exposure to the carrier, and priming B cells with the LPS of either serotype, resulted in enhanced vibriocidal titers if the Ogawa hexasaccharides were used, but a diminished response to the Inaba LPS. These studies demonstrate that the 'functional' B cell epitopes on the LPS differ from those of the neoglycoconjugates and that the order of immunization and the serotype of the boosting conjugate can influence the epitope specificity and function of the antisera. 相似文献