全文获取类型
收费全文 | 367篇 |
免费 | 22篇 |
国内免费 | 5篇 |
专业分类
394篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 6篇 |
2021年 | 7篇 |
2020年 | 10篇 |
2019年 | 16篇 |
2018年 | 9篇 |
2017年 | 6篇 |
2016年 | 8篇 |
2015年 | 13篇 |
2014年 | 17篇 |
2013年 | 29篇 |
2012年 | 13篇 |
2011年 | 17篇 |
2010年 | 10篇 |
2009年 | 10篇 |
2008年 | 15篇 |
2007年 | 18篇 |
2006年 | 15篇 |
2005年 | 15篇 |
2004年 | 7篇 |
2003年 | 14篇 |
2002年 | 5篇 |
2001年 | 10篇 |
2000年 | 6篇 |
1999年 | 10篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1996年 | 8篇 |
1995年 | 8篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 1篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有394条查询结果,搜索用时 0 毫秒
321.
AbstractIn this study, the different mole ratios of glucose oxidase/chitosan/dextran–aldehyde and glucose oxidase/chitosan/dextran–sulfate complexes were synthesized. The modification of glucose oxidase by non-covalent complexation with dextran and chitosan in different molar ratios was studied in order to increase the enzyme activity. The enzyme/polymer complexes obtained were investigated by UV spectrophotometer and dynamic light scattering. Activity determination of synthesized complexes and free enzyme were performed at a temperature range. The best results were obtained by Cchitosan/Cdextran–aldehyde = 10/1 ratio and Cchitosan/Cdextran–sulfate = 1/5 ratio that were used in thermal stability, shelf life, salt stress, and ethanol effect experiments. The results demonstrated that both complexes were thermally stable at 60?°C and had superior storage stability compared to the free glucose oxidase. Complexes showed higher enzymatic activity than free enzyme in the organic solvent environment using 10% ethanol. The complexes were resistant to salt stress containing 0.1?M NaCl or CaCl2. The particle size distribution results of the triple complex evaluated the complexation of the chitosan, dextran derivative, and glucose oxidase. The average size of the triple complex in diameter was found to be 325.8?±?9.3?nm. Overall findings suggest that the complexes of glucose oxidase, chitosan, and dextran showed significant enhancement in the enzyme activity. 相似文献
322.
323.
Fluorescein isothiocyanate was used to covalently label the gastric (H+ + K+)-ATPase. FITC treatment of the enzyme inhibited the ATPase activity while largely sparing partial reactions such as the associated activity. ATP protected against inhibition suggesting the ligand binds at or near an ATP binding site. At 100% inhibition the stoichiometry of binding was 1.5 nmol FITC per mg Lowry protein a value corresponding to maximal phosphoenzyme formation. Binding occurred largely to a peptide of 6.2 isoelectric point, although minor labelling of a peptide of 5.6 was also noted. Fluorescence was quenched by K+, Rb+ and Tl+ in a dose-dependent manner, and the values of 0.28, 0.83 and 0.025 mM correspond rather well to the values required for dephosphorylation at a luminal site. Vanadate, a known inhibitor of the gastric ATPase produced a slow Mg2+-dependent fluorescent quench. Ca2+ reversed the K+-dependent loss of fluorescence and inhibited it when added prior to K+. This may relate to the slow phosphorylation in the presence of ATP found when Ca2+ was substituted for Mg2+ and the absence of K+-dependent dephosphorylation. The results with FITC-modified gastric ATPase provide evidence for a conformational change with K+ binding to the enzyme. 相似文献
324.
The centipede Scolopendra subspinipes mutilans has been a medically important arthropod species by using it as a traditional medicine for the treatment of various diseases. In this study, we derived a novel lactoferricin B like peptide (LBLP) from the whole bodies of adult centipedes, S. s. mutilans, and investigated the antifungal effect of LBLP. LBLP exerted an antifungal and fungicidal activity without hemolysis. To investigate the antifungal mechanism of LBLP, a membrane study with propidium iodide was first conducted against Candida albicans. The result showed that LBLP caused fungal membrane permeabilization. The assays of the three dimensional flow cytometric contour plot and membrane potential further showed cell shrinkage and membrane depolarization by the membrane damage. Finally, we confirmed the membrane-active mechanism of LBLP by synthesizing model membranes, calcein and FITC-dextran loaded large unilamellar vesicles. These results showed that the antifungal effect of LBLP on membrane was due to the formation of pores with radii between 0.74 nm and 1.4 nm. In conclusion, this study suggests that LBLP exerts a potent antifungal activity by pore formation in the membrane, eventually leading to fungal cell death. 相似文献
325.
《Bioscience, biotechnology, and biochemistry》2013,77(12):3062-3065
Previously we reported that auraptene was a potent suppressant for matrix metalloproteinase (MMP)-7 expression in HT-29 human colon cancer cells. In the present study, we examined the effects of auraptene on MMP-2, -7, and -9 expression in colonic mucosa from dextran sulfate sodium (DSS)-induced ulcerative colitis mice. Auraptene remarkably suppressed the DSS-induced gelatinolytic activity of MMP-7 as well as the expression of MMP-2 and -9, suggesting that it might be useful in anti-metastatic therapies via the targeting of MMPs. 相似文献
326.
Jian-An Xian An-Li WangChao-Xia Ye Xiao-Dan ChenWei-Na Wang 《Comparative biochemistry and physiology. Toxicology & pharmacology : CBP》2010,152(2):182-188
The aim of this study was to investigate the cellular toxicity of copper-induced injury to the black tiger shrimp Penaeus monodon. The 24 h, 48 h, 72 h and 96 h LC50 (median lethal concentration) of Cu2+ on P. monodon (11.63 ± 1.14 g) were found to be 3.49, 1.54, 0.73 and 0.40 mg L− 1, respectively. Total haemocyte count (THC), phagocytic activity, respiratory burst (RB), cytoplasmic free-Ca2+ (cf-Ca2+) concentration and apoptotic cell ratio of shrimp were determined after exposure to different concentrations of Cu2+ (0, 0.05, 0.5, 1.5 and 3.5 mg L− 1) for 0, 6, 12, 24 and 48 h. There was no significant effect on the analytic indicator of shrimp exposed to 0.05 mg L− 1 Cu2+. THC decreased after Cu-exposure to 0.5 mg L− 1 for 48 h, 1.5 mg L− 1 for 24 h and 3.5 mg L− 1 for 12 h. Phagocytic activity decreased in P. monodon following 48 h exposure to 3.5 mg L− 1 Cu2+. RB was induced after 6 h exposure to 0.5, 1.5 and 3.5 mg L− 1 Cu2+. cf-Ca2+ concentration increased after 48 h exposure to 0.5 mg L− 1 Cu2+, and 12 h exposure to 1.5 and 3.5 mg L− 1 Cu2+. The percentage of apoptotic cells increased to 9.5%, 16.3% and 18.6% respectively following 48 h exposure to 0.5, 1.5 and 3.5 mg L− 1 Cu2+. These results indicate that Cu can induce oxidative stress, elevation of cf-Ca2+ and cell apoptosis, and inhibit phagocytic activity in the shrimp P. monodon, and the lethal injury of Cu2+ to P. monodon may be mainly due to the sharp reduction of THC caused by ROS-induced apoptosis. 相似文献
327.
Flemmig J Zschaler J Remmler J Arnhold J 《The Journal of biological chemistry》2012,287(33):27913-27923
The specific detection of peroxidase activity in human granulocytes is essential to elucidate their role in innate immune responses, immune regulation, and inflammatory diseases. The halogenating activity of myeloperoxidase in neutrophils can be determined by the novel fluorescent probe aminophenyl fluorescein (APF). Thereby non-fluorescent APF is oxidized by HOCl to form fluorescein. We successfully verified that APF equally detects the hypobromous acid (HOBr)-producing activity of eosinophil granulocytes. This was revealed by three different approaches. First, we investigated the conversion of non-fluorescent APF into fluorescein by HOCl and HOBr by means of fluorescence and mass spectrometry approaches. Thereby comparable chemical mechanisms were observed for both acids. Furthermore in vitro kinetic studies were used to detect the halogenating activity of myeloperoxidase and eosinophil peroxidase by using APF. Here the dye well reflected the different substrate specificities of myeloperoxidase and eosinophil peroxidase regarding chloride and bromide. Finally, peroxidase activities were successfully detected in phorbol ester-stimulated neutrophils and eosinophils using flow cytometry. Thereby inhibitory studies confirmed the peroxidase-dependent oxidation of APF. To sum up, APF is a promising tool for further evaluation of the halogenating activity of peroxidases in both neutrophils and eosinophils. 相似文献
328.
Fatty acid synthetase has been purified from Cryptococcus neoformans 450 fold to a specific activity of 3.6 units per mg protein with an overall yield of 23%. The purified enzyme contained two non-identical subunits, Mr approximately 2.1×105 and 1.8×105. Under optimum conditions, 100 mM KCl and pH 7.5, apparent Km values for the substrates were: Acetyl CoA, 19 M; Malonyl CoA, 5 M; and NADPH, 6 M. Product inhibition patterns were determined to be: CoA, competitive versus acetyl CoA and malonyl CoA, uncompetitive versus NADPH; NADP, competitive versus NADPH, uncompetitive versus acetyl CoA and malonyl CoA; Palmitoyl CoA, competitive versus malonyl CoA, noncompetitive versus acetyl CoA and NADPH; Bicarbonate, uncompetitive versus malonyl CoA. These product inhibition patterns are consistent with the multisite ping-pong mechanism previously proposed for the avian fatty acid synthetase complex. The cryptococcal fatty acid synthetase was inhibited by the polyanionic polymers, heparin and dextran sulfate, an effect never before demonstrated for a fatty acid synthetase. This inhibition exhibited a marked dependence on the length of the polymer chain, with dextran sulfate fractions with Mr of 6×105 and above having K
i
values below 100 nanomolar. A model is presented that involves initial binding of the anionic polymer to the enzyme complex at a region of high positive charge density, followed by interaction of the end of the tethered polymer with the catalytic site. This study represents the first purification of fatty acid synthetase from a basidiomycete. 相似文献
329.
Dextran was covalently coupled to neutral unilamellar liposomes. Dextran conjugated liposomes were cleared from the circulation
at a much slower rate than unconjugated liposomes. The uptake of dextran conjugated liposomes by liver and spleen was also
decreased. The amount of dextran on the surface of liposomes was found to be a determining factor for their stability in circulation.
Dextran conjugated liposomes therefore may be a more effective way of controlled drug release 相似文献
330.