全文获取类型
收费全文 | 751篇 |
免费 | 46篇 |
出版年
2023年 | 4篇 |
2022年 | 9篇 |
2021年 | 20篇 |
2020年 | 13篇 |
2019年 | 16篇 |
2018年 | 16篇 |
2017年 | 19篇 |
2016年 | 28篇 |
2015年 | 44篇 |
2014年 | 43篇 |
2013年 | 50篇 |
2012年 | 55篇 |
2011年 | 60篇 |
2010年 | 35篇 |
2009年 | 35篇 |
2008年 | 32篇 |
2007年 | 34篇 |
2006年 | 39篇 |
2005年 | 29篇 |
2004年 | 31篇 |
2003年 | 18篇 |
2002年 | 24篇 |
2001年 | 18篇 |
2000年 | 11篇 |
1999年 | 14篇 |
1998年 | 11篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1970年 | 4篇 |
1969年 | 3篇 |
1968年 | 2篇 |
1967年 | 1篇 |
排序方式: 共有797条查询结果,搜索用时 734 毫秒
121.
122.
A synthetic method to triazole-fused sugars by treatment of nitroalkene-containing C-glycosides with sodium azide is described. Initial experiments conducted at room temperature gave only the 1,3-dipolar cycloaddition products. However, at elevated reaction temperature the tandem β-elimination/cycloaddition/Michael addition yielded 1,5-disubstituted triazole-fused sugars. 相似文献
123.
Muthu Manikandan Lejla Pašić Vijayaraghavan Kannan 《World journal of microbiology & biotechnology》2009,25(12):2247-2256
An extremely halophilic archaeon Haloferax lucentensis VKMM 007, isolated from a solar saltern, was found to produce a protease. This extracellular enzyme consisted of a single
polypeptide chain of 57.8 kDa as determined by SDS–PAGE and was purified by a combination of ultrafiltration, bacitracin–Sepharose
affinity chromatography and Sephadex G-100 gel filtration. The purified protein was stable in a wide range of temperatures
(20–70°C), NaCl concentrations (0.85–5.13 M) and pH (5.0–9.0) with maximal activity observed at 60°C, 4.3 M NaCl and pH 8.0.
Proteolytic activity was enhanced by Ca2+, K+, Mg2+, Na+, and Fe2+ ions and the protein was classified as a trypsin-like serine protease. Further assays indicated highest degree of specificity
when hemoglobin was used as an enzyme substrate. Most importantly, the proteolytic activity remained stable or only marginally
inhibited in the presence of various polar and non-polar solvents, surfactants and reducing agents thus emphasizing the biotechnological
potential of this novel halophilic protease. 相似文献
124.
Rishiram Ramanan Krishnamurthi Kannan Nadimuthu Vinayagamoorthy Kunga Mohan Ramkumar Saravana Devi Sivanesan Tapan Chakrabarti 《Biotechnology and Bioprocess Engineering》2009,14(1):32-37
Carbonic anhydrase enzyme, one of the fastest known enzymes, remains largely unexplored in prokaryotes when compared to its
mammalian counterparts despite its ubiquity. In this study, the enzyme has been purified from Bacillus subtilis SA3 using sequential Sephadex G-75 chromatography, DEAE cellulose chromatography, and sepharose-4B-L-tyrosinesulphanilamide
affinity chromatography and characterized to provide additional insights into its properties. The apparent molecular mass
of carbonic anhydrase obtained by SDS-PAGE was found to be approximately 37 kDa. Isoelectric focusing of the purified enzyme
revealed an isoelectric point (pI) of around 6.1 when compared with marker. The presence of metal ions such as Zn2+, Co2+, Cu2+, Fe3+, Mg2+, and anion SO4− increased enzyme activity while strong inhibition was observed in the presence of Hg2+, Cl−, HCO3−, and metal chelator EDTA. The optimum pH and temperature for the enzyme were found to be 8.3 and 37°C, respectively. Enzyme
kinetics with p-nitrophenyl acetate as substrate at pH 8.3 and 37°C determined the Vmax and Km values of the enzyme to be 714.28 μmol/mg protein/min and 9.09 mM, respectively. The Ki value for acetazolamide was 0.22 mM, compared to 0.099 mM for sulphanilamide. The results from N-terminal amino acid sequencing
imply the purified protein is a putative beta-carbonic anhydrase with close similarities to CAs from plants, microorganisms. 相似文献
125.
126.
Harding WW Schmidt M Tidgewell K Kannan P Holden KG Dersch CM Rothman RB Prisinzano TE 《Bioorganic & medicinal chemistry letters》2006,16(12):3170-3174
A synthetic sequence has been developed to selectively functionalize the furan ring of the natural product salvinorin A (2a). The synthetic routes described convert the furan ring in 2a into an N-sulfonylpyrrole, oxazole or an oxadiazole. In addition, a procedure has been found to remove the furan skeleton completely. Biological results indicate that replacement of the furan ring with an N-sulfonylpyrrole leads to reduced affinity and efficacy at kappa opioid receptors. 相似文献
127.
Das J Sitaram Kumar M Subrahmanyam D Sastry TV Prasad Narasimhulu C Laxman Rao CV Kannan M Roshaiah M Awasthi R Patil SN Sarnaik HM Rao Mamidi NV Selvakumar N Iqbal J 《Bioorganic & medicinal chemistry》2006,14(23):8032-8042
In an effort to discover potent antibacterials based on the entropically favored 'bioactive conformation' approach, a series of novel tricyclic molecules mimicking the conformationally constrained structure of Linezolid is reported. Based on the initial tricyclic molecule 1, the benzazepine derivative 2 was designed where the tricyclic structure had more flexibility around C-N bond compared to 1. While, the molecule 2 was less active, the molecule 3 showed promising antibacterial activity presumably after having obtained rigidity due to pyrrole ring. The syntheses, SAR studies, and evaluation of 3 as a lead compound are reported. 相似文献
128.
Previous studies have found that individuals from rural areas in Malaysia and in El Salvador prefer heavier women than individuals from urban areas. Several explanations have been proposed to explain these differences in weight preferences but no study has explored familiarity as a possible explanation. We therefore sought to investigate participants’ face preferences while also examining the facial characteristics of the actual participants. Our results showed that participants from rural areas preferred heavier-looking female faces than participants from urban areas. We also found that the female faces from the rural areas were rated as looking heavier than the female faces from the urban areas. Our findings are consistent with the hypothesis that familiarity may be contributing to the differences found in face preferences between rural and urban areas given that people from rural and urban areas are exposed to different faces. 相似文献
129.
130.
The present study was undertaken to determine the role of glutathione peroxidase3 (gpx3) in phospholipid protection in cells.
Wild-type (WT) cells showed an overall increase in phospholipids upon 50 μM cadmium (Cd)-treatment, whereas an untreated gpx3Δ strain showed a drastic reduction in overall phospholipids which was further reduced with 50 μM Cd. In WT cells, Cd-exposure
increased the short chain fatty acids and decreased the unsaturated fatty acids and the magnitude was high in Cd-treated gpx3Δ cells. Purified recombinant gpx3p showed higher activity with phospholipid hydroperoxides than shorter hydroperoxides. An
increase in gpx activity was observed in Cd-treated WT cells and no such alteration was observed in gpx3Δ. WT cells treated with Cd showed an increase in MDA over untreated, while untreated gpx3Δ cells themselves showed a higher level of MDA which was further enhanced with Cd-treatment. Iron, zinc and calcium levels
were significantly altered in WT and gpx3Δ cells during Cd-treatment. 相似文献