全文获取类型
收费全文 | 794篇 |
免费 | 33篇 |
出版年
2023年 | 3篇 |
2022年 | 10篇 |
2021年 | 13篇 |
2020年 | 8篇 |
2019年 | 8篇 |
2018年 | 19篇 |
2017年 | 11篇 |
2016年 | 19篇 |
2015年 | 35篇 |
2014年 | 36篇 |
2013年 | 44篇 |
2012年 | 63篇 |
2011年 | 53篇 |
2010年 | 39篇 |
2009年 | 27篇 |
2008年 | 28篇 |
2007年 | 47篇 |
2006年 | 34篇 |
2005年 | 47篇 |
2004年 | 34篇 |
2003年 | 38篇 |
2002年 | 42篇 |
2001年 | 13篇 |
2000年 | 11篇 |
1999年 | 17篇 |
1998年 | 8篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 6篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1990年 | 7篇 |
1989年 | 3篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 11篇 |
1978年 | 3篇 |
1977年 | 8篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1971年 | 3篇 |
1970年 | 4篇 |
1969年 | 2篇 |
排序方式: 共有827条查询结果,搜索用时 15 毫秒
51.
An efficient protocol was developed for qualitative screening of phosphate-solubilizing bacteria, based upon visual observation.
Our results indicate that, by using our formulation containing bromophenol blue, it is possible to quickly screen on a qualitative
basis the phosphate-solubilizing bacteria. Qualitative analysis of the phosphate solubilized by various groups correlated
well with grouping based upon quantitative analysis of bacteria isolated from soil, effect of carbon, nitrogen, salts, and
phosphate solubilization-defective transposon mutants. However, unlike quantitative analysis methods that involve time-consuming
biochemical procedures, the time for screening phosphate-solubilizing bacteria is significantly reduced by using our simple
protocol. Therefore, it is envisaged that usage of this formulation based upon qualitative analysis will be salutary for the
quick screening of phosphate-solubilizing bacteria. Our results indicate that the formulation can also be used as a quality
control test for expeditiously screening the commercial bioinoculant preparations, based on phosphate solubilizers.
Received: 17 November 2000 / Accepted: 22 December 2000 相似文献
52.
We describe the design and synthesis of a novel well characterized multi-peptide conjugate (MPC) system containing antigens from human malaria parasite and the Tat protein of HIV type-1 (HIV-1-Tat). Construction of the MPC utilizes Fmoc solid-phase peptide synthesis coupled with solution chemistry. In the first phase, a core template that serves as primary anchor for the synthesis and attachment of multiple antigens is synthesized. Serine(trityl) and multiple lysine branches with epsilon groups blocked during chain assembly are incorporated forming a tetrameric core. Cysteine whose side chain thiol serves to couple haloacetyl or S-protected haloacetyl peptides is added to complete assembly of the core template. Modification to the coupling solvent, addition of key amino acid derivatives (N-[1-hydroxy-4-methoxybenzyl]) in the peptide sequence allows the synthesis of base peptides on the core template with molecular mass greater than 7500 kDa. Base peptides are then reacted with high performance liquid chromatography purified haloacetyl peptides to generate multiple peptide conjugates with molecular masses of 10 to 13 kDa. MPC constructs thus formed are further characterized by matrix assisted laser desorption-time of flight mass spectroscopy (MALDI-MS), amino acid analysis, size exclusion chromatography, and SDS-polyacrylamide gel electrophoresis (PAGE). To our knowledge, this is the first report describing a chemically well defined multiple conjugate system with potential for development of synthetic subunit vaccines. 相似文献
53.
Menthol is a highly valued monoterpene produced by Japanese mint (Mentha arvensis) as a natural product with wide applications in cosmetics, confectionery, flavours, beverages and therapeutics. Selection
of high menthol yielding genotypes is therefore the ultimate objective of all genetic improvement programmes inMentha arvensis. A positive correlation was observed in the present study between menthol content in oils of evaluated genotypes and the
level of tolerance to externally supplied menthol of explants of these genotypes in culture medium. The easy use of this relationship
as a selectable biochemical marker opens the practical applicability of largescalein vitro screening of the germplasm, clones and breeders' material for selection of elite genotypes. 相似文献
54.
Gastropathy and defense mechanisms in common bile duct ligated portal hypertensive rats 总被引:6,自引:0,他引:6
Kaur S Kaur U Tandon C Dhawan V Ganguly NK Majumdar S 《Molecular and cellular biochemistry》2000,203(1-2):79-85
Portal hypertensive gastropathy is associated with a broad spectrum of gastric mucosal damage inspite of decreased gastric acid secretion, suggestive of compromised endogenous protective mechanisms. To determine the mechanisms of damage in portal hypertensive gastropathy we measured lipid peroxidation, glutathione, antioxidant and lysosomal enzymes in gastric mucosal homogenates from male Wistar rats with elevated intrasplenic pulp pressure, eighteen days after common bile duct ligation. Thiobarbituric acid-reactive substances and lysosomal enzymes (-glucuronidase and acid phosphatase) were increased in the common bile duct ligated group as compared to the sham-operated group. The levels of antioxidant defense enzymes, superoxide dismutase, glutathione peroxidase, catalase and glutathione were decreased as compared to the sham-operated controls. Pre-operative vitamin E administration decreased mucosal lipid peroxidation increased the levels of antioxidant defense enzymes and lowered the lysosomal enzymes. The plasma vitamin E levels in this group were lower when compared to animals receiving it post-operatively. In conclusion, free radical and lysosomal enzyme mediated damage may play a role in portal hypertensive gastropathy. 相似文献
55.
Garton SD Temple CA Dhawan IK Barber MJ Rajagopalan KV Johnson MK 《The Journal of biological chemistry》2000,275(10):6798-6805
Resonance Raman spectroscopy has been used to define active site structures for oxidized Mo(VI) and reduced Mo(IV) forms of recombinant Rhodobacter sphaeroides biotin sulfoxide reductase expressed in Escherichia coli. On the basis of (18)O/(16)O labeling studies involving water and the alternative substrate dimethyl sulfoxide and the close correspondence to the resonance Raman spectra previously reported for dimethyl sulfoxide reductase (Garton, S. D., Hilton, J., Oku, H., Crouse, B. R., Rajagopalan, K. V., and Johnson, M. K. (1997) J. Am. Chem. Soc. 119, 12906-12916), vibrational modes associated with a terminal oxo ligand and the two molybdopterin dithiolene ligands have been assigned. The results indicate that the enzyme cycles between mono-oxo-Mo(VI) and des-oxo-Mo(IV) forms with both molybdopterin dithiolene ligands remaining coordinated in both redox states. Direct evidence for an oxygen atom transfer mechanism is provided by (18)O/(16)O labeling studies, which show that the terminal oxo group at the molybdenum center is exchangeable with water during redox cycling and originates from the substrate in substrate-oxidized samples. Biotin sulfoxide reductase is not reduced by biotin or the nonphysiological products, dimethyl sulfide and trimethylamine. However, product-induced changes in the Mo=O stretching frequency provide direct evidence for a product-associated mono-oxo-Mo(VI) catalytic intermediate. The results indicate that biotin sulfoxide reductase is thermodynamically tuned to catalyze the reductase reaction, and a detailed catalytic mechanism is proposed. 相似文献
56.
A series of oligomers of polyamides based on 14-amino-3,6,9, 12-tetraoxatetradecanoic acid monomers (ATTAn) was synthesized. These materials were designed as monodisperse analogues of poly(ethylene glycol) for use in biomedical applications where reproducible behavior is important. Synthesis of the monomer was evaluated using two routes. For small-scale preparations, tetraethylene glycol (TEG) was monoprotected with dihydropyran, converted to an alkoxide, and alkylated with ethyl bromoacetate. On larger scales, TEG was alkylated directly by treatment with sodium, followed by ethyl bromoacetate. The amine function was introduced by mesylation followed by treatment with sodium azide. Reduction of the azide to amino groups was performed over Pd/C using either hydrogen or formic acid as proton sources. Assembly of the oligomers was accomplished using standard DCC/NHS chemistry and an iterative dimerization sequence after appropriate deprotection of a pair of monomers. The amino group was protected by retaining the azido group as a latent amine. A series of ATTAn oligomers was prepared (n = 1-8). A lipid conjugate of the octamer, ATTA8-DSPE, was synthesized. 相似文献
57.
58.
Ajit Kumar Shasany Suman P. S. Khanujia Sunita Dhawan Usha Yadav Srikant Sharma Sushil Kumar 《Journal of biosciences》1998,23(5):641-646
Media and incubation conditions have been defined for highly efficient regeneration of shoots from internode explants of slow
and fast growing cultivars ofMentha arvensis. Internodal segments excised from thein vitro raised shoots were inoculated on the MS medium supplemented with combinations of 5 concentrations of l-napthalene acetic
acid (NAA) and 3 concentrations of 6-benzyl amino purine (BAP). The media containing 2 μg ml−1 NAA, 10 Μg ml−1 BAP and 1 μg ml−1 NAA, 5 μg ml−1 BAP proved best for shoot regeneration and growth responses on cv Himalaya and cv Kalka explants, respectively. In 12 weeks
time, on average one explant of cv Himalaya produced about 200 shoots and that of cv Kalka produced about 180 shoots. The
Himalaya explants required higher concentrations of NAA and BAP for high efficiency proliferation as compared to the Kalka
explants. The experiments demonstrated that internodal tissue inMentha arvensis can be induced to obtain direct shoot regenerants with high efficiency. The analysis of the RAPD profiles of 100 regenerated
plantlets each of cv Himalaya and Kalka showed more than 99.9% homogeneity in bands with respect to the parents. 相似文献
59.
Mylarappa Ningappa Juhoon So Joseph Glessner Chethan Ashokkumar Sarangarajan Ranganathan Jun Min Brandon W. Higgs Qing Sun Kimberly Haberman Lori Schmitt Silvia Vilarinho Pramod K. Mistry Gerard Vockley Anil Dhawan George K. Gittes Hakon Hakonarson Ronald Jaffe Shankar Subramaniam Donghun Shin Rakesh Sindhi 《PloS one》2015,10(9)
Background & Aims
Altered extrahepatic bile ducts, gut, and cardiovascular anomalies constitute the variable phenotype of biliary atresia (BA).Methods
To identify potential susceptibility loci, Caucasian children, normal (controls) and with BA (cases) at two US centers were compared at >550000 SNP loci. Systems biology analysis was carried out on the data. In order to validate a key gene identified in the analysis, biliary morphogenesis was evaluated in 2-5-day post-fertilization zebrafish embryos after morpholino-antisense oligonucleotide knockdown of the candidate gene ADP ribosylation factor-6 (ARF6, Mo-arf6).Results
Among 39 and 24 cases at centers 1 and 2, respectively, and 1907 controls, which clustered together on principal component analysis, the SNPs rs3126184 and rs10140366 in a 3’ flanking enhancer region for ARF6 demonstrated higher minor allele frequencies (MAF) in each cohort, and 63 combined cases, compared with controls (0.286 vs. 0.131, P = 5.94x10-7, OR 2.66; 0.286 vs. 0.13, P = 5.57x10-7, OR 2.66). Significance was enhanced in 77 total cases, which included 14 additional BA genotyped at rs3126184 only (p = 1.58x10-2, OR = 2.66). Pathway analysis of the 1000 top-ranked SNPs in CHP cases revealed enrichment of genes for EGF regulators (p<1 x10-7), ERK/MAPK and CREB canonical pathways (p<1 x10-34), and functional networks for cellular development and proliferation (p<1 x10-45), further supporting the role of EGFR-ARF6 signaling in BA. In zebrafish embryos, Mo-arf6 injection resulted in a sparse intrahepatic biliary network, several biliary epithelial cell defects, and poor bile excretion to the gall bladder compared with uninjected embryos. Biliary defects were reproduced with the EGFR-blocker AG1478 alone or with Mo-arf6 at lower doses of each agent and rescued with arf6 mRNA.Conclusions
The BA-associated SNPs identify a chromosome 14q21.3 susceptibility locus encompassing the ARF6 gene. arf6 knockdown in zebrafish implicates early biliary dysgenesis as a basis for BA, and also suggests a role for EGFR signaling in BA pathogenesis. 相似文献60.
Ram Chandra Sangeeta Yadav Ram Naresh Bharagava 《World journal of microbiology & biotechnology》2010,26(4):685-692
This study deals with the optimization of bacterial degradation of pyridine raffinate by previously isolated two aerobic bacteria ITRCEM1 (Bacillus cereus) and ITRCEM2 (Alcaligens faecalis) with accession number DQ4335020 and DQ435021, respectively. The degradation of pyridine raffinate was studied by axenic and mixed bacterial consortium at different nutritional and environmental conditions after the removal of formaldehyde from pyridine raffinate (FPPR). Results revealed that the optimum degradation of pyridine raffinate was observed by mixed bacterial culture in presence of glucose (1% w/v) and peptone (0.2% w/v) at 20% FPPR, pH 7.0, temperature 30°C and 120 rpm at 168 h incubation period . The HPLC analysis of degraded pyridine raffinate samples has indicated the complete removal of α, β and γ picoline. Further, the GC–MS analysis of FPPR pyridine raffinate has shown the presence of pyrazine acetonitrile (6.74), 1,3-dioxepin (8.68), 2-pyridine carboxaldehyde (11.26), propiolactone (12.06), 2-butanol (13.10), benzenesulfonic acid (16.22) and 1,4-dimethyl pyperadine while phenol (17.64) and 3,4-dimethyl benzaldehyde as metabolic products of FPPR. 相似文献