全文获取类型
收费全文 | 2165篇 |
免费 | 113篇 |
国内免费 | 1篇 |
出版年
2023年 | 22篇 |
2022年 | 16篇 |
2021年 | 62篇 |
2020年 | 35篇 |
2019年 | 40篇 |
2018年 | 49篇 |
2017年 | 40篇 |
2016年 | 56篇 |
2015年 | 96篇 |
2014年 | 110篇 |
2013年 | 158篇 |
2012年 | 173篇 |
2011年 | 159篇 |
2010年 | 113篇 |
2009年 | 70篇 |
2008年 | 115篇 |
2007年 | 112篇 |
2006年 | 94篇 |
2005年 | 99篇 |
2004年 | 88篇 |
2003年 | 74篇 |
2002年 | 58篇 |
2001年 | 28篇 |
2000年 | 26篇 |
1999年 | 33篇 |
1998年 | 15篇 |
1997年 | 14篇 |
1996年 | 10篇 |
1995年 | 17篇 |
1994年 | 13篇 |
1993年 | 9篇 |
1992年 | 22篇 |
1991年 | 17篇 |
1990年 | 14篇 |
1989年 | 22篇 |
1988年 | 13篇 |
1987年 | 16篇 |
1986年 | 9篇 |
1985年 | 15篇 |
1984年 | 18篇 |
1983年 | 11篇 |
1982年 | 10篇 |
1981年 | 9篇 |
1979年 | 15篇 |
1978年 | 7篇 |
1977年 | 10篇 |
1976年 | 9篇 |
1975年 | 7篇 |
1974年 | 7篇 |
1973年 | 7篇 |
排序方式: 共有2279条查询结果,搜索用时 15 毫秒
1.
Shailesh Kumar Atma P. Dwivedi Vivek Kr. Kashyap A.K. Saxena A.K. Dwivedi Ranjana Srivastava Devi P. Sahu 《Bioorganic & medicinal chemistry letters》2013,23(8):2404-2407
Synthesis of a library of novel trans 6-methoxy-1,1-dimethyl-2-phenyl-3-aryl-2,3-dihydro-1H-inden-4-yloxy alkyl amines and their antimycobacterial activity against drug sensitive and multidrug resistant strains of Mycobacterium tuberculosis have been reported. All the new compounds in the series exhibited MIC between 1.56 and 6.25 μg/ml. Two compounds 1i and 1j with low MIC and low cytotoxicity showed significant reduction in CFU in infected mouse macrophages at 1× MIC concentration. The compound 1i inhibited the growth of M. tuberculosis in mice at 100 mg/kg dose with 1.35 log10 reduction of CFU in lungs tissue and was active against non-replicating Mycobacterium tuberculosis under anaerobic condition. 相似文献
2.
A simple and yet reliable silver impregnation method, using potassium ferrocyanide, for demonstrating nervous tissue of the rat central nervous system embedded in paraffin or paraplast is described. The method reported here is compared and discussed with earlier techniques using potassium dicyanoargentate, potassium ferrocyanide and potassium ferricyanide. 相似文献
3.
4.
5.
Madeleine St Clair Yewers Devi Stuart‐Fox Claire Alice McLean 《Ecology and evolution》2019,9(1):295-306
Space use including territoriality and spatial arrangement within a population can reveal important information on the nature, dynamics, and evolutionary maintenance of alternative strategies in color polymorphic species. Despite the prevalence of color polymorphic species as model systems in evolutionary biology, the interaction between space use and genetic structuring of morphs within populations has rarely been examined. Here, we assess the spatial and genetic structure of male throat color morphs within a population of the tawny dragon lizard, Ctenophorus decresii. Male color morphs do not differ in morphology but differ in aggressive and antipredator behaviors as well as androgen levels. Despite these behavioral and endocrine differences, we find that color morphs do not differ in territory size, with their spatial arrangement being essentially random with respect to each other. There were no differences in genetic diversity or relatedness between morphs; however, there was significant, albeit weak, genetic differentiation between morphs, which was unrelated to geographic distance between individuals. Our results indicate potential weak barriers to gene flow between some morphs, potentially due to nonrandom pre‐ or postcopulatory mate choice or postzygotic genetic incompatibilities. However, space use, spatial structure, and nonrandom mating do not appear to be primary mechanisms maintaining color polymorphism in this system, highlighting the complexity and variation in alternative strategies associated with color polymorphism. 相似文献
6.
R. Sankar P. S. Devamanoharan G. Raghupathi M. Krishnasamy C. S. Shyamala Devi 《Journal of biosciences》1987,12(3):267-271
Plumbagin was administered to rats at a concentration of 1,2,4,8 and 16 mg per kg body weight. After 24 h lipid peroxide levels
were found to decrease in subcellular fractions of liver. Plumbagin inhibited ascorbate and nicotinafde adenine dinucleotide
phosphate (reduced) dependent lipid peroxidation but was without any effect on cumene hydroperoxide dependent lipid peroxidation.
Injection of 16 mg of plumbagin per kg body weight was found to decrease liver total reduced glutathione and also fcrosomal
glucose-6-phosphatase. The results are discussed with reference to the anti- and prooxidant properties of plumbagin. 相似文献
7.
Göran Ekborg Martin Klinger Lennart Rodén John Wjesen John S Schutzbach Dee H Huang N Rama Krishna Gattadalli M Anantharamaiah 《Glycoconjugate journal》1987,4(3):255-266
3-O-β-d-Xylopyranosyl-l-serine (xylosylserine) was synthesized by the following three-step procedure: 1) 2,3,4-tri-O-benzoyl-α-d-xylopyranosyl bromide (benzobromoxylose) was condensed withN-carbobenzoxy-l-serine benzyl ester using the silver triflate-collidine complex as promoter; 2) theN-carbobenzoxy and benzyl ester groups in the resultant glycoside were cleaved by transfer hydrogenation with palladium black as catalyst and ammonium formate as hydrogen donor; and 3) the benzoyl groups were removed with methanolic ammonia. Xylosylserine was obtained in an overall yield of 70%. O-β-d-Galactopyranosyl-(1-4)-O-β-d-xylopyranosyl-(1-3)-l-serine (galactosylxylosylserine) was also synthesized by this methodology and was characterized by 2-dimensional (2D) NMR spectroscopy techniques. The two serine glycosides (xylosylserine and galactosylxylosylserine) were used in detection and partial purification of galactosyltransferase I (UDP-d-galactose:d-xylose galactosyltransferase) from adult rat liver. 相似文献
8.
Significant differences were observed in GAG metabolism of S. digitata and one of its intermediate vectors, C. quinquefasciatus. Distribution of different components such as hyaluronic acid, heparin-sulphate, chondroitin-4-sulphate, chondroitin-6-sulphate, dermatan sulphate and heparin was comparable in both. However, there were quantitative differences; the difference was marked in the activity of enzymes of GAG metabolism in presence and absence of diethylcarbamazine (DEC) a known antifilarial drug. While the activities of beta-galactosidase and beta-N-acetyl glucosaminidase of S. digitata systems showed an inhibition of 96.5 and 92.6% respectively, in the Culex systems they showed an inhibition of 93.3% and an activation of 18% respectively. The differences clearly indicate the existence of basic differences in GAG metabolism of vector and parasite. 相似文献
9.
Catabolic instability,plasmid gene deletion and recombination in Alcaligenes sp. BR60 总被引:12,自引:0,他引:12
An Alcaligenes sp. BR60, isolated from surface runoff waters of the Hyde Park industrial landfill, contained a novel 85 kb catabolic plasmid (pBR60) functional in 3-chlorobenzoate (3Cba) degradation. The plasmid exhibited a spontaneous 3.2% frequency of deletion of a 14 kb fragment specifying 3Cba degradation. The deletion mutant BR40 and mitomycin C cured strains were not able to grow on 3Cba and had reversion frequencies of less than 10-10 cell-1 generation-1. Transformation or conjugation of pBR60 into cured strains restored catabolic activity. An EcoRI, BgIII, HindIII and SaII restriction map of the deletion region was constructed, and EcoRI and HindIII fragments spanning the deletion region of the plasmid were cloned in pUC18. Conjugation of resistance plasmid R 68.45 into Alcaligenes sp. BR60, with selection on antibiotics, resulted in the elimination of pBR60 and maintenance of unaltered R68.45. In 30% of the exconjugants, 3Cba degradative capacity was retained, although variation in the regulation of 3Cba degradation was observed in these strains. Hybridization of deletion region fragments to BgIII digested total DNA of BR60 and the R68.45 cured exconjugants revealed the presence of pBR60 deletion region sequences in the chromosome of exconjugants. Hybridization also revealed a repeated sequence flanking the deletion region of pBR60. Selection on 4-chlorobenzoate as a sole source of carbon and energy resulted in the isolation of 4Cba+ mutants of Alcaligenes sp. BR60.Abbreviations 3 and 4 Cba
chlorobenzoic acid isomers and growth phenotypes
- HPLC
high pressure liquid chromatography
- ATCC
American Type Culture Collection 相似文献
10.
Summary The influence of trace elements (Co2+, Ni2+ and Fe3+) in varying concentrations and combination, was studied in 1.5 m3 Khadi & Village Industries Commission (KVIC) digesters for biogas generation from mangopeel. Addition of these trace metals enhanced the biogas yield and methane content moderately, the maximum being with the iron fed digester. The digesters were always found to be stable without much variation in total volatile fatty acids (VFA), pH, total alkalinity and other parameters. A methane content of 62% and biogas yield of 0.49 m3/kg VS added was obtained with 4000 mg/L FeCl3 supplemented mangopeel fed digester as compared to control having biogas yield of 0.22 m3/kg VS added with a methane content of about 48–50%. 相似文献