全文获取类型
收费全文 | 16050篇 |
免费 | 1398篇 |
国内免费 | 3篇 |
专业分类
17451篇 |
出版年
2023年 | 93篇 |
2022年 | 180篇 |
2021年 | 348篇 |
2020年 | 205篇 |
2019年 | 299篇 |
2018年 | 322篇 |
2017年 | 287篇 |
2016年 | 429篇 |
2015年 | 722篇 |
2014年 | 714篇 |
2013年 | 986篇 |
2012年 | 1119篇 |
2011年 | 1031篇 |
2010年 | 697篇 |
2009年 | 653篇 |
2008年 | 845篇 |
2007年 | 899篇 |
2006年 | 796篇 |
2005年 | 778篇 |
2004年 | 743篇 |
2003年 | 746篇 |
2002年 | 822篇 |
2001年 | 186篇 |
2000年 | 144篇 |
1999年 | 211篇 |
1998年 | 201篇 |
1997年 | 182篇 |
1996年 | 163篇 |
1995年 | 134篇 |
1994年 | 134篇 |
1993年 | 136篇 |
1992年 | 146篇 |
1991年 | 124篇 |
1990年 | 105篇 |
1989年 | 100篇 |
1988年 | 86篇 |
1987年 | 92篇 |
1986年 | 71篇 |
1985年 | 78篇 |
1984年 | 111篇 |
1983年 | 83篇 |
1982年 | 127篇 |
1981年 | 106篇 |
1980年 | 88篇 |
1979年 | 97篇 |
1978年 | 83篇 |
1977年 | 87篇 |
1976年 | 89篇 |
1975年 | 80篇 |
1973年 | 59篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
Previous studies have shown the existence of an autonomous mitochondrial GDPmannose: dolichylmonophosphate mannosyltransferase, located in mitochondiral outer membrane of liver cells. As nothing is known about glycosylation sites in mitochondria, we have investigated the topological orientation of this enzyme in intact mitochondria, using controlled proteolysis with trypsin. Mitochondria were purified sequentially by mild ultrasonic treatment and sucrose density gradient. Purity and homogeneity of mitochondrial fraction were assessed by electron microscopy and specific marker enzymes measures. Our data provide evidence for a mitochondrial GDPmannose: dolichylmonophosphate mannosyltransferase facing the cytoplasmic side of the outer membrane. However, the exposure of this enzyme to the water phase has been shown to be dependent on the ionic strength of the environment. 相似文献
52.
The partial collapse of dipolar and chemical shift tensors for peptide NH and for the amide NH at cross-link sites in cell wall peptidoglycan, of intact lyophilized cells of Aerococcus viridans, indicates NH vector root-mean-square fluctuations of 23 degrees. This result is consistent with the local mobility calculated in typical picosecond regime computer simulations of protein dynamics in the solid state. The experimental root-mean-square angular fluctuations for both types of NH vectors increase to 37 degrees for viable wet cells at 10 degrees C. The similarity in mobilities for both general protein and cell wall peptidoglycan suggests that one additional motion in wet cells involves cooperative fluctuations of segments of cell walls, attached proteins, and associated cytoplasmic proteins. 相似文献
53.
54.
Pierre J. Charest Jiro Hattori Janice DeMoor V. N. Iyer Brian L. Miki 《Plant cell reports》1990,8(11):643-646
Summary Genes coding for the enzyme acetohydroxyacid synthase, often referred to as acetolactate synthase (AHAS, ALS; EC 4.1.3.18), from wild type Arabidopsis thaliana and a sulfonylurea-resistant mutant line GH50 (csrl-1; Haughn et al. 1988) were introduced in Nicotiana tabacum. Both genes were expressed at high levels with the 35S promoter. The csrl-1 gene conferred high levels of resistance to chlorsulfuron whereas the wild type gene did not. As selectable markers, chimaeric AHAS genes yielded transgenic plants on chlorsulfuron but at much lower efficiencies than with a chimaeric neomycin phosphotransferase gene on kanamycin (Sanders et al. 1987). Shoot differentiation from leaf discs was delayed on chlorsulfuron by 4–6 weeks. This study indicated a role for mutant AHAS genes in the genetic manipulation of herbicide resistance in transgenic plants but as selectable markers for plant cells undergoing differentiation no advantage over other genes was perceived. 相似文献
55.
Medicago truncatula,a model plant for studying the molecular genetics of theRhizobium-legume symbiosis 总被引:7,自引:0,他引:7
David G. Barker Sylvie Bianchi François Blondon Yvette Dattée Gérard Duc Sadi Essad Pascal Flament Philippe Gallusci Gérard Génier Pierre Guy Xavier Muel Jacques Tourneur Jean Dénarié Thierry Huguet 《Plant Molecular Biology Reporter》1990,8(1):40-49
Medicago truncatula has all the characteristics required for a concerted analysis of nitrogen-fixing symbiosis withRhizobium using the tools of molecular biology, cellular biology and genetics.M. truncatula is a diploid and autogamous plant has a relatively small genome, and preliminary molecular analysis suggests that allelic
heterozygosity is minimal compared with the cross-fertilising tetraploid alfalfa (Medicago sativa). TheM. truncatula cultivar Jemalong is nodulated by theRhizobium meliloti strain 2011, which has already served to define many of the bacterial genes involved in symbiosis with alfalfa. A genotype
of Jemalong has been identified which can be regenerated after transformation byAgrobacterium, thus allowing the analysis ofin-vitro-modified genes in an homologous transgenic system. Finally, by virtue of the diploid, self-fertilising and genetically homogeneous
character ofM. truncatula, it should be relatively straightforward to screen for recessive mutations in symbiotic genes, to carry out genetic analysis,
and to construct an RFLP map for this plant. 相似文献
56.
57.
Jose Jacob 《Molecular and cellular biochemistry》1988,84(1):97-103
Summary Effects of Ca2+ ionophores, A23187 and lasalocid, on superoxide anion generation by chemotactic peptide, N-formyl-methionyl-leucyl-phenylalanine methyl ester, in rabbit peritoneal exudate neutrophils were studied. The ionophores by themselves did not activate superoxide anion generation in these neutrophils. When preincubated with the cells for 2 min, both the ionophores inhibited superoxide generation induced by chemotactic peptide. The inhibition was present even in the absence of extracellular Ca2+ and the inhibition was better then. Lasalocid produces a dose-dependent chlortetracycline fluorescence decrease response in neutrophils loaded with chlortetracycline. This response is independent of extracellular Ca2+ concentration and is related to release of Ca2+ from intracellular storage sites. The dose-range at which lasalocid gives this response is same as the dose-range at which it causes inhibition of superoxide response. It may be concluded that the inhibition of superoxide generation by these ionophores is correlated to intracellular Ca2+ modulation.Abbreviations FMLP
Formyl-Methionyl-Leucyl-Phenylalanine methyl ester 相似文献
58.
Christiane Levrat Dominique Ardail Renée Morelis Pierre Louisot 《Glycoconjugate journal》1988,5(4):449-466
The results reported in this paper show two distinct ways for the incorporation ofN-acetylglucosamine into mitochondrial outer membranes. The first one is the glycosylation of dolichol acceptors, which is indicated by the inhibition of the synthesis of these products by the inhibitors of the dolichol intermediates (tunicamycin and GDP). The second one is the incorporation ofN-acetylglucosamine into protein acceptors directly from UDP-N-acetylglucosamine. This second way of glycosylation is only localized in mitochondria outer membranes.The existence of a direct route forN-glycoprotein biosynthesis has been based on the following evidence. First, the synthesis of theN-acetylglucosaminylated protein acceptors was not inhibited by tunicamycin or GDP. Second, the addition of exogenous dolichol-phosphate did not change the rate of biosynthesis of glycosylated protein material. Third, the sequential incorporation ofN-acetylglucosamine and mannose from their nucleotide derivatives in the presence of GDP and tunicamycin led to the synthesis of glycosylated protein material which entirely bound to Concanavalin A-Sepharose. The oligosaccharide moiety of the glycosylated protein material resulting from the direct transfer of sugars from their nucleotide derivatives to the protein acceptor is of theN-glycan type. On sodium dodecylsulphate polyacrylamide gel electrophoresis, this glycosylated material migrated as a marker protein with a molecular weight between 45 000 and 63 000. HPLC chromatofocusing analysis revealed that the fraction studied was anionic. The oligosaccharide moiety of the glycoprotein material can only be elongated by the incorporation ofN-acetylglucosamine and galactose from their nucleotide derivatives. 相似文献
59.
Isolation and characterization of a thermophilic Methanobacterium able to use formate,the strain FTF
Jean Pierre Touzel Dominique Petroff Gloria M. Maestrojuan Gérard Prensier Guy Albagnac 《Archives of microbiology》1988,149(4):291-296
A thermophilic anaerobic which produced methane from formate and H2 and CO2 was isolated from a bench-scale digester treating a mixture of solid wastes at 55°C, after enrichment cultures on sodium acetate. The cells were slightly crooked rods occurring singly or in filaments. The bacterium was not motile, and stained Gram positive. Colonies appearing after 1 week of incubation were white with filamentous edges and 1 mm in diameter. The organism used H2:CO2 or formate as an energy source. Yeast extract was not required but stimulated growth significantly. Casamino acids were stimulatory and could serve as a nitrogen source. Cysteine was used as a sulfur source. The optimum pH for growth was 7.5. Growth occurred from 35 to 70°C with an optimum at 55°C. The deoxyribonucleic acid base composition was 49.2 mol% guanine plus cytosine. Though this isolate conforms to Methanobacterium thermoformicium, its proper assignment awaits further studies. It has been deposited in the Deutsche Sammlung von Mikroorganismen as strain DSM 3012.This work was supported in part by the Conseil Régional Nord/Pas-de-Calais 相似文献
60.
A catalogue of Clostridium thermocellum endoglucanase, β-glucosidase and xylanase genes cloned in Escherichia coli 总被引:3,自引:0,他引:3
Geoffrey P. Hazlewood Marek P.M. Romaniec Keith Davidson Olivier Grépinet Pierre Béguin Jacqueline Millet Odette Raynaud Jean-Paul Aubert 《FEMS microbiology letters》1988,51(2-3):231-236
Abstract Two independent collections of clones containing Clostridium thermocellum genes involved in cellulose have been previously obtained at IAPGR, Cambridge, and at the Pasteur Institute, Paris. The two collections were compared for cross-hybridization, restriction maps and enzyme phenotypes. Truly distinct genes were one β-glucosidase gene, two xylanase genes, and fifteen endogluconase genes. Two of the cloned fragments contained extraneous DNA which was absent from their respective counterparts isolated in the other collection. The dicrepancies resulted from in vivo rearrangements which had occurred in either of the C. thermocellum NCIB 10682 stocks used to generate the two gene banks. 相似文献