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991.
Haloarchaeal flagella are composed of a number of distinct flagellin proteins, specified by genes in two separate operons (A and B). The roles of these flagellins were assessed by studying mutants of H. salinarum with insertions in either the A or the B operon. Cells of the flgA- mutant produced abnormally short, curved flagella that were distributed all over the cell surface. The flgA2- strain produced straight flagella, mainly found at the poles. The flgB- mutant had flagella of the same size and spiral shape as wild-type cells, but these cells also showed unusual outgrowths, which appeared to be sacs filled with basal body-like structures. In broth cultures of this mutant, the medium accumulated flagella with basal body-like structures at their ends. 相似文献
992.
993.
Sun JP Wu L Fedorov AA Almo SC Zhang ZY 《The Journal of biological chemistry》2003,278(35):33392-33399
The pathogenic bacteria Yersinia are causative agents in human diseases ranging from gastrointestinal syndromes to bubonic plague. There is increasing risk of misuse of infectious agents, such as Yersinia pestis, as weapons of terror as well as instruments of warfare for mass destruction. Because the phosphatase activity of the Yersinia protein tyrosine phosphatase, YopH, is essential for virulence in the Yersinia pathogen, potent and selective YopH inhibitors are expected to serve as novel anti-plague agents. We have identified a specific YopH small molecule inhibitor, p-nitrocatechol sulfate (pNCS), which exhibits a Ki value of 25 microM for YopH and displays a 13-60-fold selectivity in favor of YopH against a panel of mammalian PTPs. To facilitate the understanding of the underlying molecular basis for tight binding and specificity, we have determined the crystal structure of YopH in complex with pNCS at a 2.0-A resolution. The structural data are corroborated by results from kinetic analyses of the interactions of YopH and its site-directed mutants with pNCS. The results show that while the interactions of the sulfuryl moiety and the phenyl ring with the YopH active site contribute to pNCS binding affinity, additional interactions of the hydroxyl and nitro groups in pNCS with Asp-356, Gln-357, Arg-404, and Gln-446 are responsible for the increased potency and selectivity. In particular, we note that residues Arg-404, Glu-290, Asp-356, and a bound water (WAT185) participate in a unique H-bonding network with the hydroxyl group ortho to the sulfuryl moiety, which may be exploited to design more potent and specific YopH inhibitors. 相似文献
994.
Amar P Ballet P Barlovatz-Meimon G Benecke A Bernot G Bouligand Y Bourguine P Delaplace F Delosme JM Demarty M Fishov I Fourmentin-Guilbert J Fralick J Giavitto JL Gleyse B Godin C Incitti R Képès F Lange C Le Sceller L Loutellier C Michel O Molina F Monnier C Natowicz R Norris V Orange N Pollard H Raine D Ripoll C Rouviere-Yaniv J Saier M Soler P Tambourin P Thellier M Tracqui P Ussery D Vincent JC Vannier JP Wiggins P Zemirline A 《Acta biotheoretica》2002,50(4):357-373
995.
Fedorov VB Stenseth NC 《Proceedings. Biological sciences / The Royal Society》2002,269(1505):2071-2077
Cryptic northern refugia beyond the ice limit of the Pleistocene glaciations may have had significant influence on the current pattern of biodiversity in Arctic regions. In order to evaluate whether northern glacial refugia existed in the Canadian Arctic, we examined mitochondrial DNA phylogeography in the northernmost species of rodents, the collared lemming (Dicrostonyx groenlandicus) sampled across its range of distribution in the North American Arctic and Greenland. The division of the collared lemming into the Canadian Arctic and eastern Beringia phylogroups does not support postglacial colonization of the North American Arctic from a single eastern Beringia refugium. Rather, the phylogeographical structure and sparse fossil records indicate that, during the last glaciation, some biologically significant refugia and important sources of postglacial colonization were located to the northwest of the main ice sheet in the Canadian Arctic. 相似文献
996.
Bacterivory by heterotrophic flagellates: community structure and feeding strategies 总被引:4,自引:0,他引:4
Heterotrophic flagellates (HF) are known as most important grazers of bacteria in many aquatic ecosystem. HF cannot be treated
as a black box since HF generally contain a diverse community of species significantly differing in their feeding behaviour
and other ecological properties. Today it seems that the dominant taxonomic groups among heterotrophic nano- and microflagellate
communities within different marine, brackish and limnetic pelagic communities (heterokont taxa, dinoflagellates, choanoflagellates,
kathablepharids) and benthic communities (euglenids, bodonids, thaumatomonads, apusomonads, cercomonads) are relatively similar.
HF among protista incertae sedis, often neglected in ecological studies, are abundant bacterivores in all investigated habitats. Recent studies of flagellate
feeding processes indicated that there are significant species-specific differences and individual variability regarding the
food uptake and food selection of bacterivorous flagellates: Variability of bacterivory is discussed regarding the prevailing
feeding modes, the energy budgets, the considerable importance of slight deviations in the time budgets of feeding phases,
the ingestion rates and the feeding microhabitat, respectively. The significant flexibility of the grazing impact of bacterivorous
flagellate communities creates a complex top-down pressure on bacteria which should have lead to the evolution of efficient
predator avoidance mechanisms in bacteria and should be at least partly responsible for the diversity of present bacteria.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
997.
Christoph Krafft Ferdinand von Eggeling Orlando Guntinas‐Lichius Arndt Hartmann Maximilian J. Waldner Markus F. Neurath Jürgen Popp 《Journal of biophotonics》2018,11(1)
It is pivotal for medical applications, such as noninvasive histopathologic characterization of tissue, to realize label‐free and molecule‐specific representation of morphologic and biochemical composition in real‐time with subcellular spatial resolution. This unmet clinical need requires new approaches for rapid and reliable real‐time assessment of pathologies to complement established diagnostic tools. Photonic imaging combined with digitalization offers the potential to provide the clinician the requested information both under in vivo and ex vivo conditions. This report summarizes photonic approaches and their use in combination with image processing, machine learning and augmented virtual reality that might solve current challenges in modern medicine. Details are given for pathology, intraoperative diagnosis in head and neck cancer and endoscopic diagnosis in gastroenterology. 相似文献
998.
Lambda phage cro repressor interaction with its operator DNA: 2'-deoxy-5-fluorouracil OR3 analogues 总被引:2,自引:0,他引:2
The experiments here show that chemically synthesized DNA containing fluorine at selected sites can be used to test specific predictions of a model for cro repressor--operator interaction. This is done by observation of the perturbation to the fluorine-19 NMR spectra of analogues of OR3 synthesized with 2'-deoxy-5-fluorouracil at specific positions in the DNA helix. Although the three-dimensional structure of the cro repressor from phage lambda has been determined by Matthews and co-workers [Anderson, W., Ohlendorf, D., Takeda, Y., & Matthews, B. (1981) Nature (London) 290, 754-758], direct structural observations on the complex of the protein with its specific DNA recognition sequence, OR3, are limited. From that structure of the protein, alone, a model of its complex to DNA was built by fitting B-form DNA, with some distortion [Ohlendorf, D., Anderson, W., Fisher, R., Takeda, Y., & Matthews, B. (1982) Nature (London) 298, 718-723]. That model proposes that the cro repressor contacts only one side of this DNA double helix and a number of specific protein--DNA contacts. To test the model, 2'-deoxy-5-fluorouracil was used to place the fluorine-19 nuclear spin-label on the side of the DNA contacting the cro repressor and on the opposite side facing away from the cro repressor. The results presented here are consistent with the prediction that lambda phage cro repressor contacts only one side of the DNA double helix. 相似文献
999.
On the basis of DNA from a beta-thalassemic patient, human gene library has been obtained using bacteriophage lambda EMBL4 as a vector. The recombinants contain human DNA insertions of 15 to 20 kb. The lambda A1 beta 1 clone has been isolated by the method of hybridization of phage plaque replicas to the HhaI fragment of JW102 plasmid containing human beta-globin cDNA. Restriction mapping revealed the presence of a 22 kb human DNA fragment comprising a portion of the beta-globin gene system. Subcloned fragments of beta-globin gene (within the pUC19 plasmid or phage MI3mp10) were sequenced using the Maxam and Gilbert method as well as that of Sanger. 2150 nucleotides in total were analysed. We have detected the point substitution G----A in the 110 nucleotide of minor intron, leading to the formation of an additional splicing site. 相似文献
1000.
V F Fedorov V N Zozulia T L Piatigorskaia V A Chernov Iu P Blago? 《Molekuliarnaia biologiia》1989,23(5):1440-1446
By the methods of heat denaturation and luminescence the interaction between an antitumor drug prospidine and DNA in aqueous solutions at two ionic strengths (0.1 and 0.001 M NaCl) and at various prospidine concentrations was studied. For the first time it has been demonstrated that the interaction occurs at 0.1 M NaCl and therapeutic prospidine concentrations. In the framework of Frank-Kamenetsky's theory of melting of a polymer with stabilizing ligands the size of the binding site and binding constants (K) with the decrease of ionic strength, the lack of alterations in the DNA UV absorption spectrum on complex formation and the data on the competitive binding of ethydium bromide suggest that at the first stage of the reaction an external complex is formed due to electrostatic interactions between quaternary nitrogen atoms of prospidine and DNA phosphate groups. Incubation of the complex at 37 0 C leads to a decrease of the DNA melting temperature and hyperchromic effect. Presumably this is due to the relatively slow formation of chemical bonds between alkylating groups of prospidine and nucleophilic groups of DNA bases, which results in the destabilization and denaturation of DNA. It is concluded that the interaction between prospidine and DNA must be taken into consideration when studying the molecular mechanism of prospidine antitumour activity. 相似文献