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81.
Anna-Maria M. Schmid 《Protoplasma》1994,181(1-4):43-60
Summary Aspects of morphogenesis and morphology of diatom cell walls are reviewed to highlight functional correlations between wall structures and three-dimensional cytoplasmic activities during the cell cycle. Morphogenesis of the siliceous valve within the silica deposition vesicle is discussed in the light of the dependency on a precisely orchestrated moulding machinery, involving the cytoskeleton, mitochondria, endoplasmic reticulum, spacer vesicles produced by the Golgi apparatus, and the plasmalemma, in combination with adhesion of the cells to parts of the parental wall and localized plasmolyses. Sensitivity of morphogenetic events to fluctuations of external factors has implications for taxonomy.Abbreviations CF
cleavage furrows
- cPL
cleavage plasmalemma
- GB
girdle bands
- LP
labiate process
- LPA
labiate process apparatus
- MC
microtubule center
- mLP
macro labiate process
- MT
microtubule
- MTOC
microtubules organizing center
- PL
plasmalemma
- SDV
silica deposition vesicle
- SL SDV
membrane
- SpV
spacer vesicles
Dedicated to Professor Peter Sitte on the occasion of his 65th birthday 相似文献
82.
83.
Role of the Cys 2-Cys 10 disulfide bond for the structure, stability, and folding kinetics of ribonuclease T1. 总被引:2,自引:0,他引:2 下载免费PDF全文
L. M. Mayr D. Willbold O. Landt F. X. Schmid 《Protein science : a publication of the Protein Society》1994,3(2):227-239
The Cys 2-Cys 10 disulfide bond in ribonuclease T1 was broken by substituting Cys 2 and Cys 10 by Ser and Asn, respectively, as present in ribonuclease F1. This C2S/C10N variant resembles the wild-type protein in structure and in catalytic activity. Minor structural changes were observed by 2-dimensional NMR in the local environment of the substituted amino acids only. The thermodynamic stability of ribonuclease T1 is strongly reduced by breaking the Cys 2-Cys 10 bond, and the free energy of denaturation is decreased by about 10 kJ/mol. The folding mechanism is not affected, and the trans to cis isomerizations of Pro 39 and Pro 55 are still the rate-limiting steps of the folding process. The differences in the time courses of unfolding and refolding are correlated with the decrease in stability: the folding kinetics of the wild-type protein and the C2S/C10N variant become indistinguishable when they are compared under conditions of identical stability. Apparently, the Cys 2-Cys 10 disulfide bond is important for the stability but not for the folding mechanism of ribonuclease T1. The breaking of this bond has the same effect on stability and folding kinetics as adding 1 M guanidinium chloride to the wild-type protein. 相似文献
84.
Molecular characterization of ura1, a mutant allele for orotidine-5'-monophosphate decarboxylase in Schizophyllum commune 总被引:1,自引:0,他引:1
Abstract The basis of the auxotrophic ural phenotype in Schizophyllum commune has been investigated. Two point mutations causing changes in conserved amino acid positions 62 (from lysine to glutamate) and 79 (from leucine to phenylalanine) most likely are the cause for the observed phenotype, whereas the overall gene structure was unchanged. Since reversion rates in this locus are extremely low, a single point mutation could not be expected to be the cause for the mutation. Besides the two point mutations expected to be induced by UV mutagenesis, the two alleles investigated from independently isolated strains differ by approximately 7% in nucleic acid sequence and about 3% in amino acid sequence, indicating a distant relationship between the strains used. 相似文献
85.
Metabolism of 2,2'-dihydroxybiphenyl by Pseudomonas sp. strain HBP1: production and consumption of 2,2',3-trihydroxybiphenyl. 总被引:3,自引:2,他引:1 下载免费PDF全文
Cells of Pseudomonas sp. strain HBP1 grown on 2-hydroxy- or 2,2'-dihydroxybiphenyl contain NADH-dependent monooxygenase activity that hydroxylates 2,2'-dihydroxybiphenyl. The product of this reaction was identified as 2,2',3-trihydroxybiphenyl by 1H nuclear magnetic resonance and mass spectrometry. Furthermore, the monooxygenase activity also hydroxylates 2,2',3-trihydroxybiphenyl at the C-3' position, yielding 2,2',3,3'-tetrahydroxybiphenyl as a product. An estradiol ring cleavage dioxygenase activity that acts on both 2,2',3-tri- and 2,2',3,3'-tetrahydroxybiphenyl was partially purified. Both substrates yielded yellow meta-cleavage compounds that were identified as 2-hydroxy-6-(2-hydroxyphenyl)-6-oxo-2,4-hexadienoic acid and 2-hydroxy-6-(2,3-dihydroxyphenyl)-6-oxo-2,4-hexadienoic acid, respectively, by gas chromatography-mass spectrometry analysis of their respective trimethylsilyl derivatives. The meta-cleavage products were not stable in aqueous incubation mixtures but gave rise to their cyclization products, 3-(chroman-4-on-2-yl)pyruvate and 3-(8-hydroxychroman-4-on-2-yl)pyruvate, respectively. In contrast to the meta-cleavage compounds, which were turned over to salicylic acid and 2,3-dihydroxybenzoic acid, the cyclization products are not substrates to the meta-cleavage product hydrolase activity. NADH-dependent salicylate monooxygenase activity catalyzed the conversions of salicylic acid and 2,3-dihydroxybenzoic acid to catechol and pyrogallol, respectively. The partially purified estradiol ring cleavage dioxygenase activity that acted on the hydroxybiphenyls also produced 2-hydroxymuconic semialdehyde and 2-hydroxymuconic acid from catechol and pyrogallol, respectively. 相似文献
86.
Two blue-light responses of Phaeophyta that are expressed within a few seconds of a blue-light stimulus were characterized with respect to their photoreception properties. The first response is the activation of red-light-saturated photosynthesis which can be stimulated to values up to 5 times the rates in red light, depending on the species. The second response is a blue-light-induced acidification measurable at the plant surface. Both responses have similar kinetic characteristics and thus led us initially to hypothesise that they were causally connected in the same transduction mechanism. The two responses have action spectra [measured for Ectocarpus siliculosus (Dillwyn) Lyngb. and Laminaria saccharina (L.) Lamouroux] that are indistinguishable within the relatively large limits of error. However, in all species tested, the threshold sensitivity for blue light of the photosynthetic response is lower than that of the pH-shift by a factor of 2 to 150. Furthermore, stimulation of photosynthesis is sensitive to the flavin inhibitors, KI and phenylacetic acid, but the pH response is not affected by these inhibitors. Thus, the blue-light-induced pH-shift does not cause the stimulation of photosynthesis. In contrast, the different fluence-response relationships of the two responses and particularly the differential effect of the inhibitors are clear evidence for the action of two independent transduction pathways and photoreceptor systems for blue light. At least photoreception for stimulation of photosynthesis involves a flavin-or and a pterin.Abbreviations DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- PAA
phenylacetic acid
We thank Dr. C. A. Maggs for collecting P. pavonica. This research was supported by National Environment Research Council grant No. GR3/8102. 相似文献
87.
The DNA sequence of the wild type S. typhimurium parE gene was determined. The predicted protein has 96.7% amino acid identity with the ParE protein of E.coli, but is 29 amino acids longer, due to an additional basepair in the 3' end of the S. typhimurium gene. Subclones of the S. typhimurium parE gene localized the sites of four heat sensitive mutations within parE. The parE206 and parE374 mutations are identical (Val67-Met) and lie in a highly conserved region corresponding to the ATP binding pocket of GyrB. Two additional heat sensitive mutations were sequenced and predict the following amino acid substitutions: parE377 (Gly399-Ser) and parE493 (Thr583-Pro). All of the heat sensitive mutations lie in regions with strong amino acid homology to GyrB. 相似文献
88.
David W. Kikuchi William L. Allen Kevin Arbuckle Thomas G. Aubier Emmanuelle S. Briolat Emily R. Burdfield-Steel Karen L. Cheney Klára Daňková Marianne Elias Liisa Hämäläinen Marie E. Herberstein Thomas J. Hossie Mathieu Joron Krushnamegh Kunte Brian C. Leavell Carita Lindstedt Ugo Lorioux-Chevalier Melanie McClure Callum F. McLellan Iliana Medina Viraj Nawge Erika Páez Arka Pal Stano Pekár Olivier Penacchio Jan Raška Tom Reader Bibiana Rojas Katja H. Rönkä Daniela C. Rößler Candy Rowe Hannah M. Rowland Arlety Roy Kaitlin A. Schaal Thomas N. Sherratt John Skelhorn Hannah R. Smart Ted Stankowich Amanda M. Stefan Kyle Summers Christopher H. Taylor Rose Thorogood Kate Umbers Anne E. Winters Justin Yeager Alice Exnerová 《Journal of evolutionary biology》2023,36(7):975-991
Prey seldom rely on a single type of antipredator defence, often using multiple defences to avoid predation. In many cases, selection in different contexts may favour the evolution of multiple defences in a prey. However, a prey may use multiple defences to protect itself during a single predator encounter. Such “defence portfolios” that defend prey against a single instance of predation are distributed across and within successive stages of the predation sequence (encounter, detection, identification, approach (attack), subjugation and consumption). We contend that at present, our understanding of defence portfolio evolution is incomplete, and seen from the fragmentary perspective of specific sensory systems (e.g., visual) or specific types of defences (especially aposematism). In this review, we aim to build a comprehensive framework for conceptualizing the evolution of multiple prey defences, beginning with hypotheses for the evolution of multiple defences in general, and defence portfolios in particular. We then examine idealized models of resource trade-offs and functional interactions between traits, along with evidence supporting them. We find that defence portfolios are constrained by resource allocation to other aspects of life history, as well as functional incompatibilities between different defences. We also find that selection is likely to favour combinations of defences that have synergistic effects on predator behaviour and prey survival. Next, we examine specific aspects of prey ecology, genetics and development, and predator cognition that modify the predictions of current hypotheses or introduce competing hypotheses. We outline schema for gathering data on the distribution of prey defences across species and geography, determining how multiple defences are produced, and testing the proximate mechanisms by which multiple prey defences impact predator behaviour. Adopting these approaches will strengthen our understanding of multiple defensive strategies. 相似文献
89.
Recruitment of epidermal growth factor and transferrin receptors into coated pits in vitro: differing biochemical requirements. 总被引:10,自引:1,他引:9 下载免费PDF全文
The biochemical requirements for epidermal growth factor (EGF) and transferrin receptor-mediated endocytosis were compared using perforated human A431 cells. Morphological studies showed that horseradish peroxidase (HRP)-conjugated EGF and gold-labeled antitransferrin (Tfn) receptor antibodies were colocalized during endocytosis in vitro. The sequestration of both ligands into deeply invaginated coated pits required ATP hydrolysis and cytosolic factors and was inhibited by GTP gamma S, indicating mechanistic similarities. Importantly, several differences in the biochemical requirements for sequestration of EGF and Tfn were also detected. These included differing requirements for soluble AP (clathrin assembly protein) complexes, differing cytosolic requirements, and differing sensitivities to the tyrosine kinase inhibitor, genistein. The biochemical differences detected between EGF and Tfn sequestration most likely reflect specific requirements for the recruitment of EGF-receptors (R) into coated pits. This assay provides a novel means to identify the molecular bases for these biochemical distinctions and to elucidate the mechanisms involved in ligand-induced recruitment of EGF-R into coated pits. 相似文献
90.
Jörg Schmid Peter Möller Gerd Moldenhauer Bernd Dörken Heiner Bihl Siegfried Matzku 《Cancer immunology, immunotherapy : CII》1993,36(4):274-280
Accumulation of radiolabelled monoclonal antibodies (mAb) in human B-lymphoma xenografts was found to result in two distinct patterns. The basic elements leading to these patterns were elucidated by autoradiographic and immunohistological analysis applied to the nude mouse xenografts BJAB and OCI.LY1. With BJAB, accumulation occurred exclusively in peripheral cell layers of the lymphoma nodule, while central areas were not accessible irrespective of mAb dose. This feature was the consequence of an inefficient transport across intratumoral vessels together with peripheral mAb supply through a subcapsular pseudosinus. With OCI.LY1, intratumoral vessels showed generalized leakiness. Furthermore, interstitial transport was operative to a fair extent, such that in early images multiple sites of mAb extravasation were obvious, which coalesced during the course of prolonged uptake. The pattern of peripheral mAb uptake resulted in a low overall tumour uptake, while multifocal uptake yielded substantial accumulation values. 相似文献