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61.
62.
Maillet F Poinsot V André O Puech-Pagès V Haouy A Gueunier M Cromer L Giraudet D Formey D Niebel A Martinez EA Driguez H Bécard G Dénarié J 《Nature》2011,469(7328):58-63
Arbuscular mycorrhiza (AM) is a root endosymbiosis between plants and glomeromycete fungi. It is the most widespread terrestrial plant symbiosis, improving plant uptake of water and mineral nutrients. Yet, despite its crucial role in land ecosystems, molecular mechanisms leading to its formation are just beginning to be unravelled. Recent evidence suggests that AM fungi produce diffusible symbiotic signals. Here we show that Glomus intraradices secretes symbiotic signals that are a mixture of sulphated and non-sulphated simple lipochitooligosaccharides (LCOs), which stimulate formation of AM in plant species of diverse families (Fabaceae, Asteraceae and Umbelliferae). In the legume Medicago truncatula these signals stimulate root growth and branching by the symbiotic DMI signalling pathway. These findings provide a better understanding of the evolution of signalling mechanisms involved in plant root endosymbioses and will greatly facilitate their molecular dissection. They also open the way to using these natural and very active molecules in agriculture. 相似文献
63.
RNA interference allows the analysis of gene function by introducing synthetic, short interfering RNAs (siRNAs) into cells. In contrast to siRNA and microRNA duplexes generated endogenously by the RNaseIII endonuclease Dicer, synthetic siRNAs display a 5' OH group. However, to become incorporated into the RNA-induced silencing complex (RISC) and mediate target RNA cleavage, the guide strand of an siRNA needs to display a phosphate group at the 5' end. The identity of the responsible kinase has so far remained elusive. Monitoring siRNA phosphorylation, we applied a chromatographic approach that resulted in the identification of the protein hClp1 (human Clp1), a known component of both transfer RNA splicing and messenger RNA 3'-end formation machineries. Here we report that the kinase hClp1 phosphorylates and licenses synthetic siRNAs to become assembled into RISC for subsequent target RNA cleavage. More importantly, we reveal the physiological role of hClp1 as the RNA kinase that phosphorylates the 5' end of the 3' exon during human tRNA splicing, allowing the subsequent ligation of both exon halves by an unknown tRNA ligase. The investigation of this novel enzymatic activity of hClp1 in the context of mRNA 3'-end formation, where no RNA phosphorylation event has hitherto been predicted, remains a challenge for the future. 相似文献
64.
Diversity and roles of (t)RNA ligases 总被引:1,自引:1,他引:0
The discovery of discontiguous tRNA genes triggered studies dissecting the process of tRNA splicing. As a result, we have gained detailed mechanistic knowledge on enzymatic removal of tRNA introns catalyzed by endonuclease and ligase proteins. In addition to the elucidation of tRNA processing, these studies facilitated the discovery of additional functions of RNA ligases such as RNA repair and non-conventional mRNA splicing events. Recently, the identification of a new type of RNA ligases in bacteria, archaea, and humans closed a long-standing gap in the field of tRNA processing. This review summarizes past and recent findings in the field of tRNA splicing with a focus on RNA ligation as it preferentially occurs in archaea and humans. In addition to providing an integrated view of the types and phyletic distribution of RNA ligase proteins known to date, this survey also aims at highlighting known and potential accessory biological functions of RNA ligases. 相似文献
65.
Chiara Mencarelli Pilar Martinez–Martinez 《Cellular and molecular life sciences : CMLS》2013,70(2):181-203
Ceramide, the precursor of all complex sphingolipids, is a potent signaling molecule that mediates key events of cellular pathophysiology. In the nervous system, the sphingolipid metabolism has an important impact. Neurons are polarized cells and their normal functions, such as neuronal connectivity and synaptic transmission, rely on selective trafficking of molecules across plasma membrane. Sphingolipids are abundant on neural cellular membranes and represent potent regulators of brain homeostasis. Ceramide intracellular levels are fine-tuned and alteration of the sphingolipid–ceramide profile contributes to the development of age-related, neurological and neuroinflammatory diseases. The purpose of this review is to guide the reader towards a better understanding of the sphingolipid–ceramide pathway system. First, ceramide biology is presented including structure, physical properties and metabolism. Second, we describe the function of ceramide as a lipid second messenger in cell physiology. Finally, we highlight the relevance of sphingolipids and ceramide in the progression of different neurodegenerative diseases. 相似文献
66.
A. Martinez Seeber J. Polidoro A. C. Taquini Jr. 《Cellular and molecular life sciences : CMLS》1972,28(11):1317-1317
Resumen Se describe la probable existencia de presorreceptores en el ventriculo izquierdo de la rata. La vía aferente de este reflejo sería el vago y la eferente el simpático. El centro o alguna conexión neuronal estaría a nivel del bulbo raquídeo. 相似文献
67.
C Martinez R R Bernabé A de la Hera P Pereira P A Cazenave A Coutinho 《Nature》1985,317(6039):721-723
Immunoglobulin variable-region (V) genes, it is now recognized, do not encode specific receptors for T lymphocytes. Classical observations on T-cell expression of immunoglobulin idiotypes had remained unexplained until recent experiments showed that immunoglobulin idiotypes expressed by T lymphocytes in normal mice are absent in cells of the same specificity isolated from donors whose B-cell system has been suppressed by administration of anti-mu antibodies from birth. This observation provided evidence for the 'learning' of T-cell idiotypes from the B-cell/antibody system and, therefore, for the importance of idiotypic network interactions in the selection of available lymphocyte repertoires before antigenic challenge. Previously described influences of B cells and/or antibodies on the T-helper (Th) cell compartment would appear to operate at the level of clonal repertoires by complementarities with defined immunoglobulin idiotypes. Other authors, however, had previously shown the striking stability of T-cell idiotype expression in chimaeric animals reconstituted with T and B cells originating from donors showing differential idiotype expression. We have now investigated this apparent discrepancy and present here results demonstrating that immunoglobulin-dependent selection of T-cell (idiotypic) repertoires only operates for the first 3 weeks of life. 相似文献
68.
69.
R. Martinez B. Rietberg J. Skyler J. R. Oster G. O. Perez 《Cellular and molecular life sciences : CMLS》1991,47(3):270-272
Summary The effect of hyperkalemia on insulin secretion remains undefined. We evaluated portal and peripheral insulin levels in anesthetized dogs after infusions of KCl. The mean maximal increase in peripheral plasma potassium at infusion rates of 0.2 mEq/kg/h was 0.68±0.20 mEq/l. There were no significant increases in either portal or peripheral insulin levels. In contrast, in six dogs whose plasma potassium concentration increased in each case by more than 2.0 mEq/l (infusion rate of 0.5 mEq/kg/h), portal insulin levels increased fivefold (p<0.05). We conclude that only marked increases in plasma potassium concentration stimulate pancreatic insulin secretion. 相似文献
70.
Summary Equivalent spaces of42K were measured in fragments of the submandibular gland of 1-, 7-, 14- and 21-day-old and adult rats in the absence and presence of carbachol and the transport inhibitors ouabain and furosemide. The results indicate that the42K space was increased by carbachol in an ouabain-sensitive manner at all ages studied and that part of the secretagogue-stimulated K uptake occurred by way of a furosemide-sensitive transport system in the latter part of the postnatal period and in the adult. 相似文献