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21.
Tissue uptake of circulating hyaluronic acid 总被引:5,自引:0,他引:5
J. Robert E. Fraser Lars-Erik Appelgren Prof. Torvard C. Laurent 《Cell and tissue research》1983,233(2):285-293
Previous work in the rabbit has shown that there is a significant flux of plasma hyaluronic acid (HA) which is taken up and degraded mainly in the liver but also concentrated in the spleen. Purified 14C-labelled HA of high average molecular wt prepared by biosynthesis from D-[U-14C] glucose was injected i.v. in mice and its tissue distribution was determined by whole-body autoradiography during the next 24 h. As blood levels declined, radioactivity was concentrated in the liver and spleen as found in the rabbit, and also in bone marrow and lymph nodes. Distribution was uniform in liver tissue, concentrated and relatively persistent in the periphery of lymph nodes, and distinctly nodular within the spleen. Analysis of an aqueous liver extract taken 4 h after injection identified 14C in HA, in a macromolecular fraction resistant to fungal hyaluronidase, and in metabolites of low molecular wt. These findings confirm and extend observations based on tissue extraction in rabbits. The pattern of distribution through the body and the restricted localization within spleen and lymph nodes further suggest that HA is absorbed from plasma and tissue fluids by elements of the reticuloendothelial system. 相似文献
22.
Differential size variations between transcriptionally active and inactive telomeres of Trypanosoma brucei 总被引:19,自引:6,他引:13 下载免费PDF全文
We have studied the genes coding for the variant-specific surface antigen (VSA) in a series of seven trypanosome clones derived from AnTat 1.1: 1.1 leads to 1.3 leads to 1.6 leads to 1.16 leads to 1.1C leads to 1.3B leads to 1.18 These genes are all telomeric (1-5), and their surrounding, although sometimes similar, differs in each case. The length between these antigen genes and the corresponding DNA end appears to increase at each antigenic switch, with however occasional sharp size reductions, often linked to the involvement of the telomere in gene expression. This increase is due to a constant "growth" of the telomeres, at a rate of about 28 bp per day in at least four cases and probably linked to chromosome duplication. The telomere harbouring the transcribed VSA gene is growing slightly faster (about 36 bp per day), and it is the only one whose size reduction is progressive, leading to a terminal length heterogeneity within a clone. As a result, the active VSA gene is found in a population of telomeres which, as the trypanosomes divide, becomes increasingly heterogeneous, with however a preferred discrete size class about 1.4 kb smaller. The fact that the "active" telomere is the only one in a chromatin conformation highly sensitive to DNAaseI (1-4, 6), suggests that chromatin structure influences the rate and extent of both size increase and shortening of telomeres. 相似文献
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Conformational transitions of polynucleotides in polymer media 总被引:5,自引:0,他引:5
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Laurent Bonneau Nicole Beranger-Novat Jeannine Monin Josette Martin-Tanguy 《Plant Growth Regulation》1967,16(1):5-10
In vitro formation of roots and somatic embryos is obtained from cotyledon explants of a Spindle tree (Euonymus europaeus L.) cultured on two different media: a medium inducing callus formation and the production of roots, and a medium inducing callus formation, root and somatic embryo production. We studied the effects of -difluoromethylornithine (DFMO), a specific, irreversible inhibitor of ornithine decarboxylase (ODC) on root and somatic embryo production, growth and titers of putrescine in Euonymus explants and explant-derived calli. Early changes in putrescine levels were detected in both cultures before the visible emergence of roots or somatic embryos. DFMO rapidly inhibited putrescine accumulation and growth in non-embryogenic calli and highly stimulated rooting activity. DFMO partially inhibited putrescine accumulation in embryogenic calli. This inhibition had no effects on callus growth but significantly reduced the time of emergence of roots and highly stimulated somatic embryo production. The relationship among putrescine, putrescine metabolism, growth, root and somatic embryo formation is discussed. 相似文献
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To investigate the mechanism by which the large T antigen (T-Ag) of polyomavirus and simian virus 40 can promote recombination in mammalian cells, we analyzed homologous recombination events occurring between two defective copies of the polyomavirus middle T (pmt) oncogene lying in close proximity on the same chromosome in a rat cell line. Reconstitution of a functional pmt gene by spontaneous recombination occurred at a rate of about 2 x 10(-7) per cell generation. Introduction of the polyomavirus large T (plt) oncogene into the cell line by DNA transfection promoted recombination very efficiently, with rates in the range of 10(-1) to 10(-2) per cell generation. Recombination was independent of any amplification of viral sequences and could even be promoted by the large T-Ag from simian virus 40, which cannot activate polyomavirus DNA replication. To explain the role of large T-Ag, we propose a novel mechanism of nonconservative recombination involving slipped-strand mispairing between the two viral repeats followed by gap repair synthesis. 相似文献
28.
Ferritin H gene polymorphism in idiopathic hemochromatosis 总被引:1,自引:1,他引:0
Véronique David Panos Papadopoulos Jacqueline Yaouanq Martine Blayau Laurent Abel Elizabetta Zappone Muriel Perichon Jim Drysdale Jean-Yves Le Gall Marcel Simon 《Human genetics》1989,82(2):123-126
Summary We have analysed karyotypes and DNA from three patients with aniridia (congenital absence of irises) and Wilms' tumour. All three had constitutional deletions from the short arm of chromosome 11. The minimum region of overlap of the deletion involves a small region of band 11p13 presumed to contain the genetic loci responsible for both phenotypic abnormalities. Using cells from these patients, somatic cell hybrids with transformed mouse cells have been prepared. Individual subclones retaining either the deletion-11 chromosome or the normal chromosome 11, in addition to a variety of other human chromosomes, have been identified. The relative position of these breakpoints have been determined and the panel of hybrids has been used to map randomly-isolated 11p13 DNA sequences. The characterisation of these deletions has provided a useful panel of hybrids for random mapping strategies designed to identify the Wilms' and aniridia genes. 相似文献
29.
Inositol 1,4,5-trisphosphate (IP3) is a second messenger which induces Ca2+ release from an intracellular store. We have investigated the properties of the [32P]IP3 binding sites in rat liver. Two specific [32P]IP3 receptors with KD of 2.3 and 88 nM and respective capacities of 33 fmol/mg protein and 195 fmol/mg protein have been detected in a crude membrane fraction prepared from rat liver homogenate. The pretreatment of the liver with IP3-dependent hormones increased two-fold the capacity of the high affinity site. This effect was partly reversed by dibutyryl cyclic AMP. Permeabilized hepatocytes also displayed two [32P]IP3 binding sites with KD of 1.5 and 84 nM and respective capacities of 8 and 300 fmol/10(6) cells. We have measured the [32P]IP3 binding and the IP3-induced 45Ca2+ release in the same batch of permeabilized hepatocytes. In a low Mg2+ medium, the EC50 for 45Ca2+ release was in close correlation with the KD for the low affinity site. These data suggest that an equilibrium between two states of the IP3 receptor is regulated by hormone action and the low affinity state is responsible for the intracellular Ca2+ release. 相似文献
30.