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991.
Patterns of nucleotide change in mitochondrial ribosomal RNA genes and the phylogeny of piranhas 总被引:14,自引:0,他引:14
Guillermo Ortí Paulo Petry Jorge I. R. Porto Michel Jégu Axel Meyer 《Journal of molecular evolution》1996,42(2):169-182
The patterns and rates of nucleotide substitution in mitochondrial ribosomal RNA genes are described and applied in a phylogenetic analysis of fishes of the subfamily Serrasalminae (Teleostei, Characiformes, Characidae). Fragments of 345 bp of the 12S and 535 bp of the 16S genes were sequenced for 37 taxa representing all but three genera in the subfamily. Secondary-structure models based on comparative sequence analysis were derived to characterize the pattern of change among paired and unpaired nucleotides, forming stem and loop regions, respectively. Base compositional biases were in the direction of A-rich loops and G-rich stems. Ninety-five percent of substitutions in stem regions were compensatory mutations, suggesting that selection for maintenance of base pairing is strong and that independence among characters cannot be assumed in phylogenetic analyses of stem characters. The relative rate of nucleotide substitution was similar in both fragments sequenced but higher in loop than in stem regions. In both genes, C-T transitions were the most common type of change, and overall transitions outnumbered transversions by a factor of two in 16S and four in 12S. Phylogenetic analysis of the mitochondrial DNA sequences suggests that a clade formed by the generaPiaractus, Colossoma, andMylossoma is the sister group to all other serrasalmins and that the generaMyleus, Serrasalmus, andPristobrycon are paraphyletic. A previous hypothesis concerning relationships for the serrasalmins, based on morphological evidence, is not supported by the molecular data. However, phylogenetic analysis of host-specific helminth parasites and cytogenetic data support the phylogeny of the Serrasalminae obtained in this study and provide evidence for coevolution between helminth parasites and their fish hosts. 相似文献
992.
Sophie Seigneurin-Venin Elaine Parrish Isabelle Marty François Rieger Georges Romey Michel Villaz Luis Garcia 《Experimental cell research》1996,223(2):301
The process of myoblast fusion during skeletal myogenesis is calcium regulated. Both dihydropyridine receptor and ryanodine receptor are already present on muscle precursors, at the prefusional stage, before they are required for excitation–contraction coupling. Previous pharmacological studies have shown the need for a special pool of Ca2+associated with the membrane for the fusion process to occur. We hypothesized that this pool of Ca2+is mobilized via a machinery similar to that involved in excitation–contraction coupling. The process of fusion in rat L6 muscle precursors was either totally or partially abolished in the presence of the L-type calcium channel inhibitors SR33557 and nifedipine (half inhibition towards 2 μM), respectively. The inhibition was reversible and dose-dependent. Drugs able to deplete internal calcium stores (caffeine, ryanodine, and thapsigargin) were also tested on the fusion. Both caffeine and thapsigargin drastically inhibited fusion whereas ryanodine had no effect. This suggests that fusion may be controlled by internal pools of Ca2+but that its regulation may be insensitive to ryanodine. We presumed that an early form of the ryanodine receptor may exist, with different pharmacological properties than the adult forms. Indeed, Western blot analysis of pre- and postfusional L6 cells demonstrated the presence, at the prefusional stage, of a transient form of the ryanodine receptor protein with an apparent molecular weight slightly different from those of the classical skeletal and cardiac forms. Taken together, these results support the hypothesis that the fusion process is driven by a mechanism involving both the dihydropyridine receptor (α1 subunit of the L-type Ca2+channel) and the internal stores of Ca2+. The machinery underlying this mechanism might consist of slightly different forms of the classic molecules that in adult muscle ensure excitation–contraction coupling. It remains to be seen, however, whether the mobilization of the internal pool of Ca2+is triggered by the type of mechanism already described in skeletal muscle. 相似文献
993.
Agents known to influence Ca2+ homeostasis affected significantly the vegetative growth and starvation-induced conidiation ofTrichoderma viride. Ca2+ in millimolar concentrations stimulated both growth and conidiation; a Ca2+ deprivation of the fungus by the chelation of extracellular Ca2+ (not Mg2+ or divalent trace metals) with EGTA (ethyleneglycolbis(2-aminoethylether)-N,N,N′,N′-tetraacetic acid) restricted both the
vegetative growth rate and starvation-induced conidiation. Both processes were affected by either Ca2+ or EGTA with different efficiencies. Divalent cations (Sr2+, Ba2+, Co2+, Ni2+, Mg2+, Cd2+, Cu2+, Mn2+) and La3+ (inorganic Ca2+ blockers) in millimolar concentrations exerted complex (stimulatory, inhibitory, or biphasic) effects on growth and conidiation.
In general, their effects on the two processes were mutually different either qualitatively, or quantitatively, or both. Organic
Ca2+ antagonists (verapamil and dihydropyridines) inhibited the vegetative growth. The results show that Ca2+ is required for vegetative growth and conidiation, and that different Ca2+-dependent mechanisms may be involved in the two processes. Divalent cations could serve as a tool for investigating the relationship
between growth and conidiation. 相似文献
994.
H. Mönkemann U. Hölker O. Golubnitchaya-Labudová H. Lichtenberg-Fraté M. Höfer 《Folia microbiologica》1996,41(5):445-448
We describe an evidence for the existence of a ligninase isoenzyme H8 in the deuteromyceteFusarium oxysporum on the genomic as well as on the RNA level. 相似文献
995.
The chromosomes of the European eel Anguilla anguilla have been analyzed with a replication banding technique from lymphocyte cultures treated with 5-BrdU. This technique allows us to identify with high resolution the individual chromosome pairs and to differentiate classes of chromatin by the order of replication. The replication banding obtained on the chromosomes of European eel can be related with the structural bands described in this species. 相似文献
996.
An analysis of the effects of inbreeding on the genetic structure of a colonizing population of Drosophila subobscura has been carried out. Species of Drosophila, particularly D. subobscura, may have lethal alleles associated with chromosomal inversions and our aim was to assess the extent to which the genome is balanced in this way. The frequencies of chromosomal inversions were compared between a large population and a set of 72 lines that were maintained by brother-sister mating for 10 generations. Fisher's matrix method was used to calculate the expected homozygosity in these inbred lines for 5 allozyme loci (Aph, Hk-1, Lap, Odh, and Pept-1) used as markers of large chromosomal segments. Furthermore, the expected rates of fixation corresponding to these allozyme loci were also calculated. The results show that the amount of homozygosis observed did not differ significantly from expectations (with the corresponding loss of lines as a consequence of the reduction in viability). However, two deviations from strict neutrality were observed: there was a heterozygote excess at the Lap locus, and the frequency of the O
5 inversion (always associated with a lethal gene in colonizing populations) was higher than expected. 相似文献
997.
Three fluorescent probes, tetramethyl rhodamine ethyl ester (TMRE), 3,3′-dipropylthiacarbocyanine iodide (diS-C3(3)) and 3,3′-dipropyloxacarbocyanine iodide (diO-C3(3)), were tested for their suitability as fluorescent indicators of membrane potential inSaccharomyces cerevisiœ in studies performed by flow cytometry. For all these dyes the intensity of fluorescence of stained cells increased with
probe concentration in the range of 60–3000 nmol/L. The optimum staining period was 15–20 min for diS-C3(3). Depolarization of cells by increased extracellular potassium level and by valinomycin elicited with all probes a drop
in fluorescence intensity. In some yeast batches this depolarization was accompanied by a separation of subpopulations with
different fluorescence properties. 相似文献
998.
Vanadate (NaVO3) in concentrations between 0.1–3.0 mmol/L inhibited the production of secondary metabolites (SMs) of strains of the following
species:Trichoderma viride, Penicillium purpurogenum, Penicillium citrinum, Talaromyces avellaneus, andVerticillium psalliotœ. Growth was either not affected by NaVO3, or the inhibition of the SM production occurred at lower NaVO3, concentrations than that of the growth. Thus, at some NaVO3 concentration the SM production was inhibited but the growth remained unaffected. The results suggest that NaVO3 exerts a specific action either on the SM biosynthetic pathway(s) or on the export of SMs from cells. 相似文献
999.
The effects of subinhibitory concentrations (1/4, 1/8, 1/16 of the MIC) of quinolones (ciprofloxacin, enoxacin, nalidixic
acid, norfloxacin, ofloxacin, pefloxacin), aminoglycosides (amikacin, gentamicin, netilmicin, streptomycin, tobramycin), β-lactams
(aztreonam, ceftazidime, imipenem, ticarcilin) and macrolides (erythromycin, roxitromycin) on the excretion of alginate by
aP. aeruginosa strain were studied. Both β-lactam and macrolide antibiotics were found ineffective at the concentrations tested, except
erythromycin and imipenem at 1/4 MIC. Aminoglycosides at a concentration of 1/4 MIC reduced most effectively the excretion
of alginate. Quinolones were also effective at this sub-MIC; 1/16 MIC was ineffective with all antibiotics or stimulated the
production of alginate. 相似文献
1000.
González Mariela Montoya Rolando Candia Arturo Gómez Patricia Cisternas Manuel 《Hydrobiologia》1996,326(1):229-234
The extreme phenotypic variability recognized among the species of Gracilaria has highlighted the need for the application of refined methods to help solve taxa identifications. In Chile, there still exists uncertainty about the exact number of Gracilaria species. Our investigations are centered on DNA analyses of morphotypes collected from different geographical locations, namely Lenga and Isla Santa María, Region VIII (36°00 S to 38°00 S), and Maullín, Region X (39°30 S to 43°40 S). These two regions of Chile are considered as areas of confluence of G. chilensis, G. verrucosa, and a species of Gracilariopsis. In this study four morphotypes, from a natural bed located in Maullín, were analyzed for RFLP of plastid DNA and the results compared with data of four morphotypes from a bed in Lenga. The DNA banding patterns from each enzyme digest were identical irrespective of morphotypes and/or locations. In an attempt to unravel the nature of the morphological differences found among Lenga and Maullín morphotypes, RAPD analyses of nuclear DNA were also performed; however, no polymorphism has been found yet. Therefore, the data of this study, as well as concurrent data from preliminary interfertility tests, suggest that all morphotypes belong to a single taxon, Gracilaria chilensis.Departamento de Botánica, Facultad de Ciencias Naturales y Oceanográficas 相似文献