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1.
L. N. GILLMAN D. J. KEELING R. C. GARDNER S. D. WRIGHT 《Journal of evolutionary biology》2010,23(6):1327-1330
A faster rate of nuclear DNA evolution has recently been found for plants occupying warmer low latitudes relative to those in cooler high latitudes. That earlier study by our research group compared substitution rates within the variable internal transcribed spacer (ITS) region of the ribosomal gene complex amongst 45 congeneric species pairs, each member of which differed in their latitudinal distributions. To determine whether this rate differential might also occur within highly conserved DNA, we sequenced the 18S ribosomal gene in the same 45 pairs of plants. We found that the rate of evolution in 18S was 51% faster in the tropical plant species relative to their temperate sisters and that the substitution rate in 18S correlated positively with that in the more variable ITS. This result, with a gene coding for ribosomal structure, suggests that climatic influences on evolution extend to functionally important regions of the genome. 相似文献
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C-Type Virus Released from Cultured Human Rhabdomyosarcoma Cells 总被引:44,自引:0,他引:44
R. M. McALLISTER M. NICOLSON M. B. GARDNER R. W. RONGEY S. RASHEED P. S. SARMA R. J. HUEBNER M. HATANAKA S. OROSZLAN R. V. GILDEN A. KABIGTING L. VERNON 《Nature: New biology》1972,235(53):3-6
RD-114 virus, released from human rhabdomyosarcoma cells, has all the characteristics of a mammalian C-type virus. Immunological tests indicate that it differs from all known C-type viruses and is the most likely candidate for a human C-type virus yet described. 相似文献
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T. R. FRASIER T. RASTOGI M. W. BROWN P. K. HAMILTON S. D. KRAUS B. N. WHITE 《Molecular ecology resources》2006,6(4):1025-1029
A North Atlantic right whale (Eubalaena glacialis) genomic library was developed and screened with a (GATA)8 probe to identify tetranucleotide microsatellite loci. Sixteen characterized loci were polymorphic in North Atlantic and/or South Atlantic (Eubalaena australis) right whales, 12 being polymorphic in E. glacialis, and 15 in E. australis. Fourteen of these were combined with 21 other previously identified loci for a suite of 35 loci which can be used to increase resolution of genetic analyses of these species. Multiplex reactions were developed for genotyping samples at these loci, providing a method that is rapid, reliable and cost‐effective. 相似文献
6.
Nitrogen (N) mineralization rates and the temperature response patterns of mineral N production in surface (0–7.6 cm) soils were compared in laboratory incubation studies based on disturbed, composite samples. Seasonal variation in the field levels of mineral N, and mineralization potential of intact (7.6 × 5.6 cm diameter) soil cores, were also investigated. Ammonification proceeded rapidly in each soil. Nitrification did not occur in grassy forest (GF) soil but was active in both layered forest (LF) and mossy forest (MF) soils, especially the former. Total mineral N production was greatest in MF and least in LF. Ammonification in disturbed samples was maximal at 50°C in all three soils with a secondary peak at 10°C in LF soil. Nitrification in LF and MF soils was most rapid at 25°C. Several species of ammonifying bacteria with different temperature optima were isolated, indicating that the process of ammonification is a composite of the activities of a variety of decomposer microbes. Mean field levels of mineral N and NH4–N throughout the year were greatest in MF and least in LF. Seasonal fluctuations in NH4–N were evident, concentrations being universally low in mid-winter (about 1.5 μgg-1), increasing to a maximum in late summer (about 5 μg g-1 in LF: 16–18 μg g-1 in GF and MF). Field levels of NO3–N were more constant and never more than 5 μg g-1 in any community. Both total mineralization and ammonification in intact cores were greatest in MF and least in LF while nitrification was greatest in LF and almost negligible in GF, thus confirming the results obtained with disturbed samples. The potential for mineralization was large in mid-winter when the amount of mineral N was very low, and small in late summer when field levels were higher: this is interpreted as indicating that seasonal climatic factors regulate the availability of substrates for decomposers. Spatial variability in field levels of mineral N and mineral N production in the laboratory was evidenced by significant ‘sampling site’ effects in each community: however, at the sampling intensity used, the presence of bark mounds around Eucalyptus saligna trees could not be shown to affect these attributes. The inability of GF soil to nitrify when incubated in the laboratory could not be ascribed to a high C/N ratio, low pH, lack of substrate ammonium, or a low population of autotrophic nitrifying bacteria. No attempt was made to investigate the presence of allelopathic nitrification inhibitors. No evidence was obtained to support the view that nitrification is atypical of climax communities in situ. The most productive forest (LF) had the greatest capacity to nitrify and the least productive community (GF) the smallest capacity to do so. 相似文献
7.
SCOTT LYELL GARDNER 《Zoological Journal of the Linnean Society》1991,102(2):169-201
Coevolution was studied in six species of rodents of the genus Ctenomys and their parasitic nematodes of the genus Paraspidodera , collected in Bolivia. Representatives of the families Octodontidae and Caviidae were used as outgroups for the mammals, and nematodes from caviids were used as outgroups of the nematodes from ctenomyids. For the nematodes, quantitative and qualitative morphological characteristics of both males and females and electrophoretic characters of both sexes were used to generate phylogenetic hypotheses of evolutionary relationships of the OTUs occurring in hosts of different species. Concordance estimates of cladograms generated from biochemical—genetic and morphological data of the nematodes show a percentage incongruence (Mickevich-Farris Incongruence Statistic or I MF ) of 8.23% in the character sets. Parsimony mapping, testing concordance of topologies between the trees derived from both analysis of both morphological and biochemical—genetic data indicates an overall agreement of 82.3°. Comparisons of topologies of the host and parasite cladograms, as measured with parsimony mapping, showed 70.8% concordance, indicating substantially more cospeciation than host-switching in the Ctenomys-Paraspidodera host-parasite system. Nematodes of the genus Paraspidodera appear to have invaded the Ctenomys lineage from an origin in caviids sometime before the ctenomyids began to diversify in early Pleistocene time. 相似文献
8.
Dunlop, J., Knighton, M. V. and White, D. W. R. 1988. Ion transportand the effects of acetic acid in white clover. I. Phosphateabsorption.J. exp. Bot. 39: 7988. The effect of acetic acid on phosphate absorption by white clovertissue has been examined. At 1·0 mol m3 acetic acid phosphateabsorption by roots of intact plants was stimulated by 36% (P< 0.001). At 5.0 and 10 mol m3 acetic acid there wasmarked inhibition of absorption by both suspension culturesof cells and the roots of intact plants. The inhibition waspH dependent with decreasing pH causing increased inhibition.Acetic acid caused changes in the membrane electropotential(E) with concentrations of 2·0 mol m3 or lesscausing persistent polarization whereas at 5·0 mol m3and higher concentrations the polarization was followed by agreater depolarization. Intracellular pH as measured by thefluorescence of fluorescein was lowered by acetic acid. Calculationsindicate that for white clover roots the proton motive force(pmf) appears to provide sufficient energy for phosphate absorption.It is proposed that acetic acid influences phosphate absorptionthrough its dependence on proton cotransport and that changesin J E affect the rate of phosphate absorption because of thedependence of the pmf on E. Key words: Phosphate absorption, intracellular pH, acetic acid, proton motive force, Trifolium repens, membrane electropotential 相似文献
9.
Dunlop, J., Knighton, M. V. and White, D. W. R. 1988. Ion transportand the effects of acetic acid in white clover. II. Potassiumabsorption.J. exp. Bot. 39: 8996. Acetic acid stimulated K+ influx into cells of white cloverin suspension culture and net K+ influx by roots of intact whiteclover plants. At concentrations of acetic acid up to 2·0mol m3 the stimulation continued unabated for at least2 h. However, at higher concentrations the rate of absorptiondeclined to near zero values after 2 h. When acetic acid wasremoved from the solution there was a net efflux of K+. Thestimulation was pH dependent with a maximum at pH 5·0.There was maximum stimulation at an acetic acid concentrationof 2·0 mol m3 Net H+ efflux was reduced by 1·0 mol m3 aceticacid. When Rb+ uptake and H+ efflux were measured at a rangeof RbCl concentrations Rb+ uptake increased with concentrationwhereas H+ efflux was maximum in the absence of Rb+ (and K+)and decreased as RbCl concentration was increased Acetic acid caused a hyperpolarization of the membrane electricalpotential difference (E) of about 25 mV. In 1·0 mol m3acetic acid the hyperpolarization persisted for at least 2 hwhereas at 10 mol m3 d E subsequently depolarized tovalues around 80 mV. With a slight lag, the time courseof the stimulation of the rate of K+ absorption followed thepolarization and depolarization of E. These results imply thatthe linkage between K+ and H+ movements is probably throughE. Key words: Proton efflux, membrane electrical potential difference, Trifolium repens 相似文献
10.
Mechanisms of action of abscisic acid at the cellular level 总被引:11,自引:2,他引:9