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1.
W. Melville Arnott 《BMJ (Clinical research ed.)》1953,1(4821):1219-1220
2.
Stanley Melville 《BMJ (Clinical research ed.)》1932,2(3736):283-284
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4.
Structural aspects of Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] tuberculate ectomycorrhizae
H. B. Massicotte L. H. Melville C. Y. Li R. L. Peterson 《Trees - Structure and Function》1992,6(3):137-146
Summary Tubercles of Pseudotsuga menziesii consisted of clusters of ectomycorrhizae surrounded by a peridiumlike rind. Energy dispersive spectroscopy demonstrated that crystals found in the zone of loose hyphae extending from the inner rind to the mantle of each root probably contain calcium oxalate. Inner mantle and Hartig net hyphae showed a labyrinthine branching pattern and stored carbohydrates and protein. The Hartig net formed up to inner cortical cells which had thickened, darkly stained walls. Bacteria were located either along with hyphae within the rind or as colonies on the surface of the tubercle. 相似文献
5.
Regulation of carbon flow in Selenomonas ruminantium grown in glucose-limited continuous culture. 总被引:5,自引:3,他引:2
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We have applied a model that permits the estimation of the sensitivity of flux through branch point enzymes (D. C. LaPorte, K. Walsh, and D. E. Koshland, J. Biol. Chem. 259:14068-14075, 1984) in order to analyze the control of flux through the lactate-acetate branch point of Selenomonas ruminantium grown in glucose-limited continuous culture. At this branch point, pyruvate is the substrate of both the NAD-dependent L-(+)-lactate dehydrogenase (LDH) and the pyruvate:ferredoxin oxidoreductase (PFOR). The LDH was purified, and it exhibited positive cooperativity for the binding of pyruvate. The LDH had an [S].5 for pyruvate of 0.43 mM, a Hill coefficient of 2.4, and a K' equal to 0.13 mM. The PFOR, assayed in cell extracts, exhibited Michaelis-Menten kinetics for pyruvate, with a Km of 0.49 mM. Carbon flux through the LDH and the PFOR increased 80-fold and 3-fold, respectively, as the dilution rate was increased from 0.07 to 0.52 h-1 in glucose-limited continuous culture. There was nearly a twofold increase, from 6.5 to 11.2 mumol min-1 mg of protein-1 in the specific activity (i.e., maximum velocity) of the LDH at dilution rates of 0.11 and 0.52 h-1, respectively. A flux equation was used to calculate the intracellular concentration of pyruvate; a fourfold increase in pyruvate, from 0.023 to 0.093 mM, was thereby predicted as the dilution rate was increased from 0.07 to 0.52 h-1. When these calculated values of intracellular pyruvate concentration were inserted into the flux equation, the predicted values of flux through the LDH and the PFOR were found to match closely the flux actually measured in the chemostat-grown cells. Thus, the 80-fold increase in flux through the LDH was due to a twofold increase in the maximum velocity of the LDH and a fourfold increase in the intracellular pyruvate concentration. In addition, the flux through the LDH exhibited ultrasensitivity to changes in both the maximum velocity of the LDH and the intracellular concentration of pyruvate. The flux through the PFOR exhibited ultrasensitivity to changes in the maximum velocity of the LDH and hyperbolic sensitivity to changes in the intracellular concentration of pyruvate. 相似文献
6.
By encapsulating a pH-sensitive dye, phenol red, in multilamellar liposomes of DMPC, DPPC and DMPC/DPPC mixtures, the permeability of these phospholipid bilayers to dye as a function of temperature has been studied. For both DMPC and DPPC liposomes, dye release begins well below the main gel-to-liquid-crystalline phase transition (24°C and 42°C, respectively) at temperatures corresponding to the onset of the pretransition (about 14°C and 36°C, respectively) with DPPC liposomes exhibiting a permeability anomaly at the main phase transition (42°C). The perturbation occurring in the bilayer structure that allows the release of encapsulated phenol red (approx. 5 Å diameter) is not sufficient to permit the release of encapsulated haemoglobin (approx. 20 Å diameter, negatively charged). In liposomes composed of a range of DMPC/DPPC mixtures, dye release commences at the onset of the pretransition range (determined by optical absorbance measurements) and increases with increasing temperature until the first appearance of liquid crystalline phase after which no further dye release occurs. Interestingly, the dye retaining properties of DMPC and DPPC liposomes well below their respective pretransition temperature regions are very different: DMPC liposomes release much encapsulated dye at incubation temperatures of 5°C whilst DPPC liposomes do not. 相似文献
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9.
Anonymous nuclear DNA markers in the American oyster and their implications for the heterozygote deficiency phenomenon in marine bivalves 总被引:4,自引:0,他引:4
A puzzling population-genetic phenomenon widely reported in allozyme
surveys of marine bivalves is the occurrence of heterozygote deficits
relative to Hardy-Weinberg expectations. Possible explanations for this
pattern are categorized with respect to whether the effects should be
confined to protein-level assays or are genomically pervasive and expected
to be registered in both protein- and DNA-level assays. Anonymous nuclear
DNA markers from the American oyster were employed to reexamine the
phenomenon. In assays based on the polymerase chain reaction (PCR), two
DNA-level processes were encountered that can lead to artifactual genotypic
scorings: (a) differential amplification of alleles at a target locus and
(b) amplification from multiple paralogous loci. We describe symptoms of
these complications and prescribe methods that should generally help to
ameliorate them. When artifactual scorings at two anonymous DNA loci in the
American oyster were corrected, Hardy-Weinberg deviations registered in
preliminary population assays decreased to nonsignificant values.
Implications of these findings for the heterozygote-deficit phenomenon in
marine bivalves, and for the general development and use of PCR-based
assays, are discussed.
相似文献
10.
Much of eastern Australia's coastal lowlands are underlain by Holocene sulfidic sediments. Large areas have been drained for agriculture. Drained, sulfidic sediments oxidize and produce highly acidic discharge (pH<4) with significant impacts on estuarine ecosystems. The rate of production of acid from drained floodplains is between 100 to 300 kg H2SO4 /ha/y and hundreds of tonnes of H2SO4 can be discharged in a single flood from the floodplain. Generation and export of acidity is controlled by the water balance of the floodplain, the characteristics of the drainage system and the distribution of sulfides. Evapotranspiration by native plants and crops plays a dominant role in the oxidation of sediments in dry periods. In wet periods, upland discharges to floodplains dominate the water balance. Drain spacing and drain depth are critical factors in the export of acidity into coastal streams. Amelioration of acidic outflows requires an understanding of the interaction between chemical and hydrological processes in sulfidic landscapes. Redesign of drainage systems to manage surface waters and reduce drain density with the treatment of drains with lime offer promise for treating acidic discharge and reducing impacts. Reflooding of drained, partially oxidized floodplains with freshwater may not be a panacea because of the large volumes of acid stored in the soil, a lack of labile organic matter in the sediments needed to reduce sulfate and irreversible changes to the soil due to oxidation. Tidal brackish water reflooding of unproductive acidified lowlands offers promise for rehabilitating wetlands. Sulfidic wetlands which are still undrained should remain so unless all acidic discharge can be treated. 相似文献