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81.
An unusual genotype of Toxoplasma gondii is common in California sea otters (Enhydra lutris nereis) and is a cause of mortality 总被引:2,自引:0,他引:2
Miller MA Grigg ME Kreuder C James ER Melli AC Crosbie PR Jessup DA Boothroyd JC Brownstein D Conrad PA 《International journal for parasitology》2004,34(3):275-284
Toxoplasma gondii-associated meningoencephalitis is a significant disease of California sea otters (Enhydra lutris nereis), responsible for 16% of total mortality in fresh, beachcast carcasses. Toxoplasma gondii isolates were obtained from 35 California otters necropsied between 1998 and 2002. Based on multi-locus PCR-restriction fragment length polymorphism and DNA sequencing at conserved genes (18S rDNA, ITS-1) and polymorphic genes (B1, SAG1, SAG3 and GRA6), two distinct genotypes were identified: type II and a novel genotype, here called type x, that possessed distinct alleles at three of the four polymorphic loci sequenced. The majority (60%) of sea otter T. gondii infections were of genotype x, with the remaining 40% being of genotype II. No type I or III genotypes were identified. Epidemiological methods were used to examine the relationship between isolated T. gondii genotype(s) and spatial and demographic risk factors, such as otter stranding location and sex, as well as specific outcomes related to pathogenicity, such as severity of brain inflammation on histopathology and T. gondii-associated mortality. Differences were identified with respect to T. gondii genotype and sea otter sex and stranding location along the California coast. Localised spatial clustering was detected for both type II (centred within Monterey Bay) and x (centred near Morro Bay)-infected otters. The Morro Bay cluster of type x-infected otters overlaps previously reported high-risk areas for sea otter infection and mortality due to T. gondii. Nine of the 12 otters that had T. gondii-associated meningoencephalitis as a primary cause of death were infected with type x parasites. 相似文献
82.
This study compares the thermal ecology of male bearded dragon lizards (Pogona barbata) from south-east Queensland across two seasons: summer (1994–1995) and autumn (1995). Seasonal patterns of body temperature
(T
b) were explored in terms of changes in the physical properties of the thermal environment and thermoregulatory effort. To
quantify thermoregulatory effort, we compared behavioral and physiological variables recorded for observed lizards with those
estimated for a thermoconforming lizard. The study lizards' field T
bs varied seasonally (summer: grand daily mean (GDM) 34.6 ± 0.6°C, autumn: GDM 27.5 ± 0.3°C) as did maximum and minimum available
operative temperatures (summer: GDM T
max 42.1 ± 1.7°C, T
min 32.2 ± 1.0°C, autumn: GDM T
max 31.7 ± 1.2°C, T
min 26.4 ± 0.5°C). Interestingly, the range of temperatures that lizards selected in a gradient (selected range) did not change
seasonally. However, P. barbata thermoregulated more extensively and more accurately in summer than in autumn; lizards generally displayed behaviors affecting
heat load nonrandomly in summer and randomly in autumn, leading to the GDM of the mean deviations of lizards' field T
bs from their selected ranges being only 2.1 ± 0.5°C in summer, compared to 4.4 ± 0.5°C in autumn. This seasonal difference
was not a consequence of different heat availability in the two seasons, because the seasonally available ranges of operative
temperatures rarely precluded lizards from attaining field T
bs within their selected range, should that have been the goal. Rather, thermal microhabitat distribution and social behavior
appear to have had an important influence on seasonal levels of thermoregulatory effort.
Received: 28 April 1997 / Accepted: 29 December 1997 相似文献
83.
The demonstration that interleukin 2 (IL-2) is a lectin specific for
oligomannosides allows to understand a new function for this cytokine: as a
bifunctional molecule when bound to its receptor ss, IL-2 associates the
latter which the CD3/TCR complex, interacting with oligosaccharides of CD3
through its carbohydrate-recognition domain (Zanetta et al. , 1996,
Biochem. J., 318, 49-53). This induces the tyrosine phosphorylation of the
IL-2R beta by ++p56(lck) , the first step of the IL-2-dependent signaling.
Since this specific association is disrupted in vitro by oligomannosides
with five and six mannose residues, we made the hypothesis that pathogenic
cells or microorganisms could bind IL-2, consequently disturbing the IL-2-
dependent response. This study shows that the pathogenic yeast Candida
albicans (in contrast with nonpathogenic yeasts) binds high amounts of IL-2
as did cancer cells. In contrast with cancer cells, yeasts do not bind the
Man6GlcNAc2-specific lectin CSL, an endogenous "amplifier of activation
signals" (Zanetta et al. , 1995, Biochem. J., 311, 629-636).
相似文献
84.
G. C. Grigg F. Seebacher L. A. Beard D. Morris 《Proceedings. Biological sciences / The Royal Society》1998,265(1407):1793-1799
We monitored behaviour and environmental and body temperatures (Tb) in summer and winter in 11 salt-water crocodiles (Crocodylus porosus), of body mass 32 to 1010kg, free-ranging in naturalistic captivity in northern Australia. We found pronounced daily cycles in air and water temperatures in both winter (16 to 33 degrees C and 20 to 31degrees C, respectively) and summer (21 to 45 degrees C and 24 to 36 degrees C, respectively). In winter, crocodiles exposed themselves to the sun during the day and stayed in the water at night. In summer, they remained in the water during the day and emerged onto land at night. Body temperature showed a daily cycle the amplitude of which decreased with increasing mass, from 3.5 degrees C (mass 32kg) to 1.0 degrees C (660kg) in summer, and from 3.5 degrees C (42kg) to 1.4 degrees C (1010kg) in winter. Underlying the daily cycles in Tb were intermediate (10 to 13 day, tidal?) and seasonal cycles. Overall, values of modal Tb ranged from 25.1 to 28.7 degrees C in winter and from 28.4 to 33.6 degrees C in summer, trending upwards with body size. This pattern of continuous oscillations in Tb, with no daily plateau, is conspicuously different from that seen in crocodilians of small sizes and from the pattern usually regarded as typical of reptiles in general. 相似文献
85.
86.
Effect of insulin on ultrastructure and glycogenesis in primary cultures of adult rat hepatocytes
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Insulin in the presence of high concentrations of glucose has a beneficial trophic effect on the development of primary cultures of hepatocytes. Compared to the situation observed in hormone-free control cultures, the flattening of the reaggregated hepatocytes is enhanced, and the reconstituted cell trabeculae are enlarged and tend to form a confluent monolayer after 3 days; the survival time is prolonged from 3 to 5 or 6 days. Ultrastructural modifications are also initiated by insulin; numerous glycogen particles appear after 24 h, in between the cisternae of the proliferated smooth endoplasmic reticulum. After 48 h, large amounts of glycogen are stored, and numerous polysomes are present. A small number of cells showed an increased synthesis of lipid droplets in the lumen of the smooth endoplasmic reticulum and form liposomes at the same time. After 72 h, cytolysomes filled with glycogen develop, simulating glycogenosis type II. Simultaneously, microtubules and microfilaments, closely related to numerous polysomes, appear in cytoplasmic extensions constituting undulating membranes. The biochemical data demonstrate that, in the absence of insulin, a high concentration of glucose stimulates glycogenesis and hinders glycogenolysis. This effect of glucose on polysaccharide synthesis is progressively lost. The addition of insulin to the culture induces after 48 and 72 h, a three- to fivefold increase of the glucose incorporation into glycogen, as compared to the controls. The presence of insulin is required to maintain the hepatocyte's capacity to store glycogen. Glycogen synthetase is converted into its active form under the influence of glucose. Insulin increases the rate of activation. 相似文献
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90.
In spite of the increasing application of DNA fingerprinting to natural
populations and to the genetic identification of humans, explicit methods
for estimation of basic population genetic parameters from DNA
fingerprinting data have not been developed. Contributing to this omission
is the inability to determine, for multilocus fingerprinting probes,
relatively important genetic information, such as the number of loci, the
number of alleles, and the distribution of these alleles into specific
loci. One of the most useful genetic parameters that could be derived from
such data would be the average heterozygosity, which has traditionally been
employed to measure the level of genetic variation within populations and
to compare genetic variation among different loci. We derive here explicit
formulas for both the estimation of average heterozygosity at multiple
hypervariable loci and a maximum value for this estimate. These estimates
are based upon the DNA restriction-pattern matrices that are typical for
fingerprinting studies of humans and natural populations. For several
empirical data sets from our laboratory, estimates of average and maximal
heterozygosity are shown to be relatively close to each other. Furthermore,
variances of these statistics based on simulation studies are relatively
small. These observations, as well as consideration of the effect of
missing alleles and alternate numbers of loci, suggest that the average
heterozygosity can be accurately estimated using phenotypic DNA fingerprint
patterns, because this parameter is relatively insensitive to the lack of
certain genetic information.
相似文献