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141.
Structure and regulation of the anthranilate synthase genes in Pseudomonas aeruginosa: II. Cloning and expression in Escherichia coli 总被引:7,自引:0,他引:7
Crawford IP; Wilde A; Yelverton EM; Figurski D; Hedges RW 《Molecular biology and evolution》1986,3(5):449-458
The genes for the large and small subunits of anthranilate synthase (trpE
and trpG, respectively) have been cloned from Pseudomonas aeruginosa PAC174
into E. coli by R-prime formation with the broad-host- range plasmid
R68.44. Sequential subcloning into plasmid vectors reduced the active
Pseudomonas DNA fragment to a length of 3.1 kb. We obtained evidence that
this region contains the promoter for its own expression and retains a
vestigial regulatory response to tryptophan scarcity or excess.
相似文献
142.
143.
Concentrations of relaxin, prolactin, unchromatographed estradiol 17β (E2β) and progesterone (P4) were measured in serial samples of inferior vena caval blood, in three pigs, during late pregnancy, and parturition. Maximal relaxin concentrations occurred 60 to 24h before parturition, and ranged from 60 to 286ng/ml. Prolactin concentrations increased from 12.5ng/ml, 48 to 36 hours before parturition, to between 79 to 184ng/ml. At the time of the relaxin surge, E2β levels were high, and P4 concentrations were decreasing, thus raising the ratio. A surge in prolactin concentrations followed upon a decline of P4 to less than 10ng/ml, coinciding with the increase in relaxin concentrations in 2 gilts, and following the surge in relaxin in the third. Udder development occurred near the time of increased relaxin concentrations. ‘Milk let down’ followed maximal relaxin and prolactin concentrations in two gilts, and the increase in prolactin, rather than the increase in relaxin concentration, in the third. 相似文献
144.
Polypterids, the most basal actinopterygians, are a group of fish long-considered living fossils and holding a key position for understanding fish and tetrapod evolution. Knowledge of the natural history of Polypterus is limited, their having been studied in little detail since the early 1900s. The locomotory habits of wild Polypterus senegalus from Lake Albert, Uganda, were investigated in 2014. High-speed videography demonstrated the capability of large Polypterus to move overland successfully. Contrary to previous evidence, field observations found that terrestrial locomotion in Polypterus is not inherently restricted by body size. Evidence that Polypterus exhibit this behaviour as part of their natural life history can be found in the existence of environmental challenges and the presence of adaptations for amphibious life. 相似文献
145.
146.
Six ecologically central (old field) and marginal (strip mine) populations of the hexaploid Rumex acetosella were collected, grown under uniform conditions, and examined for genetic and morphological variation. Extensive electrophoretic variation was found in alcohol dehydrogenase and phosphoglucose isomerase, while other enzymes surveyed showed little or no variation. Hedrick's genotypic measure of identity revealed mean values of 0.506 for central populations, 0.836 for marginal populations, and 0.633 for comparisons of central with marginal populations. Alcohol dehydrogenase phenotypes had significantly fewer electromorphs per individual in marginal populations. Clones of individuals from both environments were subjected to different watering regimes. No significant differences in root/shoot ratio, leaf number, total leaf area, or relative growth rate were found between strip mine and old-field individuals within each watering treatment, although significant differences were found between watering treatments. There are small, but significant amounts of isozyme differentiation between central and marginal populations, while there was no such differentation for morphological characters. 相似文献
147.
Campetella Giandiego Chelli Stefano Wellstein Camilla Farris Emmanuele Calvia Giacomo Simonetti Enrico Borsukiewicz Lubov Vanderplank Sula Marignani Michela 《Plant Ecology》2019,220(7-8):765-776
Plant Ecology - We assessed the changes in community-weighted mean (CWM) and variability of specific leaf area (SLA) and leaf area (LA) of different Mediterranean shrub communities along an... 相似文献
148.
Abhilash Ponnath Hamilton E. Farris 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2010,196(9):613-628
Sensitivity to acoustic amplitude modulation in crickets differs between species and depends on carrier frequency (e.g., calling
song vs. bat-ultrasound bands). Using computational tools, we explore how Ca2+-dependent mechanisms underlying selective attention can contribute to such differences in amplitude modulation sensitivity.
For omega neuron 1 (ON1), selective attention is mediated by Ca2+-dependent feedback: [Ca2+]internal increases with excitation, activating a Ca2+-dependent after-hyperpolarizing current. We propose that Ca2+ removal rate and the size of the after-hyperpolarizing current can determine ON1’s temporal modulation transfer function
(TMTF). This is tested using a conductance-based simulation calibrated to responses in vivo. The model shows that parameter
values that simulate responses to single pulses are sufficient in simulating responses to modulated stimuli: no special modulation-sensitive
mechanisms are necessary, as high and low-pass portions of the TMTF are due to Ca2+-dependent spike frequency adaptation and post-synaptic potential depression, respectively. Furthermore, variance in the two
biophysical parameters is sufficient to produce TMTFs of varying bandwidth, shifting amplitude modulation sensitivity like
that in different species and in response to different carrier frequencies. Thus, the hypothesis that the size of after-hyperpolarizing
current and the rate of Ca2+ removal can affect amplitude modulation sensitivity is computationally validated. 相似文献
149.
150.
Emmanuele Farris FLS Alfonso Susanna Rossella Filigheddu Núria Garcia‐Jacas 《Botanical journal of the Linnean Society. Linnean Society of London》2014,175(3):453-467
Molecular approaches have greatly increased the number of confirmed homoploid hybrids, which suggests that the frequency of this phenomenon was underestimated in the past because it was much more difficult to detect than allopolyploidy. Centaurea is a suitable model group for studying homoploid speciation, as hybridization events have been commonly reported for this genus. Based on this, here we study Centaurea × forsythiana, a naturally occurring homoploid hybrid between two Sardinian endemics, C. horrida and C. filiformis, using a molecular approach involving nuclear and plastid markers, to understand the underlying population dynamics between homoploid hybrids and their parents. Our results confirm that C. × forsythiana is a hybrid between the above‐mentioned species and define the roles of the parents. Plastid markers point towards C. horrida as the maternal progenitor, and nuclear markers reveal that the other parental species, C. filiformis, is itself an old, stabilized homoploid hybrid related to the C. paniculata complex from the Italian mainland. Homoploid hybrid speciation is discussed and C. × forsythiana and C. filiformis are compared with other similar examples. The study confirms the importance of introgression between parental species mediated by hybrids and its potential implications in conservation. Furthermore, it shows how hybridization studies become even more complex when the parents are themselves of probable hybrid origin. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 175 , 453–467. 相似文献