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The phylogeny and systematics of European predacious Syrphidae (Diptera) based on larval and puparial stages 总被引:1,自引:0,他引:1
The external larval morphology of predacious Syrphidae is examined and compared with that of other groups of syrphids. Predacious larvae form a distinctive, monophyletic group. Relationships among 29 of the 34 European genera and subgenera are analysed using cladistic methods based on larval and puparial characters. Interpretation of the cladogram suggests that, within Syrphinae, a system of five tribes can be recognized and that a major trend has been a shift from ground layer to arboreal larval habitats, with an increasing degree of obligate dependence on soft-bodied Homoptera as prey. Generic diagnoses with biological and taxonomic notes are given and a key to genera based on larvae and puparia is provided. 相似文献
115.
A PREVIOUS communication from this laboratory demonstrated that the DNA polymerase of the Rauscher leukaemia virus is strongly inhibited in vitro by unprimed, single stranded polyribonucleotides1 as a result of competition between the polymers and the active template for the same enzyme binding site. This inhibition was apparently specific, since partially purified preparations of DNA polymerase from Escherichia coli and BALB/c mouse embryos were not inhibited in the same conditions. We attempted to determine therefore whether single stranded polyribonucleotides would have any effect on the activities of oncogenic RNA viruses in cultured cells. 相似文献
116.
GAO XIAOPING; FRANCIS DENNIS; ORMROD JOHN C.; BENNETT MICHAEL D. 《Annals of botany》1992,70(6):561-568
Double fertilization has been examined by electron microscopyin allohexaploid wheat, Triticum aestivum L. cv. Mardler. Serialsections through fertilized ovules revealed that following dischargeof the pollen tube contents into the degenerate synergid thelatter extended to form a continuum between the egg and centralcells. The two naked sperm nuclei were seen at the far end ofthis extended synergid. These observations suggest that thedegenerate synergid may play a role in transporting the spermnuclei to the site where they can be accepted by the egg andcentral cell. In comparison with double fertilization in Plumbagozeylanica L., we also suggest that the degenerate synergid preventsmale cytoplasms from being transmitted to the egg and centralcell. The present study also confirms that in the fertilizedcentral cell the maternal and paternal genomes remain physicallyseparate at least until the first nuclear division of the coenocyticphase of endosperm development. Double fertilization, degenerate synergid, Triticum aestivum 相似文献
117.
SYNOPSIS. Hearts of embryonic axolotls (Ambystoma mexicanum)homozygous for gene c do not beat in situ. Under appropriateculture conditions they rapidly commence beating, albeit lessvigorously than similarly explanted hearts of comparably stagednormal siblings. As part of this symposium, we have shown acine record demonstrating heartbeat in mutant hearts and comparingit to normal heartbeat. Myocardia of normal embryos exhibita characteristic pattern of birefringent, striated myofibrils.Mutants of the same stage contain hearts with birefringent fibrilsorganized in a pattern similar to that found in normal myocardia.A striking difference is that obvious striations are lackingin fibrils of the mutant. Electrophoresis of normal and mutanthearts in SDS-polyacrylamide gels shows that the major myofibrillarproteins are present. We conclude that induction of c/c heartshas been relatively normal and suggest that, due to the rapidityof recovery, the observed phenomena are perhaps due to somethingas simple as a defect in ionic conditions. 相似文献
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JOSEPH J. NAPOLITANO BARBARA HELENE SMITH FRANCIS J. PERSICO 《The Journal of eukaryotic microbiology》1967,14(1):108-109
SYNOPSIS. The size of the population of Naegleria gruberi at the time the amoebae are offered the opportunity to become flagellated is not a critical factor in the morphogenesis of this organism. Small populations (1-15 cells) readily become flagellated. Small populations (1-5 cells) washed several times also become flagellated. Clonal populations (25) have been established. All clones yield flagellates under the usual conditions. It is suggested that the physiological state of the amoebae is a factor in determining the number of cells that will undergo morphogenesis at any given time. 相似文献
119.
Contrasting effects of climate and CO2 on Amazonian ecosystems since the last glacial maximum 总被引:1,自引:0,他引:1
The nature of Amazonian ecosystem responses to the large-scale environmental changes characterizing glacial–interglacial cycles is poorly understood. We investigated this issue with a series of transient, continuous 21 000-year simulations using a dynamic process-based ecosystem model. Our results indicate that the Amazon Basin has been dominated by evergreen rain forests since the last glacial maximum (LGM), demonstrating the resilience of this ecosystem to glacial–interglacial environmental change. We find that biome shifts in ecotonal areas since the LGM were driven predominantly by climate change, while coincident, increased ecosystem carbon storage throughout the Amazon Basin was driven largely by CO2 . Our findings imply that recent observed biomass increases in contemporary rain forest plots might be part of a long-term trend driven by the anthropogenic rise in CO2 over recent centuries. 相似文献
120.
CAREY FRANCIS G.; TEAL JOHN M.; KANWISHER JOHN W.; LAWSON KENNETH D.; BECKETT JAMES S. 《Integrative and comparative biology》1971,11(1):137-143
SYNOPSIS. Two groups of fishes, the tuna and the lamnid sharks,have evolved ounter-currentheat-exchange mechanisms for conservingmetabolic heat and raising their body temperatures. Warm musclecan produce more power, and considering the other adaptationsfor fast swimming in these fish, it seems likely that the selectiveadvantages of greater speed made possible by the warm musclewere important in the evolution of this system. Some tunas suchas the yellowfin and skip jack are at a fixed temperature differenceabove the water, but bluefin tuna can thermoregulate. Telemetryexperiments show that the bluefin tuna can maintain a constantdeep body temperature during marked changes in the temperatureof its environment. 相似文献