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441.
SYNOPSIS. Sera from 270 domestic and wild mammals were tested for antibodies against Toxoplasma gondii by the indirect hemagglutination method. The specificity of reactions was determined by the hemagglutination-inhibition test. Positive results at a titer of 1:64 were given by 10 of 138 cattle, 3 of 74 swine, 1 of 8 cats and none of 3 horses. Of the wild animals tested, only 1 of 9 woodchucks was positive; 17 raccoons, 14 opossums and 7 skunks were negative.  相似文献   
442.
Mark recapture and morph frequency data, gathered during a population irruption of Hypolimnas misippus in southern Ghana, provide evidence for apostatic and mimetic selection. During a period of low adult survival, both the recapture rate and the frequency of the commonest morph ( misippus ) were significantly reduced. Selection against this form increased phenotypic diversity and generated significant disequilibrium in the combinations of unlinked fore- and hindwing phenotypes. There was also evidence for selection against those forms (weak alcippoides ) which most closely resemble misippus . Other morphs, including both good mimics of Danaus chrysippus and rare non-mimics, showed no reductions in recapture rate during the period of low survival, but only the good mimics increased significantly in frequency. The results provide a predictive ecological model for density-dependent selection by predators which is consistent with field data from previous studies of H. misippus in Ghana and Tanzania. Their evolutionary implications are discussed, and it is suggested that anomalies in the mimicry of this species may be partly due to lack of predation when it is scarce.  相似文献   
443.
Two diastems in the King Ferry Shale Member (Ludlowville Formation) are the result of local submarine erosion. These discontinuities, traceable from the Cayuga Valley to Seneca Lake, are marked by bioencrusted hiatus-concretions, and both diastems display westward erosional overstep of underlying beds. Hiatus-concretions show complex sequential histories of in situ formation, exhumation, and biodegradation. Activity of bottom organisms influenced erosion; substrate modification by infauna acted to trigger or accelerate sediment loss in a low energy setting. Both diasterns are developed along a depth related paleoenvironmental gradient; submarine erosion in this area is controlled, in part, by the presence of a gentle northwest dipping paleoslope. Juxtaposition of three conditions: bioturbation of surface muds, episodic wave or current impingement on these muds, and substrate inclination resulted in local sea floor erosion through a process of downslope sediment transport and dispersion. King Ferry diastems are termed stratomictic . Stratomictic discontinuities are erosional breaks which lack discrete hiatal surfaces due to vertical sediment mixing by infauna. They include several other examples from the New York Devonian and probably have analogs in numerous sedimentary sequences world-wide.  相似文献   
444.
Atmospheric CO2 (Ca) concentration has increased significantly during the last 20 000 years, and is projected to double this century. Despite the importance of belowground processes in the global carbon cycle, community‐level and single species root responses to rising Ca are not well understood. We measured net community root biomass over 3 years using ingrowth cores in a natural C3–C4 grassland exposed to a gradient of Ca from preglacial to future levels (230–550 μmol mol?1). Root windows and minirhizotron tubes were installed below naturally occurring stands of the C4 perennial grass Bothriochloa ischaemum and its roots were measured for respiration, carbohydrate concentration, specific root length (SRL), production, and lifespan over 2 years. Community root biomass increased significantly (P<0.05) with Ca over initial conditions, with linear or curvilinear responses depending on sample date. In contrast, B. ischaemum produced significantly more roots at subambient than elevated Ca in minirhizotrons. The lifespan of roots with five or more neighboring roots in minirhizotron windows decreased significantly at high Ca, suggesting that after dense root growth depletes soil resource patches, plants with carbon surpluses readily shed these roots. Root respiration in B. ischaemum showed a curvilinear response to Ca under moist conditions in June 2000, with the lowest rates at Ca<300 μmol mol?1 and peak activity at 450 μmol mol?1 in a quadratic model. B. ischaemum roots at subambient Ca had higher SRLs and slightly higher carbohydrate concentrations than those at higher Ca, which may be related to drier soils at low Ca. Our data emphasize that belowground responses of plant communities to Ca can be quite different from those of the individual species, and suggest that complex interactions between and among roots and their immediate soil environment influence the responses of root physiology and lifespan to changing Ca.  相似文献   
445.
By the use of isoelectric focusing in polyacrylamide gels serum samples from 146 Alaskan wolves were studied with regard to transferrin (Tf) and esterase (ArE) polymorphism, comparing the phenotypic band patterns with those of selected Norwegian dogs. The study revealed Tf and ArE polymorphisms in the wolf with phenotypic band patterns being indistinguishable from the corresponding ones in dogs. This suggests the occurrence of the same two common Tf alleles in the wolf as in the dog. In the ArE system the results are consistent with the occurrence of three alleles which also occur in dogs whereas a fourth allele, so far not seen in dogs, is seen in Alaskan wolves.  相似文献   
446.
In the summer of 1979–80, there was a sharp decline in the koala population along Mungalalla Creek in south-western Queensland. The decline was associated with a heatwave and drought. Live animals and carcasses were counted soon after the decline and at three subsequent periods. It was estimated that more than 63% of the population died. The drought and heatwave caused extensive leaf-fall and/or browning of the foliage in food trees along stretches of dry creek. The proximate cause of death was thought to be a combination of malnutrition and dehydration. There was evidence, including the differential survival of koalas along the creek, of marked heterogeneity in the quality of the habitat. At sites where the trees were not affected (mainly on large permanent water-holes) koalas had good body condition and mortality was low, whereas on stretches of dry creek (marginal habitat), koalas were in poor health (poor condition, anaemia, high tick loads) and mortality was very high. Survival of the population was not threatened because many animals survived at the permanent water-holes. There is evidence that mortality was highest among young animals which may be excluded from optimal sites by older dominant animals. In the years after the crash, continuing drought appeared to prevent recovery of the population. It is thought that such population crashes are rare events as they are apparently caused partly by unusual climatic conditions.  相似文献   
447.
448.
449.
Adaptational Significance of the Patterns of Ophiuroid Development   总被引:1,自引:0,他引:1  
There is only limited information on ophiuroid developmentalpatterns, larvae being known for only 4% of the 2000 livingophiuroids. Three modes of development are distinguished (planktotrophic,direct, abbreviated) on the basis of egg size and number, larvalform and life span, and post-larval size. This generalizationis applied to an analysis of the larval form(s) of deep-seaophiuroids and the ancestral ophiuroid larva. Quantitative informationon rate of development and reproductive period, which has beenlacking for viviparous ophiuroids, is presented for Axiognathus( = Amphipholis) squamatus on the basis of original size-frequencydata. Reproduction is seasonal in the population studied anddevelopment to metamorphosis takes no longer than for planktotrophicspecies though the brooding period ranges from 3 to 7 months.Additional data indicate post-larvae of planktotrophic specieshave fewer arm segments than newly-hatched viviparous young,supporting the hypothesis that large size of juveniles is characteristicand selectively advantageous for viviparous ophiuroids.  相似文献   
450.
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