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61.
Baldauf SA Thünken T Frommen JG Bakker TC Heupel O Kullmann H 《International journal for parasitology》2007,37(1):61-65
Many parasites with complex life cycles increase the chances of reaching a final host by adapting strategies to manipulate their intermediate host's appearance, condition or behaviour. The acanthocephalan parasite Pomphorhynchus laevis uses freshwater amphipods as intermediate hosts before reaching sexual maturity in predatory fish. We performed a series of choice experiments with infected and uninfected Gammarus pulex in order to distinguish between the effects of visual and olfactory predator cues on parasite-induced changes in host behaviour. When both visual and olfactory cues, as well as only olfactory cues were offered, infected and uninfected G. pulex showed significantly different preferences for the predator or the non-predator side. Uninfected individuals significantly avoided predator odours while infected individuals significantly preferred the side with predator odours. When only visual contact with a predator was allowed, infected and uninfected gammarids behaved similarly and had no significant preference. Thus, we believe we show for the first time that P. laevis increases its chance to reach a final host by olfactory-triggered manipulation of the anti-predator behaviour of its intermediate host. 相似文献
62.
The banana weevil, Cosmopolites sordidus (Germar), is an important pest of bananas. Predatory ants are increasingly being viewed as possible biological control agents of this pest because they are capable of entering banana plants and soil in search of prey. We studied ant predation on banana weevil in Uganda in crop residues and live plants in both laboratory and field experiments. Field studies with live plants used chemical ant exclusion in some plots and ant enhancement via colony transfer in others to measure effects of Pheidole sp. 2 and Odontomachus troglodytes Santschi on plant damage and densities of immature banana weevils.In crop residues, an important pest breeding site, twice as many larvae were removed from ant-enhanced plots as in control plots. In young (2 month) potted suckers held in shade houses, ant ability to reduce densities of banana weevil life stages varied with the weevil inoculation rate. At the lowest density (2 female weevils per pot), densities of eggs, larvae, and pupae were reduced by ants. At higher rates there was no effect. In older suckers (5–11 months) grown in larger containers, banana weevil densities were not affected by ants, but damage levels were reduced. In a field trial lasting a full crop cycle (30 months), we found that the ants tested reduced the density of banana weevil eggs in suckers during the crop, but did not affect larval densities in the sampled suckers. However, most larvae occur in the main banana plants, rather than associated suckers. Nevertheless, levels of damage in mature plants at harvest did not differ between Amdro-treated and ant-enhanced plots, suggesting the ant species studied were not able to provide economic control of banana weevil under our test conditions. 相似文献
63.
Erling S. Nordøy Lars P. Folkow Vladimir Potelov Vitaly Prischemikhin Arnoldus Schytte Blix 《Polar Biology》2008,31(9):1119-1135
Eight adult female harp seals (Pagophilus
groenlandicus) of the White Sea–Barents Sea stock were tagged with satellite-linked dive recorders during the nursing period and followed
from breeding in late February 1995 until moulting in late April 1995. Another ten adult harp seals of both sexes were tagged
and followed from moult in early May 1996 until breeding in late February the following year. Between breeding and moult the
seals were distributed along the coasts of Kola of Russia and eastern Finnmark of Norway, coinciding in time and space with
the spawning capelin (Mallotus villosus). Between moulting and breeding they encircled the entire Barents Sea, mostly in open water, using the water column from
20 to 300 m, and in so doing by and large reflecting the annual migrations of the capelin. Capelin is therefore assumed to
be the main source of prey for the White Sea–Barents Sea stock of harp seals, to be substituted, in part, by amphipods (e.g.
Themisto libellula) in mid-summer and polar cod (Boreogadus saida) and herring (Clupea pallasii) in late autumn and winter. These data provide a baseline for the evaluation of the effects of future climatic change in
the rich Barents Sea ecosystem. 相似文献
64.
Populations of metazoan microfauna (nematodes, rotifers and tardigrades) are patchily distributed on mountain outcrops penetrating
the ice sheet (nunataks) in continental Antarctica. The abundance and fauna composition of microscopic animals vary greatly
also among samples from similar types of habitats. Occurrence of similar seemingly habitable sites without microfauna and
sites with various combinations of animal taxa indicates that stochastic colonization processes as well as local environmental
factors and historical factors influence faunal composition in a specific habitable patch. The abundance of nematodes, rotifers
and tardigrades in various combinations of co-occurrence was analyzed. One objective was to investigate if biotic interactions
structuring these simple communities could be observed. The 368 samples analysed originate from three kinds of habitats, viz.
mosses, ornithogenic soils and fellfield soils, obtained from 14 nunataks in Dronning Maud Land, East Antarctica. It is suggested
that high population densities of any of the three animal groups, when they were found alone and lower densities, when they
coexisted with other taxa could indicate the presence of competition or predation. However, the great variability in microfauna
densities for similar habitable patches made it difficult to find significant differences among population densities in samples
with varying complexity. 相似文献
65.
2004年7月至2007年1月在内蒙古达赉湖国家级自然保护区,通过跟踪调查搜集到狼(Canis lupus)捕食家畜的数据,共计95起捕食事件,425(头只)家畜遭到捕食,折合人民币186 575.00元.这些数据包括:捕食事件发生的时间,被捕食家畜的数量、类型、年龄,狼痕迹照片和捕食点的GPS数据.运用Mann.Whitney U检验对数据的差异性进行了检验;对捕食点的空间属性进行了量化,用多个生态因子对其进行了描述;运用主成分分析(PCA)分析了多因子中的主要成分.结果表明,在达赉湖狼主要捕食顺序是:羊(绵羊和山羊)、牛、马,骆驼和驴很少捕食,对羊存在偏好,被捕食个体年龄没有偏好.捕食的数目存在偏差,存在明显的机会性,捕食事件多发生在9月至次年2月的冰冻期.影响捕食地的生态变量重要性排序为:人为干扰距离、生境类型、猎物种类、卧息地距离、隐蔽度、水源距离、捕食季节、捕食数量、围栏距离9个生态指标.对这些生态因子的分析表明:前三个特征值的累计贡献率已达到81.544%,可以较好地反映捕食地的生境特征,影响狼捕食家畜的前三位主要因子是隐蔽度、人为干扰距离和水源距离,而与猎物种类相关不大.评价影响狼对家畜捕食的主要因素:人口的剧增使得野生动物的栖息地减少,过度放牧使得草场退化,是导致狼捕食家畜的重要原因;野外有蹄类的匮乏是导致狼捕食家畜的主要原因.建议改变目前的放牧方式,加强对家畜的看护,重新引入当地的一些原生物种,补充狼的自然食物,以缓解狼对家畜的捕食. 相似文献
66.
Fredrik Dalerum Michael J. Somers Kyran E. Kunkel Elissa Z. Cameron 《Biodiversity and Conservation》2008,17(12):2939-2949
Biodiversity in southern Africa is globally extraordinary but threatened by human activities. Although there are considerable
biodiversity conservation initiatives within the region, no one has yet assessed the potential use of large carnivores in
such actions. Surrogate approaches have often been suggested as one such way of capitalizing on large carnivores. Here we
review the suitability of the large carnivore guild (i.e., brown hyaena Hyaena hyaena, spotted hyaena Crocuta crocutta, cheetah Acinonyx jubatus, leopard Panthera pardus, lion Panthea leo and African wild dog Lycaon pictus) to act as surrogate species for biodiversity conservation in southern Africa. We suggest that the guild must be complete
for the large carnivores to fully provide their role as ecological keystones. The potential for large carnivores to act as
umbrella and indicator species seems limited. However, self-sustaining populations of large carnivores may be useful indicators
of unfragmented landscapes. Moreover, diversity within the large carnivore guild may reflect overall biodiversity. Although
the global appeal of the large African carnivores makes them important international flagships, we stress that international
conservation funding must be linked to local communities for them to be important also locally. In summary, we suggest that
the flagship value of these large carnivores should be used to promote biodiversity conservation in the region, and that the
suggested relationship between large carnivore diversity and overall biodiversity is empirically tested. Finally we suggest
that direct conservation activities should focus on enhancing the keystone values of large carnivores through complete guild
conservation and restoration. 相似文献
67.
Christoph Randler 《Journal of Ethology》2008,26(3):309-316
Predation is one of the most selective forces in evolution and, thus, predation may select against hybrids in narrow hybrid
zones. It may be possible that parental phenotypes and hybrids differ in their responses towards predators or humans. As predation
is difficult to observe I used flight-initiation distance (FID) as a metric of risk assessment. FID is a measurable outcome
of the trade-off between fleeing and remaining. Here, I tested whether hybrid and parent crow phenotypes (Corvus corone, Corvus cornix) from the hybrid zone in Eastern Germany differ in their FID. Further, I measured many environmental and social variables
to control statistically for their influence on FID. I sampled 154 individuals (53 hooded crows, 54 carrion crows, and 48
hybrids) in the hybrid zone in eastern Germany. I calculated a general linear model using a stepwise backward procedure to
establish a minimum model containing only significant variables that explained FID in crows. The variable phenotype (hooded,
carrion, hybrid) was then added to the model. There were no differences in FID between hybrids and both parental phenotypes
types, suggesting similar risk assessment. This suggests that hybrids may behave similarly in their decision to flee as their
parent phenotypes, which, in turn, provides no evidence for a selective disadvantage. An additional analysis focusing on pure
phenotypic flocks showed that hybrids in pure hybrid flocks had a lower FID than both parental species in pure flocks. This
suggests that hybrids in pure hybrid flocks may be at a disadvantage. 相似文献
68.
Parasites can fundamentally alter the cost–benefit ratio of living in a group, e.g. if infected individuals increase the predation
risk of shoal mates. Here, the effect of an infection with a trematode, Uvulifer sp. (Diplostomatidae) on the shoaling behaviour of female western mosquitofish, Gambusia affinis, was investigated. The parasite examined causes a direct phenotypical change of the host by forming black spots on its body
surface. When given a choice between a stimulus shoal and no shoal, we found shoaling tendencies to be significantly reduced
in infected focal fish. In another experiment, we tested for association preferences relative to the infection status of the
stimulus fish. Given the choice between an infected and a healthy stimulus fish, both infected and healthy focal fish preferred
to associate with non-infected stimulus fish. Our results suggest that (1) the cost–benefit ratio of shoaling might be different
for infected and non-infected individuals. Infected fish may be more affected by competition for food within a shoal. (2)
Associating with infected conspecifics appears to be costly for female mosquitofish, maybe due to increased predation risk. 相似文献
69.
Brett R. Dumbauld David L. Holden Olaf P. Langness 《Environmental Biology of Fishes》2008,83(3):283-296
Green sturgeon, Acipenser medirostris, and white sturgeon, Acipenser transmontanus, are frequent inhabitants of coastal estuaries from northern California, USA to British Columbia, Canada. An analysis of
stomach contents from 95 green sturgeon and six white sturgeon commercially landed in Willapa Bay, Grays Harbor, and the Columbia
River estuary during 2000–2005 revealed that 17–97% had empty stomachs, but those fish with items in their guts fed predominantly
on benthic prey items and fish. Burrowing thalassinid shrimp (mostly Neotrypaea californiensis) were important food items for both white and especially for green sturgeon taken in Willapa Bay, Washington during summer
2003, where they represented 51% of the biomass ingested (84.9% IRI). Small pits observed in intertidal areas dominated by
these shrimp, are likely made by these sturgeon and we present evidence from exclusion studies and field observation that
the predator making the pits can have a significant cumulative negative effect on burrowing shrimp density. These burrowing
shrimp present a threat to the aquaculture industry in Washington State due to their ability to de-stabilize the substrate
on which shellfish are grown. Despite an active burrowing shrimp control program in these estuaries, it seems unlikely that
current burrowing shrimp abundance and availability as food is a limiting factor for threatened green sturgeon stocks. However,
these large predators may have performed an important top down control function on shrimp populations in the past when they
were more abundant. 相似文献
70.
Two medium-sized herbivores with high trophic overlap coexist on rocky outcrops in the Patagonian landscape: the southern
vizcacha (Lagidium viscacia), which is a native rock specialist, and the European hare (Lepus europaeus), which is a non-native species. We determined the patterns of space use related to distance from outcrops and analyzed spatial
overlap between the two species. There were significant differences between the two species in the use of space adjacent to
outcrops. The southern vizcacha mainly uses short and medium distances from the outcrop (up to 40 m), whereas the hare’s greatest
activity was recorded at distances greater than 50 m. However, there is a partial overlap at medium distances (30–40 m) among
both herbivores. Although, in general terms, there is no significant spatial overlap between hares and southern vizcachas,
their biological characteristics and the high dietary overlap between the species allow us to predict that, if resources become
scarce, the hare could extend its area of activity, as what happens elsewhere, and exploit food resources near outcrops, increasing
the vulnerability of vizcacha colonies. 相似文献