全文获取类型
收费全文 | 1181篇 |
免费 | 7篇 |
出版年
2013年 | 22篇 |
2012年 | 16篇 |
2011年 | 24篇 |
2010年 | 42篇 |
2009年 | 52篇 |
2008年 | 48篇 |
2007年 | 58篇 |
2006年 | 38篇 |
2005年 | 35篇 |
2004年 | 23篇 |
2003年 | 9篇 |
2002年 | 7篇 |
1999年 | 9篇 |
1998年 | 19篇 |
1997年 | 20篇 |
1996年 | 25篇 |
1995年 | 8篇 |
1994年 | 13篇 |
1993年 | 14篇 |
1992年 | 21篇 |
1991年 | 25篇 |
1990年 | 12篇 |
1989年 | 28篇 |
1988年 | 24篇 |
1987年 | 25篇 |
1986年 | 18篇 |
1985年 | 22篇 |
1984年 | 22篇 |
1983年 | 22篇 |
1982年 | 11篇 |
1981年 | 20篇 |
1980年 | 7篇 |
1979年 | 24篇 |
1978年 | 26篇 |
1977年 | 22篇 |
1976年 | 13篇 |
1975年 | 25篇 |
1974年 | 26篇 |
1973年 | 29篇 |
1972年 | 45篇 |
1971年 | 47篇 |
1970年 | 9篇 |
1969年 | 16篇 |
1968年 | 14篇 |
1967年 | 12篇 |
1966年 | 12篇 |
1965年 | 10篇 |
1959年 | 11篇 |
1958年 | 7篇 |
1954年 | 11篇 |
排序方式: 共有1188条查询结果,搜索用时 109 毫秒
81.
Abstract. 1. Predators, including insect parasitoids, often eavesdrop on prey signals, and as a result, predation can have important effects on the evolution of prey signalling behaviour.
2. The phonotactic parasitoid fly, Ormia ochracea , uses the calling songs of male field crickets to locate their field crickets hosts. In the western USA, this fly parasitises the variable field cricket, Gryllus lineaticeps . Previous work with one fly population suggested that female flies, like female field crickets, preferentially orient to male songs with higher chirp rates and longer chirp durations, although a limited range of male song types was used in this previous study. The current study, with a different fly population, used field-based, two-speaker choice tests to examine: (1) the effect of male chirp rate and chirp duration on fly attraction, using a natural range of song types; and (2) the relative importance of these song types in host selection by the flies.
3. Three lines of evidence suggested that chirp rate is more important than chirp duration in host selection. (a) The flies consistently preferred higher chirp rates but only sometimes preferred longer chirp durations. (b) The flies consistently preferred higher chirp rate/shorter chirp duration songs to lower chirp rate/longer chirp duration songs. (c) Preferences for longer chirp durations could be eliminated by increasing the amplitude of the less attractive song type, while preferences for higher chirp rates could only sometimes be eliminated by increasing the amplitude of the less attractive song type.
4. Fly predation may favour lower chirp rates and shorter chirp durations in G. lineaticeps , and may have resulted in stronger selection on chirp rate than on chirp duration. 相似文献
2. The phonotactic parasitoid fly, Ormia ochracea , uses the calling songs of male field crickets to locate their field crickets hosts. In the western USA, this fly parasitises the variable field cricket, Gryllus lineaticeps . Previous work with one fly population suggested that female flies, like female field crickets, preferentially orient to male songs with higher chirp rates and longer chirp durations, although a limited range of male song types was used in this previous study. The current study, with a different fly population, used field-based, two-speaker choice tests to examine: (1) the effect of male chirp rate and chirp duration on fly attraction, using a natural range of song types; and (2) the relative importance of these song types in host selection by the flies.
3. Three lines of evidence suggested that chirp rate is more important than chirp duration in host selection. (a) The flies consistently preferred higher chirp rates but only sometimes preferred longer chirp durations. (b) The flies consistently preferred higher chirp rate/shorter chirp duration songs to lower chirp rate/longer chirp duration songs. (c) Preferences for longer chirp durations could be eliminated by increasing the amplitude of the less attractive song type, while preferences for higher chirp rates could only sometimes be eliminated by increasing the amplitude of the less attractive song type.
4. Fly predation may favour lower chirp rates and shorter chirp durations in G. lineaticeps , and may have resulted in stronger selection on chirp rate than on chirp duration. 相似文献
82.
83.
84.
BRANT C. FAIRCLOTH GWEN P. KELLER C. JOSEPH NAIRN WILLIAM E. PALMER JOHN P. CARROLL PATRICIA ADAIR GOWATY 《Molecular ecology resources》2006,6(3):646-649
We describe primers and polymerase chain reaction (PCR) conditions to amplify 18 tetranucleotide microsatellite DNA loci in eastern bluebirds (Sialia sialis). The primers were tested using individuals from two study sites in Georgia and South Carolina. Among individuals from the Georgia population (n = 23), the primer pairs developed in this study yielded an average of 6.6 alleles per locus (range 2–12), an average observed heterozygosity of 0.56 (range 0.24–0.96) and an average polymorphic information content of 0.65 (range 0.3–0.86). Among individuals from the South Carolina population (n = 19), the primer pairs yielded an average of 5.8 alleles per locus (range 2–9), an average observed heterozygosity of 0.56 (range 0.05–0.86) and an average polymorphic information content of 0.63 (range 0.29–0.83). 相似文献
85.
We report on the use of infrared‐triggered cameras as an effective tool to survey phasianid populations in Wanglang and Wolong Nature Reserves, China. Surveys at 183 camera‐trapping sites recorded 30 bird species, including nine phasianids (one grouse and eight pheasant species). Blood Pheasant Ithaginis cruentus and Temminck’s Tragopan Tragopan temminckii were the phasianids most often detected at both reserves and were found within the mid‐elevation range (2400–3600 m asl). The occupancy rate and detection probability of both species were examined using an occupancy model relative to eight sampling covariates and three detection covariates. The model estimates of occupancy for Blood Pheasant (0.30) and Temminck’s Tragopan (0.14) are close to the naïve estimates based on camera detections (0.27 and 0.13, respectively). The estimated detection probability during a 5‐day period was 0.36 for Blood Pheasant and 0.30 for Temminck’s Tragopan. The daily activity patterns for these two species were assessed from the time/date stamps on the photographs and sex ratios calculated for Blood Pheasant (152M : 72F) and Temminck’s Tragopan (48M : 21F). Infrared cameras are valuable for surveying these reclusive species and our protocol is applicable to research or monitoring of phasianids. 相似文献
86.
Spatial and temporal variation in prey abundance have been shown to impact the time of breeding and breeding success of birds. Understanding the ecological requirements of preferred prey can help develop management measures to improve food supply for target species. For the colonial Lesser Kestrel Falco naumanni, mole crickets Gryllotalpa spp. are one of the most important prey items during the mate‐feeding period. Lesser Kestrel colonies with higher mole cricket consumption had earlier egg‐laying dates, suggesting that differences between individuals in the time of breeding could be caused by differences in the diet. Moreover, the mean number of mole crickets in pellets was significantly correlated with clutch size (in one of the studied years) and egg volume. Thus, the impact of environmental variables and land use on mole crickets is likely to be relevant to Lesser Kestrel conservation. Weekly consumption of mole crickets was higher following an increase in either precipitation or minimum temperature values. Furthermore, mole cricket consumption was higher in colonies surrounded by higher quality soils and in wetter areas and years. Predicted probability of mole cricket occurrence in surveyed watercourse margins suggested a positive relationship between soil penetrability and mole cricket occurrence. Among variables that might be the target of management, the presence of riparian vegetation positively influenced the occurrence of mole crickets, whilst tillage and sowing of streambeds were revealed as the most important threats. We suggest that the maintenance of native vegetation in the margins of watercourses could improve soil resilience to erosion, increase water retention, soil penetrability and fertility, and provide a food supply and shelter for mole crickets. Overall, the implementation of such recommendations is likely to benefit other farmland species known to consume mole crickets, including several endangered species. 相似文献
87.
JAMES E. LYONS MICHAEL C. RUNGE HAROLD P. LASKOWSKI WILLIAM L. KENDALL 《The Journal of wildlife management》2008,72(8):1683-1692
Abstract: In a natural resource management setting, monitoring is a crucial component of an informed process for making decisions, and monitoring design should be driven by the decision context and associated uncertainties. Monitoring itself can play ≥3 roles. First, it is important for state-dependent decision-making, as when managers need to know the system state before deciding on the appropriate course of action during the ensuing management cycle. Second, monitoring is critical for evaluating the effectiveness of management actions relative to objectives. Third, in an adaptive management setting, monitoring provides the feedback loop for learning about the system; learning is sought not for its own sake but primarily to better achieve management objectives. In this case, monitoring should be designed to reduce the critical uncertainties in models of the managed system. The United States Geological Survey and United States Fish and Wildlife Service are conducting a large-scale management experiment on 23 National Wildlife Refuges across the Northeast and Midwest Regions. The primary management objective is to provide habitat for migratory waterbirds, particularly during migration, using water-level manipulations in managed wetlands. Key uncertainties are related to the potential trade-offs created by management for a specific waterbird guild (e.g., migratory shorebirds) and the response of waterbirds, plant communities, and invertebrates to specific experimental hydroperiods. We reviewed the monitoring program associated with this study, and the ways that specific observations fill ≥1 of the roles identified above. We used observations from our monitoring to improve state-dependent decisions to control undesired plants, to evaluate management performance relative to shallow-water habitat objectives, and to evaluate potential trade-offs between waterfowl and shorebird habitat management. With limited staff and budgets, management agencies need efficient monitoring programs that are used for decision-making, not comprehensive studies that elucidate all manner of ecological relationships. 相似文献
88.
BRETT K. SANDERCOCK WILLIAM E. JENSEN CHRISTOPHER K. WILLIAMS ROGER D. APPLEGATE 《The Journal of wildlife management》2008,72(4):970-982
Abstract: The northern bobwhite (Colinus virginianus) is an economically important gamebird that is currently undergoing widespread population declines. Despite considerable research on the population ecology of bobwhites, there have been few attempts to model population dynamics of bobwhites to determine the contributions of different demographic parameters to variance of the finite rate of population change (Λ). We conducted a literature review and compiled 405 estimates of 9 demographic parameters from 49 field studies of bobwhites. To identify demographic parameters that might be important for management, we used life-stage simulation analyses (LSA) to examine sensitivity of Λ to simulated variation in 9 demographic parameters for female bobwhites. In a baseline LSA based on uniform distributions bounded by the range of estimates for each demographic parameter, bobwhite populations were predicted to decline (Λ = 0.56) and winter survival of adults made the greatest contribution to variance of Λ (r2 = 0.453), followed by summer survival of adults (r2 = 0.163), and survival of chicks (r2 = 0.120). Population change was not sensitive to total clutch laid, nest survival, egg hatchability, or 3 parameters associated with the number of nesting attempts (r2<0.06). Our conclusions were robust to alternative simulation scenarios, and parameter rankings changed only if we adjusted the lower bounds of winter survival upwards. Bobwhite populations were not viable with survival rates reported from most field studies. Survival rates may be depressed below sustainable levels by environmental conditions or possibly by impacts of capture and telemetry methods. Overall, our simulation results indicate that management practices that improve seasonal survival rates will have the greatest potential benefit for recovery of declining populations of bobwhites. 相似文献
89.
SARAH R. HURTEAU THOMAS D. SISK WILLIAM M. BLOCK BRETT G. DICKSON 《The Journal of wildlife management》2008,72(5):1168-1174
Abstract: We assessed responses of the breeding bird community to mechanical thinning and prescribed surface fire, alone and in combination, between 2000 and 2006 in ponderosa pine (Pinus ponderosa) forests in northern Arizona, USA. Fuel-reduction treatments did not affect species richness or evenness, and effects on density of 5 commonly detected species varied among species. Populations of some species, such as the western bluebird (Sialia mexicana), increased following burning treatments, whereas others, such as the mountain chickadee (Poecile gambeli), decreased in response to thinning treatments. Our results also identified a temporal response component, where avian community composition and structure changed synchronously on all treatments over time. Given the modest effects these small-scale fuel-reduction treatments had on avian composition and the specific density responses of particular species, our results suggest that land managers should consider implementing prescribed surface fire after thinning projects, where appropriate. 相似文献
90.
ELENA V. BUZAN BORIS KRYSTUFEK BERND HÄNFLING WILLIAM F. HUTCHINSON 《Biological journal of the Linnean Society. Linnean Society of London》2008,94(4):825-835
Comprehensive taxonomic sampling can vastly improve the accuracy of phylogenetic reconstruction. Here, we present the most inclusive phylogenetic analysis of Arvicolinae (Mammalia, Rodentia) to date, combining all published cytochrome b gene sequences of greater than 1097 bp and new sequences from two monotypic genera. Overall, the phylogenetic relationships between 69 species of voles and lemmings, representing 18 genera and 10 tribes, were studied. By applying powerful modern approaches to phylogenetic reconstruction, such as maximum likelihood and Bayesian analysis, we provide new information on the early pulse of evolution within the Arvicolinae. While the position of two highly divergent lineages, Phenacomys and Ondatra , could not be resolved, the tribe Lemmini, appeared as the most basal group of voles. The collared lemmings (Dicrostonychini) grouped together with all of the remaining tribes. The two previously unstudied monotypic genera Dinaromys and Prometheomys form a moderately well-supported monophyletic clade, possibly a sister group to Ellobius (Ellobiusini). Furthermore, with one exception, all tribes ( sensu Musser & Carleton, 2005) proved to be monophyletic and can thus be regarded as meaningful evolutionary entities. Only the tribe Arvicolini emerged as paraphyletic in both analyses because of the unresolved phylogenetic position of Arvicola terrestris . Steppe voles of the genus Lagurus were solidly supported as a sister group to the Microtus and allies clade. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 825–835. 相似文献