首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   4690篇
  免费   442篇
  国内免费   4篇
  2023年   41篇
  2022年   83篇
  2021年   174篇
  2020年   110篇
  2019年   117篇
  2018年   135篇
  2017年   127篇
  2016年   173篇
  2015年   291篇
  2014年   303篇
  2013年   295篇
  2012年   442篇
  2011年   432篇
  2010年   217篇
  2009年   212篇
  2008年   289篇
  2007年   257篇
  2006年   233篇
  2005年   208篇
  2004年   180篇
  2003年   147篇
  2002年   121篇
  2001年   31篇
  2000年   16篇
  1999年   22篇
  1998年   27篇
  1997年   19篇
  1996年   20篇
  1995年   17篇
  1994年   14篇
  1993年   15篇
  1992年   19篇
  1991年   15篇
  1990年   14篇
  1989年   18篇
  1988年   12篇
  1987年   12篇
  1986年   12篇
  1985年   16篇
  1984年   11篇
  1983年   11篇
  1982年   14篇
  1981年   19篇
  1980年   12篇
  1979年   18篇
  1977年   14篇
  1976年   12篇
  1975年   12篇
  1974年   13篇
  1964年   9篇
排序方式: 共有5136条查询结果,搜索用时 163 毫秒
191.
In anthropology, the body is theorized, manifested, and experienced in multiple ways that impact medical practice, social life, biopolitics, and spirituality. This article considers the role of ‘dreadlocks’ (matted hair) in the Rastafari spiritual body and, guided by the ‘body multiple’ concept, explores how the symbolic and performative nature of hair articulates with age and gender. Ethnographic data from the United Kingdom suggest the ways dreadlocks are groomed and/or covered vary widely, revealing diversity and changing meanings attributed to matted hair. By focusing on the spiritual aspects of hair, our work shows that dreadlocks and baldness are outward (visible) and inward (hidden) manifestations of a covenant with Jah (the Creator), rather than contrasting social or psychological statements. The hair symbolism debate in anthropology reveals limitations of universalist and reductionist approaches to understanding the human body. Our Rastafari material suggests the body multiple provides a better framework for interpreting (African-inspired) spiritual hair.  相似文献   
192.
Ecosystems - A major functional division in ectomycorrhizal fungi is between taxa with hydrophobic ectomycorrhizae (strong proteolytic capabilities, deep nitrogen (N) acquisition, and extensive...  相似文献   
193.
Our understanding of the evolutionary stability of socially selected traits is dominated by sexual selection models originating with R. A. Fisher, in which genetic covariance arising through assortative mating can trigger exponential, runaway trait evolution. To examine whether nonreproductive, socially selected traits experience similar dynamics—social runaway—when assortative mating does not automatically generate a covariance, we modeled the evolution of socially selected badge and donation phenotypes incorporating indirect genetic effects (IGEs) arising from the social environment. We establish a social runaway criterion based on the interaction coefficient, ψ , which describes social effects on badge and donation traits. Our models make several predictions. (1) IGEs can drive the original evolution of altruistic interactions that depend on receiver badges. (2) Donation traits are more likely to be susceptible to IGEs than badge traits. (3) Runaway dynamics in nonsexual, social contexts can occur in the absence of a genetic covariance. (4) Traits elaborated by social runaway are more likely to involve reciprocal, but nonsymmetrical, social plasticity. Models incorporating plasticity to the social environment via IGEs illustrate conditions favoring social runaway, describe a mechanism underlying the origins of costly traits, such as altruism, and support a fundamental role for phenotypic plasticity in rapid social evolution.  相似文献   
194.
For more than a century, the Boone and Crockett Club has kept records of harvest locations for 38 categories of North American big game, which includes measurement details and sizes of enduring characteristics (e.g., antlers, skulls, horns). All white-tailed deer (Odocoileus virginianus) entered in the Club records (i.e., record deer) have large antlers because the measurements must meet or exceed a minimum size to qualify for entry. We used the records from the Club to test the hypothesis that the spatial distribution in the harvest of record deer was related to the number of antlered deer harvested, variations in land productivity, soil mineral content, and attributes of land cover for 9 states in the midwestern United States. We used a Bayesian theoretical framework to develop a spatial model that examined the influence of explanatory variables on the number of record deer harvested in each county. In our study area, 3,658 record deer were harvested in 692 of the 856 counties (80.8%). More record deer were harvested in counties that had more high-contrast edges, less contiguous land cover, and greater variation in soil productivity. These results provide information for managers and hunters to better understand the spatial distribution of record deer and factors that are correlated with their distribution. © 2019 The Wildlife Society.  相似文献   
195.
Species are considered conservation-reliant when their continued existence is dependent on human assistance. Conservation reliance challenges the conservation community in terms of their ability to sustain the funding and public-private partnerships needed for indefinite management. Although increased funding for conservation is critical, reducing conservation reliance through adaptive management represents an attractive alternative. We used a large-scale ecological experiment as a case study in the use of adaptive management to reduce conservation reliance. For >40 years, the United States Fish and Wildlife Service has trapped and lethally removed an obligate brood parasite, the brown-headed cowbird (Molothrus ater), to protect the Kirtland's warbler (Setophaga kirtlandii) from the negative effects that brood parasitism has on its reproductive success. To determine if the conservation reliance of the Kirtland's warbler could be reduced through optimization of the cowbird control program, we used an adaptive management approach. In collaboration with stakeholders, we experimentally reduced cowbird trapping effort across nearly all of the Kirtland's warbler breeding range. We monitored the resulting cowbird abundance and rate of parasitism, and then adjusted the scale of trap reductions based on the previous year's results. Despite reducing (2015–2017) and eventually eliminating (2018) cowbird trapping, we detected only 20 cowbirds (2015–2017) and found that just 4 of 514 (<1%) nests were parasitized (2015–2018). Our results indicate that the cowbird control program can at least temporarily be suspended, thereby reducing conservation reliance in the Kirtland's warbler and freeing funds for other management. We urge the conservation community to consider the use of adaptive management to reduce conservation reliance in other threatened and endangered taxa. © 2019 The Wildlife Society.  相似文献   
196.
197.
Cross-contamination of epidermal mucus was assessed at three sampling locations on the bodies of Pacific halibut Hippoglossus stenolepis by inducing contact between fish coated with labelled synthetic mucus and non-treated fish. Results indicate a positive relationship between sampling site exposure and sample contamination and that mucous sample cross-contamination can be mitigated by sampling in a location protected from external contact.  相似文献   
198.
We used mitochondrial DNA to assess the genetic structure of endangered lake chubsucker Erimyzon sucetta across its Canadian range. We found unique mitochondrial haplotypes in Lyons Creek, a tributary of the Niagara River that faces a strong potential for habitat deterioration. Lyons Creek may therefore serve as a reservoir of unique genetic diversity. The sensitivity of Lyons Creek, combined with the genetic uniqueness of its E. sucetta population, call for further investigation into whether this population should be considered a separate designatable unit for conservation purposes.  相似文献   
199.
200.
We estimated the daily age and growth of wild age‐0 alligator gar (Atractosteus spatula) from Choke Canyon Reservoir and the Guadalupe and Trinity rivers, Texas, USA. Growth rates of wild age‐0 alligator gar were compared across systems, as well as to alligator gar reared in a Texas hatchery. Estimated ages of alligator gar ranged from 7 to 80 days in Choke Canyon Reservoir (n = 140), 11–73 days in the Guadalupe River (n = 16), and 4–115 days in the Trinity River samples (n = 245). Alligator gar growth was faster in the Trinity and Guadalupe rivers than growth in Choke Canyon Reservoir. Growth of alligator gar in Choke Canyon Reservoir (3.60 ± 0.08 mm/day), the Guadalupe River (4.76 ± 0.35 mm/day), and the Trinity River (5.13 ± 0.07 mm/day) was faster than growth of hatchery reared fish (3.41 ± 0.08 mm/day). This study represents the first account of early growth of age‐0 alligator gar in the wild, and documents some of the fastest growth of age‐0 fish among freshwater fishes. We attribute the rapid growth of wild alligator gar to their quick transition to piscivory at early stages, and their effective use of habitat and resources on inundated floodplains during flood pulses. Future studies should explore the effects of environmental factors on the hatching success, growth, and survival of age‐0 alligator gar.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号