全文获取类型
收费全文 | 406篇 |
免费 | 45篇 |
出版年
2024年 | 1篇 |
2023年 | 11篇 |
2022年 | 6篇 |
2021年 | 8篇 |
2020年 | 15篇 |
2019年 | 4篇 |
2018年 | 14篇 |
2017年 | 21篇 |
2016年 | 22篇 |
2015年 | 33篇 |
2014年 | 49篇 |
2013年 | 32篇 |
2012年 | 43篇 |
2011年 | 36篇 |
2010年 | 25篇 |
2009年 | 21篇 |
2008年 | 19篇 |
2007年 | 13篇 |
2006年 | 8篇 |
2005年 | 6篇 |
2004年 | 7篇 |
2003年 | 5篇 |
2002年 | 7篇 |
2001年 | 5篇 |
2000年 | 10篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1994年 | 2篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 2篇 |
排序方式: 共有451条查询结果,搜索用时 31 毫秒
101.
The distribution of most recently discovered or described lemur species remains poorly known, but many appear to have small geographical ranges, making them vulnerable to extinction. Research can contribute to future conservation actions on behalf of these species by providing accurate information on local distribution and abundance. The distribution of the world’s smallest primate, the endangered Madame Berthe’s mouse lemur (Microcebus berthae), is limited to the Menabe Central region of western Madagascar. This species was discovered in the 1990s, but many fundamental aspects of its ecology remain unknown. The aims of our study were therefore to determine the actual distribution of Microcebus berthae across the forests of this region, to estimate population density, and to examine the species’ response to anthropogenic activities. We established 35 1-km line transects across Menabe Central, on which we surveyed mouse lemurs by distance sampling and live trapping. Microcebus berthae does not occur in all remaining forests of this small region and its population density is highly heterogeneous, both across its geographic range and locally. Within its area of occupancy, the population of Microcebus berthae not only was distributed according to spatial heterogeneities of the habitat, but also responded to anthropogenic disturbances and varied seasonally. Our results indicate that Microcebus berthae is susceptible to habitat degradation and avoids human environments spatially. As none of the forest remnants in which the species still occurs were officially protected until recently, immediate conservation actions should focus on effectively protecting Kirindy and Ambadira forests. 相似文献
102.
103.
Christina B. Karsten Falk F. R. Buettner Samanta Cajic Inga Nehlmeier Berit Neumann Antonina Klippert Ulrike Sauermann Udo Reichl Rita Gerardy-Schahn Erdmann Rapp Christiane Stahl-Hennig Stefan P?hlmann 《Journal of virology》2015,89(22):11727-11733
Human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) envelope (Env) proteins are extensively decorated with N-glycans, predominantly of the high-mannose type. However, it is unclear how high-mannose N-glycans on Env impact viral spread. We show that exclusive modification of SIV Env with these N-glycans reduces viral infectivity and abrogates mucosal transmission, despite increasing viral capture by immune cell lectins. Thus, high-mannose N-glycans have opposed effects on SIV infectivity and lectin reactivity, and a balance might be required for efficient mucosal transmission. 相似文献
104.
We introduce fast implementations for the likelihood functions, telemetry error filters, probabilistic trajectory and velocity reconstructions, and movement-path simulations for a large class of continuous-time movement models. This class of models includes all of the basic continuous-time models that have been applied to animal movement. A diverse array of movement behaviors can be modeled from within this framework, including range residence, persistence of motion, migration, range shifting, and territorial patrol. The fast algorithms presented here, based upon the Kálmán filter, are critical for applying movement analyses to the evergrowing number of modern datasets that feature thousands or more observed animal locations, and they are key to the continuous-time movement modeling (ctmm) R package. 相似文献
105.
It has been repeatedly shown that chronic stress changes dendrites, spines and modulates expression of synaptic molecules. These effects all may impair information transfer between neurons. The present study shows that chronic stress also regulates expression of M6a, a glycoprotein which is localised in axonal membranes. We have previously demonstrated that M6a is a component of glutamatergic axons. The present data reveal that it is the splice variant M6a-Ib, not M6a-Ia, which is strongly expressed in the brain. Chronic stress in male rats (3 weeks daily restraint) has regional effects: quantitative in situ hybridization demonstrated that M6a-Ib mRNA in dentate gyrus granule neurons and in CA3 pyramidal neurons is downregulated, whereas M6a-Ib mRNA in the medial prefrontal cortex is upregulated by chronic stress. This is the first study showing that expression of an axonal membrane molecule is differentially affected by stress in a region-dependent manner. Therefore, one may speculate that diminished expression of the glycoprotein in the hippocampus leads to altered output in the corresponding cortical projection areas. Enhanced M6a-Ib expression in the medial prefrontal cortex (in areas prelimbic and infralimbic cortex) might be interpreted as a compensatory mechanism in response to changes in axonal projections from the hippocampus. Our findings provide evidence that in addition to alterations in dendrites and spines chronic stress also changes the integrity of axons and may thus impair information transfer even between distant brain regions. 相似文献
106.
Andreas Koenig 《Primates; journal of primatology》1998,39(1):85-90
The rates of visual scanning and vocalizations were studied in a group of captive marmosets (Callinthrix jacchus) after the presentation of five different stimuli (artificial flower, playback of long calls, female/male conspecific, stuffed
wild cat) in order to assess the function of visual scanning. Only the presentation of a stuffed cat induced a significant
response. The adult males in particular increased their scanning rate and all adult individuals decreased their rate of vocalizations.
The results indicate that visual scanning in marmosets is an appropriate measure of vigilance which seems to serve the function
of predator detection and avoidance. The strong response of adult males suggests that they play a special role in predator
detection. 相似文献
107.
Relaxin in the marmoset monkey: secretion pattern in the ovarian cycle and early pregnancy. 总被引:5,自引:0,他引:5
A Einspanier R Nubbemeyer S Schlote M Schumacher R Ivell K Fuhrmann A Marten 《Biology of reproduction》1999,61(2):512-520
Relaxin is a peptide hormone with a broad range of biological activities, related not only to parturition and lactation but possibly also to decidualization, implantation, and early pregnancy. The present study was designed to investigate the secretion pattern of relaxin throughout the cycle and early pregnancy in the common marmoset monkey in relation to ovarian function and the systemic hormone milieu. First, a novel relaxin ELISA was developed and validated to confirm the pattern of relaxin secretion during pregnancy. Secondly, serum relaxin profiles were determined through nonconceptive and conceptive cycles and analyzed in relation to the concentration of other hormones and to the development of ovarian follicles and corpora lutea (CL). Blood samples were collected 2-3 times per week from the experimental animals and analyzed for relaxin, progesterone, and LH. The animals from the conceptive cycles were also ultrascanned at these time points to determine the ovarian status up to Day 25 of pregnancy. During early pregnancy, the relaxin levels in serum were approximately 1 ng/ml, increasing up to 15 ng/ml in the second trimester, at a time when progesterone levels had declined. In the third trimester, when progesterone levels were increasing again, the levels of relaxin decreased, returning to basal levels by term of pregnancy. In early pregnancy there was a parallel increase in both relaxin and LH/hCG, with the relaxin rise in the conceptive cycle appearing sooner than in the nonconceptive cycle, suggesting that, like chorionic gonadotropin (CG), relaxin may be a useful and early marker for pregnancy. Unlike the situation in the human, there was no correlation between the levels of either hormone and the number of CL detected, infants born, mother's age, or parity. Relaxin levels increased in early pregnancy before bioactive LH/CG, implying that relaxin is not directly regulated by this gonadotropin. Furthermore, hCG applied to nonconceptive females during the expected time of implantation caused an increase in progesterone but not in relaxin concentrations. In summary, the results obtained indicate that relaxin may be a reliable indicator of early pregnancy status in the common marmoset, but it is independent of direct CG influence. 相似文献
108.
Background
Comprehensive explanations of behavioral adaptations rarely invoke all levels famously admonished by Niko Tinbergen. The role of developmental processes and plasticity, in particular, has often been neglected. In this paper, we combine ecological, physiological and developmental perspectives in developing a hypothesis to account for the evolution of ‘the lemur syndrome’, a combination of reduced sexual dimorphism, even adult sex ratios, female dominance and mild genital masculinization characterizing group-living species in two families of Malagasy primates.Results
We review the different components of the lemur syndrome and compare it with similar adaptations reported for other mammals. We find support for the assertion that the lemur syndrome represents a unique set of integrated behavioral, demographic and morphological traits. We combine existing hypotheses about underlying adaptive function and proximate causation by adding a potential developmental mechanism linking maternal stress and filial masculinization, and outline an evolutionary scenario for its canalization.Conclusions
We propose a new hypothesis linking ecological, physiological, developmental and evolutionary processes to adumbrate a comprehensive explanation for the evolution of the lemur syndrome, whose assumptions and predictions can guide diverse future research on lemurs. This hypothesis should also encourage students of other behavioral phenomena to consider the potential role of developmental plasticity in evolutionary innovation.109.
Melanie Dammhahn 《International journal of primatology》2012,33(1):282-283
110.