全文获取类型
收费全文 | 165篇 |
免费 | 15篇 |
出版年
2022年 | 2篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 6篇 |
2017年 | 3篇 |
2016年 | 6篇 |
2015年 | 8篇 |
2014年 | 8篇 |
2013年 | 10篇 |
2012年 | 8篇 |
2011年 | 12篇 |
2010年 | 5篇 |
2009年 | 7篇 |
2008年 | 5篇 |
2007年 | 17篇 |
2006年 | 7篇 |
2005年 | 10篇 |
2004年 | 9篇 |
2003年 | 10篇 |
2002年 | 12篇 |
2001年 | 5篇 |
1999年 | 1篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有180条查询结果,搜索用时 487 毫秒
21.
Cathleen Wigand Randy Comeleo Richard McKinney Glen Thursby Marnita Chintala Micheal charpentier 《人类与生态风险评估》2001,7(5):1541-1554
The integrity of coastal salt marshes can be determined from the extent to which they provide key ecosystem services: food and habitat for fish and wildlife, good water quality, erosion and flood control, and recreation and cultural use. An outline of a new approach for linking ecosystem services with metrics of structure and function to evaluate the ecological integrity of salt marshes is described. One main objective of the approach is to determine whether differences in structure and function can be detected among salt marshes with similar geomorphology and hydrology but different degrees of anthropogenic stress. The approach is currently being applied to salt marshes of Narragansett Bay, RI, USA. Stable nitrogen isotopic ratios of the marsh biota reflected the nitrogen sources from the adjacent watersheds and were significantly correlated with percent residential land use. Results show that plant zonation significantly ( r = —0.82; p < 0.05) relates with percent residential land use and is potentially a sensitive indicator of anthropogenic disturbance of New England salt marshes. We are currently examining species diversity, denitrification rates, and susceptibility to erosion among the sites for additional indicators of salt marsh condition. Our results to date suggest that this approach will provide the methods needed for managers to systematically monitor and evaluate the integrity of salt marshes 相似文献
22.
Long-term studies of urban birds are relatively scarce, especially in Africa. We analysed trends in species richness and bird species occurrence over a 32-year period in Kampala, Uganda, in order to assess changes in the bird community in a period that has shown rapid expansion of the city's human population. Given that species may respond to urbanisation according to their diet, we also analysed bird community trends of species groups defined according to predominant diet. There was an overall decline in species richness that was largely driven by declines in insectivores and granivores. General declines were evident also when the trends in the most common individual species in these two groups were considered. The occurrence of the commonest predator and scavenger species tended to increase over the period considered. Insectivorous species are likely to be especially affected by increasing urbanisation due to air pollution. Predators and scavengers are likely to have benefitted from the inability of municipal waste management to keep pace with growth in the human population, hence providing more potential food resources. Both insectivores and predators/scavengers are therefore good candidates for the development of urban indicators. 相似文献
23.
24.
Reducing a CO to a CH2 moiety in a peptide bond destroys the ability of the peptide link to act as a proton acceptor in a hydrogen-bonded structure. Here, this modification is introduced into different positions of the helical peptide, acetyl-WGG(RAAAA)4R-amide, and the melting of these peptides is followed using CD. Effects of this modification on helical peptides are compared to our previous N-methylation studies [C. F. Chang and M.H. Zehfus (1996) Biopolymers, Vol. 40, pp. 609–616]. While the experiments were designed to remove the same hydrogen bond from the peptide, no consistent results are obtained between these two modifications. This result suggests that these modifications not only break the backbone hydrogen bonds, but also involve other destabilizing effects. When our data is analyzed using different helix-coil transition models, the results show that as the models increase in complexity the energy associated with a single residue modification increases. Unfortunately, the most detailed dichroic model, which should best describe this system, works for only one peptide. Apparently, the models need to be further improved to better mimic our system. © 1998 John Wiley & Sons, Inc. Biopoly 46: 181–193, 1998 相似文献
25.
Brood size manipulations reveal relationships among physiological performance,body condition and plumage colour in Northern Flicker Colaptes auratus nestlings
下载免费PDF全文
![点击此处可从《Ibis》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Visual signals of quality in offspring, such as plumage colour, should honestly advertise need and/or body condition, but links between nutritional status, physiological performance and the expression of colours are complex and poorly understood. We assess how food stress during rearing affected two physiological measures (T‐cell‐mediated immune function and corticosterone level in feathers: CORTf) and how these two variables were related to carotenoid and melanin coloration in Northern Flicker Colaptes auratus nestlings. We were also interested in how these two physiological measures were influenced by the sex of the nestling. We experimentally manipulated brood size to alter levels of food availability to nestlings during development. We measured carotenoid‐based colour (chroma and brightness) in wing feathers and the size of melanin spots on breast feathers. In agreement with our prediction, nestlings in the reduced brood treatment had better body condition and stronger immune responses than those in the control and brood enlargement treatments. This supports the hypothesis that immune responses are energetically costly. In contrast, CORTf was not related to nestling body condition or sex and was unaffected by brood size manipulation. Nestlings of both sexes with stronger T‐cell‐mediated immune responses had larger melanin spots but only males with higher immune responses also had brighter flight feathers. Feather brightness decreased with increasing CORTf levels. Our study is one of the few to examine the relationship between multiple physiological and plumage measures in nestlings and shows that plumage colour and immune function signalled body condition of nestlings, but that feather corticosterone levels did not. 相似文献
26.
27.
Kelly E. Radziwon Kristie M. June Daniel J. Stolzberg Matthew A. Xu-Friedman Richard J. Salvi Micheal L. Dent 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2009,195(10):961-969
Tone detection and temporal gap detection thresholds were determined in CBA/CaJ mice using a Go/No-go procedure and the psychophysical
method of constant stimuli. In the first experiment, audiograms were constructed for five CBA/CaJ mice. Thresholds were obtained
for eight pure tones ranging in frequency from 1 to 42 kHz. Audiograms showed peak sensitivity between 8 and 24 kHz, with
higher thresholds at lower and higher frequencies. In the second experiment, thresholds for gap detection in broadband and
narrowband noise bursts were measured at several sensation levels. For broadband noise, gap thresholds were between 1 and
2 ms, except at very low sensation levels, where thresholds increased significantly. Gap thresholds also increased significantly
for low pass-filtered noise bursts with a cutoff frequency below 18 kHz. Our experiments revised absolute auditory thresholds
in the CBA/CaJ mouse strain and demonstrated excellent gap detection ability in the mouse. These results add to the baseline
behavioral data from normal-hearing mice which have become increasingly important for assessing auditory abilities in genetically
altered mice. 相似文献
28.
Absolute protein quantification by LC/MS(E) for global analysis of salicylic acid-induced plant protein secretion responses 总被引:1,自引:0,他引:1
The plant cell wall is a dynamic cellular compartment consisting of a complex matrix of components that can change dramatically in response to environmental stresses. During pathogen attack, for instance, a wide spectrum of proteins that participate in various sequential processes involved in plant defense is secreted into the cell wall. In this study, a mass spectrometry, data-independent acquisition approach known as LC/MS (E) was used to assess temporal changes in the cell wall proteome in response to different levels of an endogenous inducer of plant disease defense responses, salicylic acid (SA). LC/MS (E) was used as a label-free method that enabled simultaneous protein identification and absolute femtomole quantification of each protein secreted into the extracellular matrix. A total of 74 secreted proteins were identified, 63 of which showed increased specific secretion in response to SA. A majority of this induced secretion occurred within 2 h of treatment, indicating that many proteins are involved in the early stages of plant defenses. We also identified a number of apparently nonclassically secreted proteins, suggesting that, as in many nonplant systems, Golgi/ER-independent mechanisms exist for plant protein secretion. These results provide new insight into plant apoplastic defense mechanisms and demonstrate that LC/MS (E) is a powerful tool for obtaining both relative and absolute proteome-scale quantification that can be applied to complex, time- and dose-dependent experimental designs. 相似文献
29.
Current advancements in the study of the theoretical basis of species interactions are helping scientists understand the basic parameters governing the dynamics of the interactions between generalist herbivores and their target plants. In practice, however, both inter- and intra-specific interactions between plants (as well as between herbivores and plants) within multispecies systems that are under the influence of interrelated biotic and abiotic variables are difficult to predict. Here, we discuss our findings on the effect of simulated herbivory on Mimosa pigra L. leaves on seedling survivability. In Malaysia, M. pigra, a semi-aquatic invasive plant introduced from the South American region, is already creating an ecological problem, especially in wetland habitats. To better understand the impact of herbivores on the M. pigra population, a simulated experiment of the herbivory effect on Mimosa seedlings was conducted. This experiment combined two treatments of simulated herbivory on the leaves of established Mimosa seedlings, that is, a two-level intensity treatment (50 and 100 % defoliation) and a seven-level frequency treatment (one to seven defoliations). The data suggest that Mimosa is highly resilient against herbivory. This plant was able to compensate for repeated losses, thus suggesting that the introduction of herbivores in an effort to totally eradicate the Mimosa population is unlikely to be successful. 相似文献
30.
William Burchill Dejun Li Gary J. Lanigan Micheal Williams James Humphreys 《Global Change Biology》2014,20(10):3137-3146
Nitrous oxide (N2O) emissions are subject to intra‐ and interannual variation due to changes in weather and management. This creates significant uncertainties when quantifying estimates of annual N2O emissions from grazed grasslands. Despite these uncertainties, the majority of studies are short‐term in nature (<1 year) and as a consequence, there is a lack of data on interannual variation in N2O emissions. The objectives of this study were to (i) quantify annual N2O emissions and (ii) assess the causes of interannual variation in emissions from grazed perennial ryegrass/white clover grassland. Nitrous oxide emissions were measured from fertilized and grazed perennial ryegrass/white clover grassland (WC) and from perennial ryegrass plots that were not grazed and did not receive N input (GB), over 4 years from 2008 to 2012 in Ireland (52°51′N, 08°21′W). The annual N2O‐N emissions (kg ha?1; mean ± SE) ranged from 4.4 ± 0.2 to 34.4 ± 5.5 from WC and from 1.7 ± 0.8 to 6.3 ± 1.2 from GB. Interannual variation in N2O emissions was attributed to differences in annual rainfall, monthly (December) soil temperatures and variation in N input. Such substantial interannual variation in N2O emissions highlights the need for long‐term studies of emissions from managed pastoral systems. 相似文献