全文获取类型
收费全文 | 78篇 |
免费 | 11篇 |
专业分类
89篇 |
出版年
2023年 | 1篇 |
2019年 | 2篇 |
2016年 | 3篇 |
2015年 | 4篇 |
2014年 | 5篇 |
2013年 | 9篇 |
2012年 | 6篇 |
2011年 | 5篇 |
2010年 | 4篇 |
2008年 | 7篇 |
2007年 | 2篇 |
2006年 | 4篇 |
2005年 | 3篇 |
2004年 | 2篇 |
2003年 | 1篇 |
2002年 | 1篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1982年 | 2篇 |
1978年 | 1篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 2篇 |
排序方式: 共有89条查询结果,搜索用时 10 毫秒
1.
2.
Carmen Martínez José A Molina Hortensia Alonso-Navarro Félix J Jiménez-Jiménez José AG Agúndez Elena García-Martín 《BMC neurology》2010,10(1):71
Background
Human serum paraoxonase 1 (PON1) plays a major role in the metabolism of several organophosphorus compounds. The enzyme is encoded by the polymorphic gene PON1, located on chromosome 7q21.3. Aiming to identify genetic variations related to the risk of developing brain tumors, we investigated the putative association between common nonsynonymous PON1 polymorphisms and the risk of developing astrocytoma and meningioma. 相似文献3.
A guideline for ecological risk management procedures 总被引:1,自引:0,他引:1
Axel G. Rossberg Hiroyuki Matsuda Fumito Koike Takashi Amemiya Mitsutaku Makino Mari Morino Takashi Kubo Shinji Shimode Satoshi Nakai Mineo Katoh Tadayoshi Shigeoka Kohei Urano 《Landscape and Ecological Engineering》2005,1(2):221-228
A practical guideline for community-level ecological risk management is proposed, with particular emphasis on the mutual interdependencies of the scientific analysis, public consensus building, and an adaptive management. The procedure we recommend spans the screening of potential ecological risks, the involvement of related stakeholders, the conceptual development from the undesired event over assessment endpoints to measures of effect and stress factors, the risk assessment for the no-action case, the planning phase from the public decision to become active and the setting of goals over a specification of monitoring and control methods to an assessment of feasibility and a public approval of the management plan and finally the adaptive management from initiation over continued monitoring to revisions of the plan, if required. The procedure contains several checkpoints, alternative routes, and possibilities to correct previous decisions. 相似文献
4.
Contrasting changes in the abundance and diversity of North American bird assemblages from 1971 to 2010
下载免费PDF全文
![点击此处可从《Global Change Biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Aafke M. Schipper Jonathan Belmaker Murilo Dantas de Miranda Laetitia M. Navarro Katrin Böhning‐Gaese Mark J. Costello Maria Dornelas Ruud Foppen Joaquín Hortal Mark A. J. Huijbregts Berta Martín‐López Nathalie Pettorelli Cibele Queiroz Axel G. Rossberg Luca Santini Katja Schiffers Zoran J. N. Steinmann Piero Visconti Carlo Rondinini Henrique M. Pereira 《Global Change Biology》2016,22(12):3948-3959
Although it is generally recognized that global biodiversity is declining, few studies have examined long‐term changes in multiple biodiversity dimensions simultaneously. In this study, we quantified and compared temporal changes in the abundance, taxonomic diversity, functional diversity, and phylogenetic diversity of bird assemblages, using roadside monitoring data of the North American Breeding Bird Survey from 1971 to 2010. We calculated 12 abundance and diversity metrics based on 5‐year average abundances of 519 species for each of 768 monitoring routes. We did this for all bird species together as well as for four subgroups based on breeding habitat affinity (grassland, woodland, wetland, and shrubland breeders). The majority of the biodiversity metrics increased or remained constant over the study period, whereas the overall abundance of birds showed a pronounced decrease, primarily driven by declines of the most abundant species. These results highlight how stable or even increasing metrics of taxonomic, functional, or phylogenetic diversity may occur in parallel with substantial losses of individuals. We further found that patterns of change differed among the species subgroups, with both abundance and diversity increasing for woodland birds and decreasing for grassland breeders. The contrasting changes between abundance and diversity and among the breeding habitat groups underscore the relevance of a multifaceted approach to measuring biodiversity change. Our findings further stress the importance of monitoring the overall abundance of individuals in addition to metrics of taxonomic, functional, or phylogenetic diversity, thus confirming the importance of population abundance as an essential biodiversity variable. 相似文献
5.
A key problem in community ecology is to understand how individual-level traits give rise to population-level trophic interactions.
Here, we propose a synthetic framework based on ecological considerations to address this question systematically. We derive
a general functional form for the dependence of trophic interaction coefficients on trophically relevant quantitative traits
of consumers and resources. The derived expression encompasses—and thus allows a unified comparison of—several functional
forms previously proposed in the literature. Furthermore, we show how a community’s, potentially low-dimens ional, effective
trophic niche space is related to its higher-dimensional phenotypic trait space. In this manner, we give ecological meaning
to the notion of the “dimensionality of trophic niche space.” Our framework implies a method for directly measuring this dimensionality.
We suggest a procedure for estimating the relevant parameters from empirical data and for verifying that such data matches
the assumptions underlying our derivation. 相似文献
6.
Paul S Marley Aboubacar Toure Jay Shebayan DA Aba AO Toure AG Diallo 《Archives Of Phytopathology And Plant Protection》2013,46(1):29-34
Fourteen elite sorghum lines were evaluated for their resistance to Striga hermonthica at three locations in Nigeria and Mali. Results showed that many of the lines especially MALISOR 84-1, SAMSORG 41, 97-SB-F5DT-64 (Keninkédié) and the check SRN 39 remained resistant to Striga in all locations with low emerged Striga counts, while SAMSORG 14 had the highest Striga infestation in all locations. Considerable variation in reaction to Striga infestation was observed on Séguètana, 97-SB-F5DT-63 (Wasa), 97-SB-F5DT-65, CMDT 38, CMDT 39 and CMDT 45 which were susceptible to Striga at Samaru, Nigeria but were resistant to Striga at both locations in Mali. Based on low Striga resistance and high grain yield, lines MALISOR 84-1, SAMSORG 41, 97-SB-F5DT-64, 97-SB-F5DT-65, CMDT 39 and SAMSORT 14 have been nominated for wider evaluation across more West African countries. 相似文献
7.
JI Priego AG Lucas-Cuevas I Aparicio JV Giménez JM Cortell-Tormo P Pérez-Soriano 《Biology of sport / Institute of Sport》2015,32(3):219-223
The use of graduated compression stockings (GCS) in sport has been increasing in the last years due to their potential positive effects for athletes. However, there is little evidence to support whether these types of garments actually improve cardiorespiratory performance. The aim of this study was to examine the cardiorespiratory responses of GCS during running after three weeks of regular use. Twenty recreational runners performed three tests on different days: test 1) – a 5-min maximal effort run in order to determine the participants’ maximal aerobic speed; and tests 2) and 3) – a fatigue running test of 30 minutes at 80% of their maximal aerobic speed with either GCS or PLACEBO stockings at random. Cardiorespiratory parameters (minute ventilation, heart rate, relative oxygen consumption, relative carbon dioxide production, ventilatory equivalents for oxygen and carbon dioxide, and oxygen pulse) were measured. Before each test in the laboratory, the participants trained with the randomly assigned stockings (GCS or PLACEBO) for three weeks. No significant differences between GCS and PLACEBO were found in any of the cardiorespiratory parameters. In conclusion, the present study provides evidence that running with GCS for three weeks does not influence cardiorespiratory parameters in recreational runners. 相似文献
8.
Thomas GH; Newbern EC; Korte CC; Bales MA; Muse SV; Clark AG; Kiehart DP 《Molecular biology and evolution》1997,14(12):1285-1295
Many structural, signaling, and adhesion molecules contain tandemly
repeated amino acid motifs. The alpha-actinin/spectrin/dystrophin
superfamily of F-actin-crosslinking proteins contains an array of triple
alpha-helical motifs (spectrin repeats). We present here the complete
sequence of the novel beta-spectrin isoform beta(Heavy)- spectrin (beta H).
The sequence of beta H supports the origin of alpha- and beta-spectrins
from a common ancestor, and we present a novel model for the origin of the
spectrins from a homodimeric actin-crosslinking precursor. The pattern of
similarity between the spectrin repeat units indicates that they have
evolved by a series of nested, nonuniform duplications. Furthermore, the
spectrins and dystrophins clearly have common ancestry, yet the repeat unit
is of a different length in each family. Together, these observations
suggest a dynamic period of increase in repeat number accompanied by
homogenization within each array by concerted evolution. However, today,
there is greater similarity of homologous repeats between species than
there is across repeats within species, suggesting that concerted evolution
ceased some time before the arthropod/vertebrate split. We propose a
two-phase model for the evolution of the spectrin repeat arrays in which an
initial phase of concerted evolution is subsequently retarded as each new
protein becomes constrained to a specific length and the repeats diverge at
the DNA level. This evolutionary model has general applicability to the
origins of the many other proteins that have tandemly repeated motifs.
相似文献
9.
Vinpocetine prevents ischemic cell damage in rat hippocampus 总被引:3,自引:0,他引:3
D Sauer R Rischke T Beck C Rossberg H D Mennel G W Bielenberg J Krieglstein 《Life sciences》1988,43(21):1733-1739
The effects of vinpocetine on hippocampal cell damage and local cerebral blood flow (LCBF) were measured in a rat model of forebrain ischemia (2-vessel occlusion and hypotension). Duration of ischemia was 10 min. LCBF was determined after 2 min of recirculation using the 14C-iodoantipyrine technique. Hippocampal cell loss was quantified histologically 7 days post-ischemia. Intraperitoneal application of vinpocetine (10 mg/kg) 15 min prior to ischemia significantly reduced neuronal cell loss in hippocampal CA 1 sector from 60% to 28%. The drug led to a marked increase in blood flow in cortical areas, whereas LCBF remained unchanged in hippocampus and all other structures measured. It is suggested that the protective effect of vinpocetine does not depend on increased postischemic blood flow. 相似文献
10.
Food webs represent trophic (feeding) interactions in ecosystems. Since the late 1970s, it has been recognized that food-webs
have a surprisingly close relationship to interval graphs. One interpretation of food-web intervality is that trophic niche
space is low-dimensional, meaning that the trophic character of a species can be expressed by a single or at most a few quantitative
traits. In a companion paper we demonstrated, by simulating a minimal food-web model, that food webs are also expected to
be interval when niche-space is high-dimensional. Here we characterize the fundamental mechanisms underlying this phenomenon
by proving a set of rigorous conditions for food-web intervality in high-dimensional niche spaces. Our results apply to a
large class of food-web models, including the special case previously studied numerically. 相似文献