全文获取类型
收费全文 | 562篇 |
免费 | 63篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 12篇 |
2020年 | 10篇 |
2019年 | 16篇 |
2018年 | 16篇 |
2017年 | 19篇 |
2016年 | 15篇 |
2015年 | 32篇 |
2014年 | 25篇 |
2013年 | 40篇 |
2012年 | 46篇 |
2011年 | 23篇 |
2010年 | 27篇 |
2009年 | 28篇 |
2008年 | 22篇 |
2007年 | 32篇 |
2006年 | 22篇 |
2005年 | 20篇 |
2004年 | 24篇 |
2003年 | 16篇 |
2002年 | 27篇 |
2001年 | 13篇 |
2000年 | 21篇 |
1999年 | 10篇 |
1998年 | 7篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1995年 | 7篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1990年 | 10篇 |
1989年 | 3篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1971年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有625条查询结果,搜索用时 31 毫秒
111.
Ramón Pérez Gil Salcido Inés Arroyo Quiroz Roberto Romero Ramírez 《Biodiversity and Conservation》2009,18(5):1421-1434
Documenting financial resources in biodiversity conservation is a key aspect worldwide in order to set priorities and use
effectively the limited resources available. In Mexico, a megadiverse country, studies on financial resources invested in
biodiversity conservation are scarce and do not address funding for conservation comprehensively. Using recent data from several
sources and applying criteria based on the national priorities for conservation, we compiled, systematized and analyzed data
at a national scale on financing sources, financial resources and conservation organizations and their projects. The information
obtained is presented in various ways and part of it (case study) is already an information system that can be continuously
up-dated. Some of the results show the following: a steady diversification of mechanisms and methods for raising funds for
conservation; an increase in governmental budgets; the acknowledgment by the private sector of the importance of biodiversity
conservation; a greater technical capacity in people and organizations working in conservation; a greater accessibility of
financial resources to support and maintain conservation projects; yet a short term vision in conservation projects; among
other. Although the results obtained through this study are a first approach, they can now be used as a baseline to continue
gathering and analyzing information on conservation financing in Mexico. 相似文献
112.
113.
Ra��l Garc��a Jose M. Rodr��guez-Pe?a Clara Bermejo C��sar Nombela Javier Arroyo 《The Journal of biological chemistry》2009,284(16):10901-10911
114.
115.
We report 13 polymorphic nuclear microsatellite loci for Neochamaelea pulverulenta (Cneoraceae) using an enriched-library approach. Although this plant species is tetraploid, expected patterns for tetrasomic segregation were completely absent, and all loci analysed showed a diploid pattern of inheritance. We detected a total of 102 alleles in 57 individuals genotyped (mean number of alleles per locus was 7.85). The values of observed and expected heterozygosities ranged from 0.193 to 0.737 and 0.425 to 0.812 respectively. Disomic segregation, levels of polymorphism and the exclusionary power of the developed markers render them readily applicable for parentage assignment of dispersed seeds, and for analyses of spatial genetic structure and population connectivity. 相似文献
116.
Kasper Johansen Lara A. Arroyo John Armston Stuart Phinn Christian Witte 《Ecological Indicators》2010,10(4):796-807
Mapping, monitoring and managing the environmental condition of riparian zones are major focus areas for local and state governments in Australia. New remotely sensed data techniques that can provide the required mapping accuracies, complete spatial coverage and processing and mapping transferability are currently being developed for use over large spatial extents. The research objective was to develop and apply an approach for mapping riparian condition indicators using object-based image analysis of airborne Light Detection and Ranging (LiDAR) data. The indicators assessed were: streambed width; riparian zone width; plant projective cover (PPC); longitudinal continuity; coverage of large trees; vegetation overhang; and stream bank stability. LiDAR data were captured on 15 July 2007 for two 5 km stretches along Mimosa Creek in Central Queensland, Australia. Field measurements of riparian vegetation structural and landform parameters were obtained between 28 May and 5 June 2007. Object-based approaches were developed for mapping each riparian condition indicator from the LiDAR data. The validation and empirical modelling results showed that the object-based approach could be used to accurately map the riparian condition indicators (R2 = 0.99 for streambed width, R2 = 0.82 for riparian zone width, R2 = 0.89 for PPC, R2 = 0.40 for bank stability). These research findings will be used in a 26,000 km mapping project assessing riparian vegetation and physical form indicators from LiDAR data in Victoria, Australia. 相似文献
117.
Fiona Blanco-Kelly Fuencisla Matesanz Antonio Alcina María Teruel Lina M. Díaz-Gallo María Gómez-García Miguel A. López-Nevot Luis Rodrigo Antonio Nieto Carlos Carde?a Guillermo Alcain Manuel Díaz-Rubio Emilio G. de la Concha Oscar Fernandez Rafael Arroyo Javier Martín Elena Urcelay 《PloS one》2010,5(7)
Background
A functional polymorphism located at −1 from the start codon of the CD40 gene, rs1883832, was previously reported to disrupt a Kozak sequence essential for translation. It has been consistently associated with Graves'' disease risk in populations of different ethnicity and genetic proxies of this variant evaluated in genome-wide association studies have shown evidence of an effect in rheumatoid arthritis and multiple sclerosis (MS) susceptibility. However, the protective allele associated with Graves'' disease or rheumatoid arthritis has shown a risk role in MS, an effect that we aimed to replicate in the present work. We hypothesized that this functional polymorphism might also show an association with other complex autoimmune condition such as inflammatory bowel disease, given the CD40 overexpression previously observed in Crohn''s disease (CD) lesions.Methodology
Genotyping of rs1883832C>T was performed in 1564 MS, 1102 CD and 969 ulcerative colitis (UC) Spanish patients and in 2948 ethnically matched controls by TaqMan chemistry.Principal Findings
The observed effect of the minor allele rs1883832T was replicated in our independent Spanish MS cohort [p = 0.025; OR (95% CI) = 1.12 (1.01–1.23)]. The frequency of the minor allele was also significantly higher in CD patients than in controls [p = 0.002; OR (95% CI) = 1.19 (1.06–1.33)]. This increased predisposition was not detected in UC patients [p = 0.5; OR (95% CI) = 1.04 (0.93–1.17)].Conclusion
The impact of CD40 rs1883832 on MS and CD risk points to a common signaling shared by these autoimmune conditions. 相似文献118.
The genus Triptilion is endemic to central Chile, the Mendoza Province and western Patagonia in Argentina. It is currently composed of seven species: T. achilleae, T. benaventii, T. berteroi, T. capillatum, T. cordifolium, T. gibbosum, and T. spinosum. The main objectives of this paper were to determine the phylogenetic relationships of species of Triptilion. We also traced the evolution of annual and perennial life-forms. Historically a close relationship has been described between genera Triptilion and Nassauvia. Phylogenetic analysis of the genus Triptilion and more closely related genera was undertaken using two nuclear (ITS, ETS) and two chloroplast (trnL-F, rpl32-trnL) markers. The topology of the Bayesian inference tree shows that the genus Triptilion is paraphyletic, because Nassauvia lagascae, the only representative of Nassauvia section Caloptilium grouped with T. achilleae, Clade I. The other species of Triptilion form two clades: Clade II composed of T. cordifolium and T. gibbosum and Clade III that includes T. benaventii, T. berteroi, T. capillatum, and T. spinosum. The genus Triptilion originated and diverged during the Miocene. The results of the life history reconstructions indicate that the common ancestor of Triptilion and Nassauvia was perennial. The annual habit appears to be derived in Triptilion. The life-form of the common ancestor of Triptilion was ambiguous; it may have been annual or perennial. 相似文献
119.
120.
Whether human disturbance can lead to directional selection and phenotypic change in behaviour in species with limited behavioural plasticity is poorly understood in wild animal populations. Using a 19‐year study on Montagu′s harrier, we report a long‐term increase in boldness towards humans during nest visits. The probability of females fleeing or being passive during nest visits decreased, while defence intensity steadily increased over the study period. These behavioural responses towards humans were significantly repeatable. The phenotypic composition of the breeding population changed throughout the study period (4–5 harrier generations), with a gradual disappearance of shy individuals, leading to a greater proportion of bolder ones and a more behaviourally homogeneous population. We further show that nest visit frequency increased nest failure probability and reduced productivity of shy females, but not of bold ones. Long‐term research or conservation programmes needing nest visits can therefore lead to subtle but relevant population compositional changes that require further attention. 相似文献