全文获取类型
收费全文 | 1318篇 |
免费 | 134篇 |
国内免费 | 217篇 |
出版年
2024年 | 17篇 |
2023年 | 60篇 |
2022年 | 62篇 |
2021年 | 49篇 |
2020年 | 59篇 |
2019年 | 71篇 |
2018年 | 59篇 |
2017年 | 68篇 |
2016年 | 85篇 |
2015年 | 58篇 |
2014年 | 70篇 |
2013年 | 67篇 |
2012年 | 46篇 |
2011年 | 62篇 |
2010年 | 31篇 |
2009年 | 106篇 |
2008年 | 72篇 |
2007年 | 89篇 |
2006年 | 79篇 |
2005年 | 53篇 |
2004年 | 43篇 |
2003年 | 43篇 |
2002年 | 44篇 |
2001年 | 30篇 |
2000年 | 23篇 |
1999年 | 27篇 |
1998年 | 25篇 |
1997年 | 17篇 |
1996年 | 15篇 |
1995年 | 15篇 |
1994年 | 14篇 |
1993年 | 4篇 |
1992年 | 11篇 |
1991年 | 9篇 |
1990年 | 6篇 |
1989年 | 11篇 |
1988年 | 13篇 |
1987年 | 4篇 |
1986年 | 13篇 |
1985年 | 11篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1973年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有1669条查询结果,搜索用时 15 毫秒
101.
Evelyn?HabitEmail author Mark?Belk Pedro?Victoriano Edilia?Jaque 《Biodiversity and Conservation》2007,16(11):3179-3191
River environments are characterized by extreme spatial and temporal variation in the physical environment. The relationship
of fish assemblages to environmental variation is poorly understood in many systems. In Chile zonation patterns of fish assemblages
have been documented in several Andean river drainages. Coastal river drainages are comparatively small, but inordinately
important because of their highly endemic flora and fauna and their proximity to major human populations. For conservation
purposes it is important to understand what environmental factors affect assemblage structure of fishes especially in the
comparatively high diversity coastal drainages. We studied patterns of fish distribution and abundance in three rivers of
the coastal, Andalien drainage near Concepción, Chile. We used multi-dimensional scaling analyses to compare patterns among
zones (rithron, transition and potamon) and high and low flow seasons. Species assemblages differed by zone, but not with
season. Assemblages consisted of nested subsets of species characterized by their range of distribution among zones. One species
group was composed of widespread species that occurred in all three zones, another species group consisted of species found
only in transitional and potamal zones, and a final group was comprised of species found only in the potamal zone. The potamal
zone contained the most diverse and abundant fish assemblage. Fish assemblages were related to both water quality and habitat
structure variables. This study suggests that the key to conserving the diversity of native fish communities in coastal Chilean
rivers is in the conservation of potamal regions. Unfortunately, most protected areas in Chile are in the depauperate headwaters
of drainages. Protection of only headwaters is clearly inadequate and will not contribute to the conservation of this unique
freshwater fish fauna. 相似文献
102.
Richard S. Nemeth Jeremiah Blondeau Steve Herzlieb Elizabeth Kadison 《Environmental Biology of Fishes》2007,78(4):365-381
This study compared the spatial and temporal patterns of red hind, Epinephelus guttatus, movement and migration from annual spawning aggregations on St Thomas (STT) and St Croix (STX), United States Virgin Islands.
Around STT E. guttatus migrated 6–33 km from a functional spawning migration area of 500 km2 and around STX E. guttatus migrated 5–18 km from an area of 90 km2. Similarities between sites were found in regards to timing of movement, temporal and spatial changes in sex ratios, annual
and lunar predictability and were synchronized with environmental cues. E. guttatus spawning aggregations in the Virgin Islands occur between the winter solstice (i.e., after December 20) and about February
20 of any year and show a distinctive peak 20–40 days after the winter solstice. Spawning typically occurred during periods
of declining seawater temperature and slacking currents within a temperature range of 26–27.5°C and current speed of 2.5–3.5 cm s−1. Males arrived early to spawning sites and stayed longer than females. These gender-based behavioral patterns are important
to E. guttatus reproductive dynamics and must be factored into future studies and the design of fisheries regulations to ensure sustainability
of spawning aggregation sites. The predictability of E. guttatus spawning aggregations relative to the winter solstice will be extremely beneficial for defining the temporal and spatial
aspects of area closures. The consistency and synchrony of movement and migration will improve both the efficiency of planning
research and monitoring programs and directing enforcement activities during critical time periods. Applying this knowledge
strategically will maximize the limited resources available for research and enforcement and lead to greater protection of
spawning aggregations. 相似文献
103.
The Mexican Government decreed Chinchorro Bank reef as a Biosphere Reserve in 1996. The aim of this study was to evaluate
the spatial and size-frequency distribution of Acropora spp. in order to provide further knowledge and tools to enhance management. A field survey was conducted, within six regions,
to locate and measure Acropora patches in the reef lagoon. Density, colony size and living tissue cover of Acropora colonies were evaluated using the line-intercept transect technique, combining direct observations and video transects. The
results showed that Acropora spp. was preferentially distributed in the southern regions; where cover and density were high. Based on these results and
considering that Acropora spp. produces landscape heterogeneity, which in turn generates shelter for other species, including some of considerable
economic importance, then at least the South East region should be considered as a key area for Acropora species conservation, and should be included in the Chinchorro Bank management plan. 相似文献
104.
Coral reef marine protected areas (MPA) are widely distributed around the globe for social and ecological reasons. Relatively
few of these MPAs are well managed. This review examines the governance of coral reef MPAs and the means to improve coral
reef MPA management. It highlights common governance challenges, such as confused goals, conflict, and unrealistic attempts
to scale up beyond institutional capacity. Recommendations, based on field experience and empirical evidence from around the
world, are made for best practices at various stages of MPA implementation.
相似文献
A. T. WhiteEmail: |
105.
Zonobiomes, zonoecotones and azonal vegetation along the Pacific coast of North America 总被引:1,自引:1,他引:0
In this study of the Pacific coast of North America, from Baja California to Alaska, we evaluated the hypothesis that the
floristic composition of azonal vegetation determines areas and distribution limits similar to those of the corresponding
zonobiomes (ZB), and does so in response to the same macroclimatic changes occurring on the continental scale. To this end,
686 vascular plants of the different habitats found in 279 sites along this coastal strip were recorded. Using an objective
classification system (Average Linkage Clustering) and factorial analysis, floristic data acquired in fieldwork were classified
into groups, which were in turn related to regional macroclimates. Our main finding was that the azonal coastal vegetation
follows a distribution model that is closely linked to the corresponding macroclimate. The four ZB of the northern Pacific
coast show a flora and azonal vegetation characteristic to each zonobiome; the latitudinal limits of the azonal vegetation
practically coinciding with those already established for the zonal vegetation. The Boreal and Temperate ZB show high percentages
of broadly distributed elements. The floristically richest zonobiome in terms of endemic taxa is the Mediterranean zonobiome,
whereas the flora of Baja California is characterized by a high number of taxa related to Neotropical flora, especially to
those showing links with South America. Data on the geographical distribution and habitats of the 247 most significant coastal
species are also provided. 相似文献
106.
《Systematic and applied microbiology》2022,45(1):126280
Chamaecrista mimosoides is an annual herb legume widely distributed in tropical and subtropical Asia and Africa. It may have primitive and independently-evolved root nodule types but its rhizobia have not been systematically studied. Therefore, in order to learn the diversity and species affinity of its rhizobia, root nodules were sampled from C. mimosoides plants growing in seven geographical sites along the coast line of Shandong Peninsula, China. A total of 422 rhizobial isolates were obtained from nodules, and they were classified into 28 recA haplotypes. By using multilocus sequence analysis of the concatenated housekeeping genes dnaK, glnII, gyrB, recA and rpoB, the representative strains for these haplotypes were designated as eight defined and five candidate novel genospecies in the genus Bradyrhizobium. Bradyrhizobium elkanii and Bradyrhizobium ferriligni were predominant and universally distributed. The symbiotic genes nodC and nifH of the representative strains showed very similar topology in their phylogenetic trees indicating their co-evolution history. All the representative strains formed effective root nodules in nodulation tests. The correlation between genospecies and soil characteristics analyzed by CANOCO software indicated that available potassium (AK), organic carbon (OC) and available nitrogen (AN) in the soil samples were the main factors affecting the distribution of the symbionts involved in this current study. The study is the first systematic survey of Chamaecrista mimosoides-nodulating rhizobia, and it showed that Chamaecrista spp. were nodulated by bradyrhizobia in natural environments. In addition, the host spectrum of the corresponding rhizobial species was extended, and the study provided novel information on the biodiversity and biogeography of rhizobia. 相似文献
107.
《Current biology : CB》2022,32(13):2810-2820.e5
108.
T. M. Brooks A. Cuttelod D. P. Faith J. Garcia-Moreno P. Langhammer S. Pérez-Espona 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2015,370(1662)
‘Key biodiversity areas'' are defined as sites contributing significantly to the global persistence of biodiversity. The identification of these sites builds from existing approaches based on measures of species and ecosystem diversity and process. Here, we therefore build from the work of Sgró et al. (2011 Evol. Appl.
4, 326–337. (doi:10.1111/j.1752-4571.2010.00157.x)) to extend a framework for how components of genetic diversity might be considered in the identification of key biodiversity areas. We make three recommendations to inform the ongoing process of consolidating a key biodiversity areas standard: (i) thresholds for the threatened species criterion currently consider a site''s share of a threatened species'' population; expand these to include the proportion of the species'' genetic diversity unique to a site; (ii) expand criterion for ‘threatened species'' to consider ‘threatened taxa’ and (iii) expand the centre of endemism criterion to identify as key biodiversity areas those sites holding a threshold proportion of the compositional or phylogenetic diversity of species (within a taxonomic group) whose restricted ranges collectively define a centre of endemism. We also recommend consideration of occurrence of EDGE species (i.e. threatened phylogenetic diversity) in key biodiversity areas to prioritize species-specific conservation actions among sites. 相似文献
109.
Piero Visconti Michel Bakkenes Robert J. Smith Lucas Joppa Rachel E. Sykes 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2015,370(1681)
Several global strategies for protected area (PA) expansion have been proposed to achieve the Convention on Biological Diversity''s Aichi target 11 as a means to stem biodiversity loss, as required by the Aichi target 12. However, habitat loss outside PAs will continue to affect habitats and species, and PAs may displace human activities into areas that might be even more important for species persistence. Here we measure the expected contribution of PA expansion strategies to Aichi target 12 by estimating the extent of suitable habitat available for all terrestrial mammals, with and without additional protection (the latter giving the counterfactual outcome), under different socio-economic scenarios and consequent land-use change to 2020. We found that expanding PAs to achieve representation targets for ecoregions under a Business-as-usual socio-economic scenario will result in a worse prognosis than doing nothing for more than 50% of the world''s terrestrial mammals. By contrast, targeting protection towards threatened species can increase the suitable habitat available to over 60% of terrestrial mammals. Even in the absence of additional protection, an alternative socio-economic scenario, adopting progressive changes in human consumption, leads to positive outcomes for mammals globally and to the largest improvements for wide-ranging species. 相似文献
110.
First record of a spawning aggregation for the tropical eastern Pacific endemic grouper Mycteroperca olfax in the Galapagos Marine Reserve
下载免费PDF全文
![点击此处可从《Journal of fish biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
This study provides direct and indirect evidence of temporally and spatially consistent spawning aggregations for the grouper Mycteroperca olfax. Recently reported declines in population numbers, probably related to the direct targeting of aggregations by artisanal fishermen, highlight the urgent need for species‐specific management actions in the Galapagos Marine Reserve, such as minimum and maximum landing sizes, and the importance of protecting key aggregation sites with the declaration of no‐take areas and the establishment of total fishing bans during the reproductive season. 相似文献