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51.
We provide the first direct evidence that Steller sea lions will prey on harbor seals. Direct observations of predation on marine mammals at sea are rare, but when observed rates of predation are extrapolated, predation mortality may be found to be significant. From 1992 to 2002, harbor seals in Glacier Bay declined steeply, from 6,200 to 2,500 (∼65%). After documenting that Steller sea lions were preying on seals in Glacier Bay, we investigated increased predation by sea lions as a potential explanation for the large decline. In five independent data sets spanning 21–25 yr and including 14,308 d of observations, 13 predation events were recorded. We conducted a fine-scale analysis for an intensively studied haul-out (Spider Island) and a broader analysis of all of Glacier Bay. At Spider Island, estimated predation by sea lions increased and could account for the entirety of annual pup production in 5 of 8 yr since 1995. The predation rate, however, was not proportional to the number of predators. Predation by Steller sea lions is a new source of mortality that contributed to the seal declines; however, life history modeling indicates that it is unlikely that sea lion predation is the sole factor responsible for the large declines. 相似文献
52.
Wadley L 《Journal of human evolution》2007,52(6):681-689
Sibudu Cave in KwaZulu-Natal, South Africa, has a long Middle Stone Age (MSA) sequence with good organic preservation. The uppermost MSA sequence includes industries attributed to the final and late MSA and the Howiesons Poort. Below the Howiesons Poort are two layers containing some thin, bifacial lanceolate points, mostly in the form of distal and proximal fragments. These double-pointed foliates are the fossile directeur of the Still Bay Industry, and importantly, this Sibudu industry provides confirmation that the Still Bay predates the Howiesons Poort Industry. Technologically, the points from Sibudu are comparable to those from other South African sites with Still Bay occurrences (e.g., Blombos Cave and Hollow Rock Shelter). Although dating of the Sibudu Still Bay is preliminary, its age falls within the range of that at Blombos. For the past two decades, archaeologists have rejected the idea of a Still Bay Industry occurring outside of the Western Cape, but the Still Bay at Sibudu shows that this industry was, indeed, geographically widespread. 相似文献
53.
M.S. Koch S. Schopmeyer C.J. Madden 《Journal of experimental marine biology and ecology》2007,341(1):91-101
To examine the synergism of high temperature and sulfide on two dominant tropical seagrass species, a large-scale mesocosm experiment was conducted in which sulfide accumulation rates (SAR) were increased by adding labile carbon (glucose) to intact seagrass sediment cores across a range of temperatures. During the initial 10 d of the 38 d experiment, porewater SAR in cores increased 2- to 3-fold from 44 and 136 μmol L− 1 d− 1 at 28-29 °C to 80 and 308 μmol L− 1 d− 1 at 34-35 °C in Halodule wrightii and Thalassia testudinum cores, respectively. Labile C additions to the sediment resulted in SAR of 443 and 601 μmol L− 1 d− 1 at 28-29 °C and 758 to 1,557 μmol L− 1 d− 1 at 34-35 °C in H. wrightii and T. testudinum cores, respectively. Both T. testudinum and H. wrightii were highly thermal tolerant, demonstrating their tropical affinities and potential to adapt to high temperatures. While plants survived the 38 d temperature treatments, there was a clear thermal threshold above 33 °C where T. testudinum growth declined and leaf quantum efficiencies (Fv/Fm) fell below 0.7. At this threshold temperature, H. wrightii maintained shoot densities and leaf quantum efficiencies. Although H. wrightii showed a greater tolerance to high temperature, T. testudinum had a greater capacity to sustain biomass and short shoots under thermal stress with labile C enrichment, regardless of the fact that sulfide levels in the T. testudinum cores were 2 times higher than in the H. wrightii cores. Tropical seagrass tolerance to elevated temperatures, predicted in the future with global warming, should be considered in the context of the sediment-plant complex which incorporates the synergism of plant physiological responses and shifts in sulfur biogeochemistry leading to increased plant exposure to sulfides, a known toxin. 相似文献
54.
ANNE M. MECKSTROTH A. KEITH MILES SUDEEP CHANDRA 《The Journal of wildlife management》2007,71(7):2387-2392
ABSTRACT In a study of predation on ground-nesting birds at South San Francisco Bay (South Bay), California, USA, we analyzed stomach contents and stable isotopes of carbon and nitrogen to identify commonly consumed prey. We obtained the stomach contents from 206 nonnative red foxes (Vulpes vulpes regalis) collected in the South Bay area and Monterey County during 1995–2001 and from 68 feral cats (Felis silvestris) from the South Bay area during 2001–2002. We determined prey identity, biomass, and frequency, described seasonal diet trends, and derived an Index of Relative Importance. Avian species were the most frequent prey we found in the stomachs of red foxes from South Bay (61%), whereas small rodents were most frequent for red foxes from Monterey County (62%). Small rodents were the most frequent prey we found in feral cats (63%). Carbon and nitrogen isotopic signatures for foxes supported stomach content findings. However, isotope results indicated that cats received a majority of their energy from a source other than rodents and outside the natural system, which differed from the stomach content analysis. We demonstrated the utility of both stable isotope and stomach content analyses to establish a more complete understanding of predators' diets. This information aids natural resource managers in planning and evaluating future predator-removal programs and increases our understanding of the impacts of nonnative foxes and cats on native species. 相似文献
55.
Shorebird predation of horseshoe crab eggs in Delaware Bay: species contrasts and availability constraints 总被引:2,自引:0,他引:2
Gillings S Atkinson PW Bardsley SL Clark NA Love SE Robinson RA Stillman RA Weber RG 《The Journal of animal ecology》2007,76(3):503-514
1. Functional responses -- the relationship between resource intake rate and resource abundance -- are widely used in explaining predator-prey interactions yet many studies indicate that resource availability is crucial in dictating intake rates. 2. For time-stressed migrant birds refuelling at passage sites, correct decisions concerning patch use are crucial as they determine fattening rates and an individual's future survival and reproduction. Measuring availability alongside abundance is essential if spatial and temporal patterns of foraging are to be explained. 3. A suite of shorebird species stage in Delaware Bay where they consume horseshoe crab Limulus polyphemus eggs. Several factors including spawning activity and weather give rise to marked spatial and temporal variation in the abundance and availability of eggs. We undertook field experiments to determine and contrast the intake rates of shorebird species pecking for surface and probing for buried eggs. 4. Whether eggs were presented on the sand surface or buried, we demonstrate strong aggregative responses and rapid depletion (up to 80%). Depletion was greater at deeper depths when more eggs were present. No consistent give-up densities were found. Type II functional responses were found for surface eggs and buried eggs, with peck success twice as high in the former. Maximum intake rates of surface eggs were up to 83% higher than those of buried eggs. 5. Caution is needed when applying functional responses predicted on the basis of morphology. Our expectation of a positive relationship between body size and intake rate was not fully supported. The smallest species, semipalmated sandpiper, had the lowest intake rate but the largest species, red knot, achieved only the same intake rate as the mid-sized dunlin. 6. These functional responses indicate that probing is rarely more profitable than pecking. Currently, few beaches provide egg densities sufficient for efficient probing. Areas where eggs are deposited on the sand surface are critical for successful foraging and ongoing migration. This may be especially true for red knot, which have higher energetic demands owing to their larger body size yet appear to have depressed intake rates because they consume smaller prey than their body size should permit. 相似文献
56.
粤东柘林湾中肋骨条藻(Skeletonema costatum)种群生态学 总被引:2,自引:0,他引:2
于2000年5月~2004年12月对粤东大规模养殖区柘林湾的赤潮藻中肋骨条藻(Skeletonema costatum)种群的时空分布进行了长达5a的调查。结果表明,中肋骨条藻种群密度的周年变动模式基本为双峰型,平面分布没有显著的空间差异。调查期间,中肋骨条藻种群密度的站位实测值为0~1.4×10^7cells/dm^3,总均值为3.3×10^5cells/dm^3,占浮游植物总细胞数的67.1%,为调查海区第1优势种。在总共1045份样品中,有中肋骨条藻出现的样品数为1020份。其中,种群密度大于10^6cells/dm^3的样品有65份,大于10^7cells/dm。则有4份。以大于10^6cells/dm^3为中肋骨条藻的赤潮密度标准,在调查期间至少于2000年、2003年发生4次赤潮。运用灰关联理论对中肋骨条藻种群密度与13个环境因子的关系进行排序分析发现,水温、pH值和浮游动物是影响柘林湾中肋骨条藻种群时空分布的关键因子。水温还与中肋骨条藻种群密度的对数值具极显著意义的线性关系,而达到赤潮密度的样品均落在24.5~32.0℃区间,即每年的5~9月份高温季节。由于柘林湾浮游动物的年高峰期也出现在高温季节,说明浮游动物摄食压力的存在可能是柘林湾中肋骨条藻赤潮发生的重要抑制因子。2004年调查海区中肋骨条藻种群密度和在浮游植物群落中的优势度骤然降低,可能与水体营养盐结构和Fe含量的变化有关。因此,长期调查与监测对于研究海湾生态学和赤潮发生机制是极为重要的。 相似文献
57.
V. L. Filgueiras L. S. Campos H. P. Lavrado R. Frensel R. C. G. Pollery 《Polar Biology》2007,30(11):1439-1447
A 0.0625 m2 mini-box corer (MBC) was used to study the vertical distribution of macrobenthos in the shallow sublittoral zone of Admiralty
Bay, during the 2003/2004 summer, near the Brazilian Station Comandante Ferraz, and the Peruvian Station Machu Picchu. Sediment
samples were taken from 20, 30 and 60 m, and stratified for particle-size, total organic matter (TOM) and faunal composition
analysis. The most abundant taxa were Polychaeta, Oligochaeta, Amphipoda, Cumacea, Bivalvia and Gastropoda. In general, macrofauna
were concentrated in the 0–4 cm layer (64% of total organisms). Correlations between sediment characteristics and faunal densities
have not completely explained neither the aggregation of organisms at the surface sediment layers nor the differences in faunal
composition between locations at 20 m depth. Analysis of parameters such as organic carbon, heavy metals, interstitial water,
and species composition should contribute to a better understanding of the diversity patterns found in this study. 相似文献
58.
The breeding performance and population trends of Adélie penguins (Pygoscelis adeliae) was studied at Esperanza/Hope Bay, Antarctic Peninsula, by comparing an area with low levels of human disturbance (LLD)
and an area with high levels of human disturbance (HLD), close to an Argentine research station. From 1995/1996 to 2004/2005
(except for 1999/2000 and 2003/2004), the following population parameters were measured in both areas: (1) the number of breeding
pairs, (2) the number of chicks in creches and (3) the number of chicks produced by breeding pairs. Counts were made for 26
breeding groups situated in the LLD area and 63 breeding groups located in the HLD area. The number of chicks per breeding
pair was obtaobtained by following 100 marked nests in each area. All parameters were measured as described in the CCAMLR
Monitoring Program protocols. The magnitude and direction (increasing or decreasing) of the changes in breeding population
size and the number of chicks creched were similar in both areas. Overall, the number of breeding pairs decreased from 4,744
to 2,968 (37.4%) in the LLD area, and from 8,744 to 5,378 (38.6%) in the HLD area. The number of chicks fledged increased
from 3,808 to 4,065 (6.7%) in the LLD area, and decreased from 6,991 to 6,712 (4%) in the HLD area. Breeding success (chicks
fledged per marked nest) did not differ significantly between areas for most of the seasons compared. In 1996/1997, breeding
success was significantly higher in the HLD area. Our data suggest that environmental influences currently exert greater effects
than human disturbance on the penguin population at Esperanza Bay. 相似文献
59.
We have conducted a preliminary study of tidal and diurnal variations in the distribution of dominant larval and juvenile
fishes in the Chikugo River inlet (Ariake Bay, Kyushu, Japan) to determine whether selective tidal stream transport (STST)
occurs. Larval and juvenile fish were collected from the mesohaline zone of the Chikugo River inlet during spring 2002. Temperature,
salinity, depth, and current velocity were measured. Larval and juvenile abundance were compared among four tidal conditions,
flooding tide, high tide, ebbing tide, and low tide, and between day and night. A total of 12 families, 15 species, and 5,577
individuals were collected. Temperature did not vary significantly with tidal conditions whereas salinity, depth, and current
velocity varied significantly. Salinity also was correlated significantly and positively with depth. The abundance of most
of the fishes was correlated positively and significantly with salinity and depth. Lateolabrax japonicus, Trachidermus fasciatus, Acanthogobius hasta, and other gobiid larvae (Gobiidae spp.) were significantly more abundant during high tide; in contrast, Coilia nasus and Neosalanx reganius were most abundant during low tide. The abundance of most of the fishes was higher during high tides at night than during
the day, indicating the existence of STST, which may be strategically associated with ascending progress to upstream nursery
areas. 相似文献
60.
Abstract Broadscale habitat use by Eastern Curlews (Numenius madagascariensis) in their non‐breeding range in eastern Australia was assessed using low tide surveys on feeding grounds, where 60 skilled volunteers made repeated counts of the birds on intertidal flats, across 41% (9500 ha) of the intertidal habitat within Moreton Bay, Australia. We analysed 32 defined sections of intertidal flat, of roughly equal area (mostly 200–400 ha), which varied greatly in their curlew density (2–47 birds per 100 ha) and also in substrate and other environmental features. Sites with the least resistant substrates had densities three times those with the most resistant substrates. Of 10 environmental characteristics measured for each site, substrate resistance was the best predictor of curlew density (r2 = 0.45). Characteristics that were poor predictors included distance to the nearest roost, level of human disturbance and distance to urban settlement. For a finer‐scale assessment, microhabitat use and feeding behaviour were recorded during low tide within 12 intertidal flats, which varied in size (23–97 ha), substrate, topography and other features. Across all flats, curlews strongly preferred to feed relatively close (0–50 m) to the low‐water line. They fed on a variety of substrates (including sand, sandy‐mud, mud and seagrass) in broadly similar proportions to their occurrence in the habitat. There was a statistically significant preference for sand, although its magnitude was not strong. These results indicate that curlews select habitat most strongly at a between‐flat rather than within‐flat scale. 相似文献