全文获取类型
收费全文 | 217篇 |
免费 | 12篇 |
国内免费 | 4篇 |
专业分类
233篇 |
出版年
2023年 | 3篇 |
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 4篇 |
2019年 | 4篇 |
2018年 | 8篇 |
2017年 | 9篇 |
2016年 | 3篇 |
2015年 | 3篇 |
2014年 | 8篇 |
2013年 | 16篇 |
2012年 | 8篇 |
2011年 | 9篇 |
2010年 | 5篇 |
2009年 | 9篇 |
2008年 | 15篇 |
2007年 | 10篇 |
2006年 | 17篇 |
2005年 | 9篇 |
2004年 | 11篇 |
2003年 | 8篇 |
2002年 | 6篇 |
2001年 | 11篇 |
2000年 | 5篇 |
1999年 | 6篇 |
1998年 | 7篇 |
1997年 | 5篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1986年 | 1篇 |
1985年 | 6篇 |
1984年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有233条查询结果,搜索用时 15 毫秒
31.
Males of the giant water bug Appasus (= Diplonychus) japonicus Vuillefroy (Belostomatidae: Heteroptera) carry egg masses on their back, but little is known about the relationship between seasonal abundance and breeding ecology of the species. In the present study, therefore, a field survey based on a mark-and-recapture census was carried out at three survey points within a rice paddy area (0.3 km2 ) where A. japonicus forms a meta-population in northern Okayama, Japan. We investigated the body size, seasonal abundance, dispersion, egg mass size (number of eggs within one egg mass), number of egg masses and the total eggs carried on the back of each male as fundamental parameters of the population and breeding. Significant differences in egg mass size, number of egg masses, and total number of eggs that males carried was found among the survey points. The present results suggested the possibility that the differences in breeding parameters of A. japonicus were influenced by differences in environmental factors among the microhabitats. These results are discussed in conjunction with previous reports on seasonal abundance and breeding systems in Belostomatidae bugs. 相似文献
32.
33.
Seasonal and interannual variation of subtidal fish assemblages in Wakasa Bay with reference to the warming trend in the Sea of Japan 总被引:1,自引:0,他引:1
Reiji Masuda 《Environmental Biology of Fishes》2008,82(4):387-399
A bi-monthly underwater visual census was conducted in the subtidal habitat of Nagahama, Wakasa Bay, Sea of Japan, over 5 years
from January 2002 to December 2006. A total of 83 fish species and 63,328 individuals were recorded over 120 1-h visual censuses
composed of three 2 × 200 m transects. The number of both total individuals (abundance) and species (richness) were strongly
correlated with the bottom-water temperature. Species richness was greatest in summer (July–September), with 10–20 species
per 400 m2, when the sea-bottom temperature was highest (24–28°C), and lowest in winter (January–March), with 1–8 species per 400 m2, when the temperature was lowest (10–12°C). Five species, i.e., rockfish, Sebastes inermis, wrasse, Pseudolabrus sieboldi, two species of goby, Acentrogobius pflaumii and Tridentiger trigonocephalus, and pygmy filefish, Rudarius ercodes, were frequently observed and present in more than 200 of the total of 360 total transects. While the presence of most fish
species was dependent on water temperature, some species were independent of water temperature, including anchovy, Engraulis japonicus, S. inermis, wasp fish, Hypodytes rubripinnis, A. pflaumii and pufferfish, Takifugu poecilonotus. Jack mackerel, Trachurus japonicus, was the most abundant fish, being most typically seen from spring through autumn, with a total of 21,850 individuals observed
over the whole census period. Some species showed strong annual fluctuations in abundance. The interannual stability in fish
abundance and species richness was probably because the fish assemblage was composed of a sufficiently large number of species,
but with the number of each species fluctuating over time. A comparison of the present survey to one in 1970–72 revealed that
over the last 30 years southern fish species have significantly increased whereas those indigenous to northern waters have
decreased.
相似文献
Reiji MasudaEmail: |
34.
CLIFFORD G. RICE KURT J. JENKINS WAN-YING CHANG 《The Journal of wildlife management》2009,73(3):468-478
ABSTRACT Unbiased estimates of mountain goat (Oreamnos americanus) populations are key to meeting diverse harvest management and conservation objectives. We developed logistic regression models of factors influencing sightability of mountain goat groups during helicopter surveys throughout the Cascades and Olympic Ranges in western Washington during summers, 2004–2007. We conducted 205 trials of the ability of aerial survey crews to detect groups of mountain goats whose presence was known based on simultaneous direct observation from the ground (n = 84), Global Positioning System (GPS) telemetry (n = 115), or both (n = 6). Aerial survey crews detected 77% and 79% of all groups known to be present based on ground observers and GPS collars, respectively. The best models indicated that sightability of mountain goat groups was a function of the number of mountain goats in a group, presence of terrain obstruction, and extent of overstory vegetation. Aerial counts of mountain goats within groups did not differ greatly from known group sizes, indicating that under-counting bias within detected groups of mountain goats was small. We applied Horvitz-Thompson-like sightability adjustments to 1,139 groups of mountain goats observed in the Cascade and Olympic ranges, Washington, USA, from 2004 to 2007. Estimated mean sightability of individual animals was 85% but ranged 0.75–0.91 in areas with low and high sightability, respectively. Simulations of mountain goat surveys indicated that precision of population estimates adjusted for sightability biases increased with population size and number of replicate surveys, providing general guidance for the design of future surveys. Because survey conditions, group sizes, and habitat occupied by goats vary among surveys, we recommend using sightability correction methods to decrease bias in population estimates from aerial surveys of mountain goats. 相似文献
35.
Port Stephens, a large natural harbour on the central New South Wales (NSW) coast, provides ideal oceanographic and benthic conditions for the growth of marine algae and seagrasses, and this promotes a suite of herbivorous heterobranch sea slugs such as sea hares and sap-sucking sea slugs. In this article we document both historic and recent observations of sea hares (family Aplysiidae) from Port Stephens with the intention of recording species diversity. The western South Pacific region has the richest aplysiid fauna in the world, with 16 species now recorded in Port Stephens. This location is the most taxonomically diverse for this family in Australia. Despite this hotspot of aplysiid diversity, the taxonomy and nomenclature of 12 species is uncertain, a fact highlighted by a series of nomenclatural notes included in this article. We herein report the first observation of Petalifera sp. in Australian waters. Dolabrifera jacksoniensis Pilsbry, 1896 is newly synonymised with D. brazieri G.B. Sowerby II, 1870. Recent reports of southern range extensions for other heterobranch sea slugs, both in Port Stephens and elsewhere in NSW, highlight the importance of recording the existing aplysiid diversity in the port. Thus, any future alteration to species composition and range shifts driven by climate change may be detected. 相似文献
36.
- 1 Population density alone is unlikely to be a good predictor of the impacts of deer on their environment. The assessment of management requirements should therefore be based on assessment of deer impacts, alongside estimates of density.
- 2 Both density and impacts need to be monitored at a landscape scale, and there is a need to develop appropriate methodologies that allow managers to consider the current and likely future impact of deer.
- 3 The relevant scale for assessment (and management) varies both with deer species and context of impact, but should always encompass at least the estimated biological range of the population of deer present in an area. Some impacts (e.g. deer–vehicle collisions, and risks of disease transmission) may need to be assessed at a wider regional level.
- 4 In this review we consider various approaches available for assessing: absolute or relative animal abundance; impacts of ungulates on agriculture, forestry, amenity woodlands and other conservation sites; impacts on public safety (e.g. through road traffic accidents) and on humans or livestock through potential spread of disease.
- 5 In each case the advantages and disadvantages of a variety of methods are considered, before recommendations are made for methodologies which are sufficiently accurate, sufficiently robust and sufficiently practical to be favoured in a management context.
- 6 To address impacts at the landscape scale requires management policies that integrate information on both positive and negative impacts of deer in order to ensure appropriate and holistic management. We present a decision‐support framework suitable for use within the UK, using inputs from a variety of possible impact types to assist managers and forewarn of situations where current management may need to be modified.
37.
We review the four major contemporary methods for estimating density of group-living animals from line-transect sampling: perpendicular modelling of group centers, perpendicular modelling of center of measurable individuals, strip transects and animal-observer distance. The efficacy of each method is evaluated to produce a simple selection guide. We review the literature and use field data from the Udzungwa Mountains, Tanzania. The review is relevant to all group-living animals; however, examples are drawn from the primates. Perpendicular methods have better mathematical justification than non-perpendicular methods. For perpendicular methods using detection function models, it is preferable to measure group location using center of measurable individuals, as group centers are hard to estimate. The assumptions of detection function models are often broken in poor visibility habitats or with unhabituated animals. Alternatively strip transects may be used where there are reliable data on group spread and/or visibility. Strip transects are also the most practical, along with the animal-observer method; however, the latter lacks mathematical justification. We conclude that there are arguments for continued use of all four methods. In certain situations the use of raw encounter rates may also be considered. The appropriate method is determined by minimizing bias and considering time, resources and field conditions. 相似文献
38.
We studied genetic drift of mitochondrial DNA (mtDNA) haplotype frequencies in a natural population of red drum (Sciaenops ocellatus) from the northern Gulf of Mexico (Gulf). The amount of genetic drift observed across temporally adjacent year classes (1986–89) was used to estimate variance effective (female) population size (Nef). Nef was estimated to be 14 308 and the ratio of female effective size to adult female census size was approximately 0.004, which is among the lowest value reported for vertebrate animals. Low effective size relative to census size among red drum in the northern Gulf may result from yearly fluctuations in the number of breeding females, high variance in female reproductive success, or both. Despite low genetic effective size relative to census size, the genetic effective population size of red drum in the northern Gulf appears sufficiently large to preclude potentially deleterious effects of inbreeding. 相似文献
39.
Caroline E. G. Tutin Richard J. Parnell Lee J. T. White Michel Fernandez 《International journal of primatology》1995,16(2):53-76
We analyzed data from 373 fresh nest-sites (containing 2435 nests) of lowland gorillas (Gorilla g. gorilla)during a 4-year period in the Lopé Reserve, Gabon, to determine whether the observed variability in nest building was due
to environmental influences. We recognized and defined seven types of nest in terms of the degree of construction and the
raw materials used. Overall, nests built on the ground from herbaceous plants are the most common type (40%), followed by
tree nests (35%). Frequencies of the different nest-types vary significantly between eight habitat-types. In habitat-types
with high densities of understory herbs, ground nests predominated, but when herbs were rare, the majority of nests were in
trees. A general preference for sleeping in herbaceous ground nests is indicated since trees are abundant in all habitat-types,
except savanna. The frequency of nesting in trees shows a significant positive correlation with rainfall, but effects of climate
are confounded by seasonal variation in use of different habitat-types. When elephants were attracted to the same localized
food sources as gorillas, many tree nests were built even when herbs were available. We conclude that different nest-types
reflect a variety of solutions to maximize comfort, depending on available raw materials and the probability of rainfall or
disturbance by elephants or both factors. Nests are a powerful tool for population censuses and demographic studies of great
apes, but problems exist in interpreting data on lowland gorilla nests. Results from this analysis show that only a third
of nest-sites accurately reflects group size (of weaned individuals) and that 26% of all gorilla nest-sites could be mistaken
for those of chimpanzees, as all nests, or all those visible from a transect, were in trees. Gorilla nests at Lopé were nonrandomly
distributed with respect to habitat-types, and nest construction varied seasonally, thereby introducing sources of bias to
transect nest counts. We discuss these problems and ones related to assessing the decay rate of nest-sites and make recommendations
relevant to census work. 相似文献
40.