全文获取类型
收费全文 | 9893篇 |
免费 | 6篇 |
国内免费 | 3篇 |
专业分类
安全科学 | 17篇 |
废物处理 | 777篇 |
环保管理 | 1264篇 |
综合类 | 955篇 |
基础理论 | 3176篇 |
环境理论 | 1篇 |
污染及防治 | 1774篇 |
评价与监测 | 1032篇 |
社会与环境 | 905篇 |
灾害及防治 | 1篇 |
出版年
2022年 | 3篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2019年 | 6篇 |
2018年 | 1476篇 |
2017年 | 1377篇 |
2016年 | 1200篇 |
2015年 | 131篇 |
2014年 | 19篇 |
2013年 | 19篇 |
2012年 | 470篇 |
2011年 | 1352篇 |
2010年 | 702篇 |
2009年 | 616篇 |
2008年 | 888篇 |
2007年 | 1240篇 |
2006年 | 17篇 |
2005年 | 30篇 |
2004年 | 48篇 |
2003年 | 74篇 |
2002年 | 105篇 |
2001年 | 16篇 |
2000年 | 18篇 |
1999年 | 5篇 |
1998年 | 12篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 12篇 |
1983年 | 13篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1975年 | 3篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1935年 | 2篇 |
排序方式: 共有9902条查询结果,搜索用时 221 毫秒
991.
A common explanation for hunting in groups is that doing so yields a greater per capita caloric benefit than hunting solitarily.
This is logical for social carnivores, which rely exclusively on meat for energy, but arguably not for omnivores, which obtain
calories from either plant or animal matter. The common chimpanzee, Pan troglodytes, is one of the few true omnivores that regularly hunts in groups. Studies to date have yielded conflicting data regarding
the payoffs of group hunting in chimpanzees. Here, we interpret chimpanzee hunting patterns using a new approach. In contrast
to the classical assumption that hunting with others maximizes per capita caloric intake, we propose that group hunting is
favored because it maximizes an individual’s likelihood of obtaining important micronutrients that may be found in small quantities
of meat. We describe a mathematical model demonstrating that group hunting may evolve when individuals can obtain micronutrients
more frequently by hunting in groups than by hunting solitarily, provided that group size is below a certain threshold. Twenty
five years of data from Gombe National Park, Tanzania are consistent with this prediction. We propose that our ‘meat-scrap’
hypothesis is a unifying approach that may explain group hunting by chimpanzees and other social omnivores. 相似文献
992.
Polymorphism frequently correlates with specialized labor in social insects, but extreme morphologies may compromise behavioral
flexibility and thus limit caste evolution. The ant genus Pheidole has dimorphic worker subcastes in which major workers appear limited due to their morphology to performing defensive or trophic
functions, thus providing an ideal model to investigate specialization and plasticity. We examined worker morphology, brood-care
flexibility, and subcaste ratio in 17 species of tropical twig-nesting Pheidole by quantifying nursing by major workers in natural colonies and in subcolonies lacking minors, in which we also measured
brood survival and growth. Across species, majors performed significantly less brood care than minors in intact colonies,
but increased rates of brood care 20-fold in subcolonies lacking minors. Brood nursed by majors had lower survival than brood
tended by minors, although rates of brood growth did not vary between subcastes. Significant interspecific variation in rates
of brood care by major workers did not lead to significant differences in brood growth or survival. Additionally, we did not
find a significant association between the degree of major worker morphometric specialization and rates of nursing, growth,
or survival of brood among species. Therefore, major workers showed reduced efficacy of brood care, but the degree of morphological
specialization among species did not directly compromise task plasticity. The compact nests and all-or-nothing consequences
of predation or disturbance on colony fitness may have influenced the evolution of major worker brood-care competency in twig-nesting
Pheidole.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Dedicated to Professor Edward O. Wilson on the occasion of his 80th birthday. 相似文献
993.
Marion Valeix Hervé Fritz Andrew J. Loveridge Zeke Davidson Jane E. Hunt Felix Murindagomo David W. Macdonald 《Behavioral ecology and sociobiology》2009,63(10):1483-1494
A central question in the study of predator–prey relationships is to what extent prey behaviour is determined by avoidance
of predators. Here, we test whether the long-term risk of encountering lions and the presence of lions in the vicinity influence
the behaviour of large African herbivores at waterholes through avoidance of high-risk areas, increases in group size, changes
in temporal niche or changes in the time spent in waterhole areas. In Hwange National Park, Zimbabwe, we monitored waterholes
to study the behaviour of nine herbivore species under different risks of encountering lions. We radio-collared 26 lions in
the study area which provided the opportunity to monitor whether lions were present during observation sessions and to map
longer-term seasonal landscapes of risk of encountering lions. Our results show that the preferred prey species for lions
(buffalo, kudu and giraffe) avoided risky waterholes. Group size increased as encounter risk increased for only two species
(wildebeest and zebra), but this effect was not strong. Interestingly, buffalo avoided the hours of the day which are dangerous
when the long-term and short-term risks of encountering lions were high, and all species showed avoidance of waterhole use
at night times when lions were in the vicinity. This illustrates well how prey can make temporal adjustments to avoid dangerous
periods coinciding with predator hunting. Additionally, many herbivores spent more time accessing water to drink when the
long- and short-term risks of encountering lions were high, and they showed longer potential drinking time when the long-term
risk of encountering lions was high, suggesting higher levels of vigilance. This study illustrates the diversity of behavioural
adjustments to the risk of encountering a predator and how prey respond differently to temporal variations in this risk. 相似文献
994.
In many species, the ability to evade predators is known to be periodically impaired by increased weight loads due to feeding
and reproduction. Not only may extra weight reduce escape speed, but feeding and mating can also make the prey more noticeable
to visually hunting predators. A number of butterfly species mate for hours, and if a mating couple is disturbed, one of the
butterflies is responsible for flying, whereas its partner remains still. This study investigated the ability of male Pieris napi butterflies to fly while mating, with the prediction that mate carrying impairs flight ability compared to single flying
males and that males with relatively high flight muscle ratios (FMR; male thorax mass/male + female body mass) will have better
flight performance in copula. Our results clearly show that whereas single males always take off at steep angles and fly upwards,
couples invariably have a negative take-off angle and rarely gain height. Moreover, landing height of the couples is positively
associated with higher FMR. Hence, male flight ability when in copula is positively associated with a high relative thorax
mass. Butterfly pairs may thus be at greater risk of predation as a consequence of their impaired flight ability, especially
couples with critically low FMRs (<16%). 相似文献
995.
Elva J. H. Robinson Thomas O. Richardson Ana B. Sendova-Franks Ofer Feinerman Nigel R. Franks 《Behavioral ecology and sociobiology》2009,63(5):779-636
Ant colonies are factories within fortresses (Oster and Wilson 1978). They run on resources foraged from an outside world fraught with danger. On what basis do individual ants decide to leave the safety of the nest? We investigated the relative roles of social information (returning nestmates), individual experience and physiology (lipid stores/corpulence) in predicting which ants leave the nest and when. We monitored Temnothorax albipennis workers individually using passive radio-frequency identification technology, a novel procedure as applied to ants. This method allowed the matching of individual corpulence measurements to activity patterns of large numbers of individuals over several days. Social information and physiology are both good predictors of when an ant leaves the nest. Positive feedback from social information causes bouts of activity at the colony level. When certain social information is removed from the system by preventing ants returning, physiology best predicts which ants leave the nest and when. Individual experience is strongly related to physiology. A small number of lean individuals are responsible for most external trips. An individual’s nutrient status could be a useful cue in division of labour, especially when public information from other ants is unavailable. 相似文献
996.
Although many avian eggs appear to be cryptically colored, many species also lay vibrant blue green eggs. This seemingly conspicuous
coloration has puzzled biologists since Wallace, as natural selection should favor reduced egg visibility to minimize predation
pressure. The sexual signaling hypothesis posits that blue green egg coloration serves as a signal of female quality and that
males exert post-mating sexual selection on this trait by investing more in the nests of females laying more intensely blue
green eggs. This hypothesis has received mixed support to date, and most previous studies have been conducted in cavity-nesting
species where male evaluation of his partner’s egg coloration, relative to that of other females, may be somewhat limited.
In this study, we test the sexual signaling hypothesis in colonially nesting ring-billed gulls (Larus delawarensis) where males have ample opportunity to assess their mate’s egg coloration relative to that of other females. We used correlational
data and an experimental manipulation to test four assumptions and predictions of the sexual signaling hypothesis: (1) blue
green pigmentation should be limiting to females; (2) extent of blue green egg coloration should relate to female quality;
(3) extent of blue green egg coloration should relate to offspring quality; and (4) males should provide more care to clutches
with higher blue green chroma. Our data provide little support for these predictions of the sexual signaling hypothesis in
ring-billed gulls. In light of this and other empirical data, we encourage future studies to consider additional hypotheses
for the evolution of blue green egg coloration. 相似文献
997.
Gine Roll Skjærvø Bård G. Stokke Eivin Røskaft 《Behavioral ecology and sociobiology》2009,63(8):1133-1140
The aim of this study was to test the hypothesis that parent–offspring conflict over parental investment might have led to
the rarity of dizygotic twins in humans. We explored the theoretical prediction that twins maximize their inclusive fitness
by the death of a co-twin, while mothers of twins maximize fitness by raising both twins to independence. We used life history
data (1700–1900) from two parishes in Central Norway to compare differences in inclusive fitness (measured as number of children
reared to the age of 16 years, using Hamilton's rule) between twins and mothers of twins. Our results show that twins maximize
their inclusive fitness by the death of a co-twin, while mothers of twins raise more children by rearing both twins to adulthood.
However, because twins growing up as singletons may produce higher or at least equal number of offspring than the sum of the
two twins growing up together, mothers might gain more grandchildren by allowing twins to grow up as singletons. To conclude,
both selfish twins and their mothers might benefit by the death of a co-twin, indicating that there is no parent–offspring
conflict responsible for the rareness of twins in these human populations. Finally, we discuss the results in the light of
“The Insurance Egg Hypothesis” and “The Natural Selection Hypothesis”. 相似文献
998.
Complex marine ecosystems contain multiple feedback cycles that can cause unexpected responses to perturbations. To better predict these responses, complicated models are increasingly being developed to enable the study of feedback cycles. However, the sparseness of ecological data often limits the direct empirical parameterization of all model parameters. Here we use a Bayesian inverse analysis approach to synthesize empirical data and ecological theory derived from published studies of a coral atoll's enclosed pelagic ecosystem (Takapoto Atoll, French Polynesia). We then use the estimates of flux magnitudes to parameterize probabilistic compartment models with two forms of heterotrophic consumption: (1) “bottom-up” donor-controlled heterotrophic consumption and (2) “top-down” mass-action heterotrophic consumption. We explore how the flux magnitudes affect the ecosystem's stability properties of resilience, reactivity, and resistance under both assumptions for heterotrophic consumption. The models suggest that the microbial uptake of dissolved organic carbon (DOC) regulates the long term rate of return to steady state following a temporary or pulse perturbation (resilience), and the cycling of carbon between abiotic pools and heterotrophic compartments regulates the short-term response (reactivity). In the bottom-up process model, the sensitivity of steady state masses following a sustained or press perturbation (resistance) is highest for the DOC pool following a sustained change to the microbial uptake rate of DOC. Further, a change in the microbial uptake of DOC propagates through the ecosystem and affects the steady state values of zooplankton. The analysis suggests that the food web is highly dependent on the recycling between the abiotic and biotic carbon pools, particularly as mediated by the microbial consumption of DOC, and this recycling determines how the ecosystem responds to perturbations. 相似文献
999.
Megalopae of several crab species exhibit active habitat selection when settling. These megalopae usually select structurally
complex habitats which can provide refuge and food. The portunid mud crab, Scylla serrata, is commonly found within the muddy estuaries of the Indo-West Pacific after attaining a carapace width >40 mm. Despite substantial
efforts, the recruitment mechanism of juvenile mud crabs to estuaries is not understood because their megalopae and early
stage crablets (carapace width <30 mm) are rarely found. We used laboratory experiments to determine whether megalopae and
early stage crablets are selective among three estuarine habitats which commonly occur in Queensland, Australia. These animals
were placed in arenas where they had a choice of habitats: seagrass, mud or sand, and arenas where they had no choice. Contrary
to the associations exhibited by other portunid crab megalopae, S. serrata megalopae were not selective among these estuarine habitats, suggesting that they tend not to encounter these habitats, or,
gain no advantage by selecting one over the others. The crablets, however, strongly selected seagrass, suggesting that residing
within seagrass is beneficial to the crablets and likely increases survival. This supports the model that for S. serrata, crablets and not megalopae tend to colonise estuaries, since a selective behaviour has evolved within crablets but not megalopae. 相似文献
1000.
The effects of light exposure on the photosynthetic activity of kleptoplasts were studied in the sacoglossan mollusc Elysia viridis. The photosynthetic activity of ingested chloroplasts was assessed in vivo by non-destructively measuring photophysiological
parameters using pulse amplitude modulation (PAM) fluorometry. Animals kept under starvation were exposed to two contrasting
light conditions, 30 μmol photons m−2 s−1 (low light, LL), and 140 μmol photons m−2 s−1 (high light, HL), and changes in photosynthetic activity were monitored by measuring the maximum quantum yield of photosystem
II (PSII), F
v/F
m, the minimum fluorescence, F
o, related to chlorophyll a content, and by measuring rapid light-response curves (RLC) of relative electron transport rate (rETR). RLCs were characterised
by the initial slope of the curve, αRLC, related to efficiency of light capture, and the maximum rETR level, rETRm,RLC, determined by the carbon-fixation metabolism. Starvation induced the decrease of all photophysiological parameters. However,
the retention of photosynthetic activity (number of days for F
v/F
m > 0), as well as the rate and the patterns of its decrease over time, varied markedly with light exposure. Under HL conditions,
a rapid, exponential decrease was observed for F
v/F
m, αRLC and rETRm,RLC, F
o not showing any consistent trend of variation, and retention times ranged between 6 and 15 days. These results suggested
that the retention of chloroplast functionality is limited by photoinactivation of PSII reaction center protein D1. In contrast,
under LL conditions, a slower decrease in all parameters was found, with retention times varying from 15 to 57 days. F
v/F
m, αRLC and rETRm,RLC exhibited a bi-phasic pattern composed by a long phase of slow decrease in values followed by a rapid decline, whilst F
o decayed exponentially. These results were interpreted as resulting from lower rates of D1 photoinactivation under low light
and from the gradual decrease in carbon provided by photosynthesis due to reduction of functional photosynthetic units. 相似文献