全文获取类型
收费全文 | 894篇 |
免费 | 55篇 |
国内免费 | 48篇 |
专业分类
安全科学 | 137篇 |
废物处理 | 19篇 |
环保管理 | 94篇 |
综合类 | 235篇 |
基础理论 | 396篇 |
污染及防治 | 30篇 |
评价与监测 | 30篇 |
社会与环境 | 40篇 |
灾害及防治 | 16篇 |
出版年
2023年 | 5篇 |
2022年 | 11篇 |
2021年 | 15篇 |
2020年 | 21篇 |
2019年 | 11篇 |
2018年 | 10篇 |
2017年 | 24篇 |
2016年 | 28篇 |
2015年 | 21篇 |
2014年 | 26篇 |
2013年 | 35篇 |
2012年 | 44篇 |
2011年 | 56篇 |
2010年 | 54篇 |
2009年 | 54篇 |
2008年 | 73篇 |
2007年 | 78篇 |
2006年 | 83篇 |
2005年 | 59篇 |
2004年 | 51篇 |
2003年 | 33篇 |
2002年 | 19篇 |
2001年 | 19篇 |
2000年 | 24篇 |
1999年 | 30篇 |
1998年 | 21篇 |
1997年 | 20篇 |
1996年 | 20篇 |
1995年 | 18篇 |
1994年 | 12篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1982年 | 1篇 |
1979年 | 1篇 |
1977年 | 2篇 |
1975年 | 1篇 |
排序方式: 共有997条查询结果,搜索用时 140 毫秒
401.
Nest or roost temperature (T
roost) is thought to impact reproductive fitness in many endotherms but few studies have directly tested the hypothesis that naturally
occurring variability in nest or roost microclimate is large enough to affect reproductive success. We conducted a field experiment
to test whether roost selection by cavity-dwelling, reproductive female big brown bats (Eptesicus fuscus) is more strongly influenced by roost microclimate or a physical characteristic of roosts that facilitates social thermoregulation
(i.e., cavity volume). We quantified spatial variability in T
roost within different-sized, unoccupied cavities and also recorded T
roost in occupied vs unoccupied roost trees. We used equations relating energy use and ambient temperature for big brown bats to
calculate values of daily energy expenditure from T
roost data because energy is a currency that likely affects reproductive fitness. We found no difference between maximum and minimum
T
roost, spatial variability in T
roost, or predicted energy expenditure in more-preferred vs less-preferred roosts. However, there was a significant difference
between T
roost and predicted energy expenditure when we compared occupied vs unoccupied roosts. The presence of bats increased T
roost by as much as 7°C, and there was a significant positive correlation between the number of bats occupying a roost, maximum
daily T
roost, and energy savings. We calculate that, on average, a normothermic individual would save about 6.5 kJ/day (roughly 9% of
the daily energy budget) by roosting in an occupied cavity relative to roosting alone and that savings may increase to 40 kJ/day
(about 53% of the energy budget) for an individual roosting in a group of 45 bats. Our findings suggest that variability in
microclimate among potential roost or nest sites may be less important to some cavity-dwelling endotherms than has been suggested
in previous studies. Our results reinforce the importance of sociality and social thermoregulation to the roosting ecology
of forest-living bats and socially roosting or nesting endotherms in general. 相似文献
402.
The advertisement call of frogs and toads is an example of multiple message signal because different acoustic properties encode
different kinds of biologically significant information. In the Italian treefrog, Hyla intermedia, pulse rate and frequency have been found to be under stabilizing female preferences and to encode information important
for mate recognition, whereas the number of calls per call group have been found to be under directional preferences and,
thus, to be important for mate quality assessment. In this study, we investigate preferences for calls that differ simultaneously
in frequency, pulse rate, and number of calls per call group, and we ask how these properties interact with each other in
influencing female mating decisions. Results of two-choice phonotaxis experiments provide no evidence to support the hypothesis
that females process multi-attribute signals in a hierarchical way. In contrast, the pattern of preferences is consistent
with the ‘preference function’ hypothesis, that is, with the hypothesis that females rank signals along an ordinal scale of
values and choose accordingly. Pulse rate and frequency influence mating preferences more than does the number of calls per
call group. The interaction between pulse rate and frequency is not additive but multiplicative: small differences in either
pulse rate or frequency that, alone, have no effects on female choice, interact synergistically so that their combination
has strong influence on female preferences. A preference repeatability test shows strong among-female differences in preference
for multi-attribute signals. We suggest that this result reveals not only a variation in attribute values among females, but
also a variation in the way females weight and combine attribute values into a single preference score. 相似文献
403.
Jari J. Ahtiainen Rauno V. Alatalo Raine Kortet Markus J. Rantala 《Behavioral ecology and sociobiology》2006,60(6):826-832
In this study, we provide a piece of experimental evidence that immune function is related to dominance and mating success in wild caught male wolf spiders, Hygrolycosa rubrofasciata. In the mating season, H. rubrofasciata males are actively searching for receptive females, and while searching males often engage in agonistic behavior (i.e., agonistic drumming signals, chases, and fights) with each other. The present results demonstrate that dominant males had higher lytic activities in their hemolymph than subordinates. Lytic activity estimates the concentration of antimicrobial peptides with lysozyme-like activity in hemolymph, which have been shown to play an important role in defense against bacteria, viruses, and fungi. Dominants also had higher courtship drumming rates than subordinates. Moreover, winners in mating competition had higher lytic activities than losers, but this was measured nonindependently of dominance status. Among males with mating failure, there was a moderate negative correlation between encapsulation rate and courtship drumming rate, suggesting that low quality males might not be able to bear the immunological costs of courtship behavior. These results suggest that females might gain immunological benefits by preferring vigorous males. 相似文献
404.
The problem of distinguishing density-independent (DI) from density-dependent (DD) demographic time series is important for understanding the mechanisms that regulate populations of animals and plants. We address this problem in a novel way by means of Statistical Learning Theory (SLT); SLT is built around the idea of VC-dimension, a complexity index for classes of parameterized functions. Though VC-dimensions of nonlinear models are generally unknown, in the linear case VC-dimension actually corresponds to the number of free parameters; this allows one to straightforwardly apply the model selection framework developed within SLT, and called Structural Risk Minimization (SRM). We generate noisy artificial time series, both DI and DD, and use SRM to recognize the model underlying the data, choosing among a suite of both density-dependent and independent demographies. We show that SRM significantly outperforms traditional model selection approaches, such as the Schwartz Information Criterion and Final Prediction Error in recognizing both density-dependence and independence. 相似文献
405.
Ultraviolet (UV) reflectance of the plumage is common in birds and plays an important role in sexual signalling. Recently,
it has been proposed that birds are able to modify plumage UV reflectance by the application of uropygial gland secretion.
Based on a survey of the optical properties of this secretion from 51 species belonging to 12 avian orders, we show that two
main types of uropygial secretions exist, one predominantly found in passerines and one in non-passerines, both reducing relative
UV reflectance of a white background (Teflon™ tape). We quantified how each type of secretion (exemplified by blue tit and
mallard) affected feather UV reflectance. Both secretions reduced overall brightness and relative UV reflectance of white
mallard feathers but hardly affected the reflectance of UV/blue blue tit crown feathers. According to models of avian colour
vision, changes in reflectance due to application of the secretion were at or below the discrimination threshold of most birds.
We conclude that the uropygial secretion is unlikely to play a major role in modifying plumage UV reflectance. However, the
optical properties of the uropygial secretion may have been selected to interfere as little as possible with visual signaling
through plumage reflectance.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
406.
In insects, large ejaculate and associated materials, including spermatophores, appear to have evolved via sexual selection acting on males to either delay female remating or to increase the rate of egg-laying. It is also possible, however, that females use nutrients transferred during mating to increase their lifetime fecundity. If so, male ejaculate size may also have evolved under natural selection as a form of paternal investment. In Lepidoptera, males with a greater number of prior matings tend to produce smaller spermatophores. However, the reported effects of male mating history on female fecundity vary widely among species. We therefore performed a meta-analysis using data from 29 studies of 25 species. Overall, the reproductive output of females mated to virgin males was significantly higher than that of females mated to sexually experienced males (Hedges d=0.33, P<0.01). A sample size of around 145 females per male mating type is required to detect an effect of this size with 80% statistical power at =0.05 (two-tailed). There was no difference in mean effect size between butterflies/skippers and moths. After controlling for any effect of taxonomic group, however, the mean effect size for polyandrous species was significantly greater than that for monandrous species (Hedges d=0.45 vs 0.25, P=0.01). We then discuss possible reasons why male mating history, presumably acting through its effect on spermatophore size, might have a stronger effect in polyandrous than monandrous species.Communicated by A. Cockburn 相似文献
407.
为优化危险废物填埋场地下水污染风险控制的工程/地质屏障参数,基于过程模型模拟-参数敏感性分析-参数优选的系统框架和方法,分析关键参数对于地下水中渗滤液所携带污染物浓度的影响和敏感性,基于分析结果推荐技术参数的取值区间和最低的技术参数要求.结果表明:①各参数对地下水污染风险的敏感性排序依次为导排支管间距>含水层厚度>导排层坡度>天然衬层渗透系数>导排层渗透系数>地下水流速.②当导排支管间距>25 m、导排层坡度 < 2%、导排层渗透系数 < 0.000 1 cm/s、天然衬层渗透系数>1×10-6 cm/s时,地下水污染风险急剧增大;反之,当导排支管间距 < 10 m、导排层坡度>3%、导排层渗透系数>0.01 cm/s、天然衬层渗透系数 < 5×10-7 cm/s时,对地下水污染风险的管控并无明显影响.③导排支管间距最低为25 m,但不宜 < 10 m,导排层坡度最低为2%,但不宜>3%,导排层渗透系数最低为0.01 cm/s,天然衬层渗透系数最低为1.0×10-6 cm/s.研究显示,现有标准中给出的参数取值具有合理性,但范围较广,应结合水文地质参数与填埋场参数确定. 相似文献
408.
409.
Megan Dailey Alix I. Gitelman Fred L. Ramsey Steve Starcevich 《Environmental and Ecological Statistics》2007,14(1):55-68
Models for the analysis of habitat selection data incorporate covariates in an independent multinomial selections model (McCracken
et al. 1998) Ramsey and Usner 2003 and an extension of that model to include a persistence parameter (2003). In both cases,
all parameters are assumed to be fixed through time. Radio telemetry data collected for habitat selection studies typically
consist of animal relocations through time, suggesting the need for an extension to these models. We use a Bayesian approach
that allows for the habitat selection probabilities, persistence parameter, or both, to change with season. These extensions
are particularly important when movement patterns are expected to differ seasonally and/or when availabilities of habitats
change throughout the study period due to weather or migration. We implement and compare the models using radio telemetry
data for westslope cutthroat trout in two streams in eastern Oregon. 相似文献
410.
Gabriele Gerlach Andrea Hodgins-Davis Bradley MacDonald Rebecca C. Hannah 《Behavioral ecology and sociobiology》2007,61(11):1765-1770
Zebrafish (Danio rerio) larvae prefer the olfactory cues of kin to non-kin. We examined the potential benefits of kin preference by comparing growth
rate, shoaling, and aggressive behavior in juvenile zebrafish housed in groups of either familiar kin or unfamiliar non-kin.
Over an observation period of 5 days, the animals grew 33% more in kin groups; however, neither shoaling nor the frequency
of aggressive interactions was different in groups of related versus unrelated individuals. Shoaling behavior increased with
increasing observation time and increasing age, while aggressive behavior remained the same. We conclude that associating
with kin probably creates a less stressful environment that allows for higher growth rates, which can lead to higher direct
fitness based on increased survival and earlier reproduction. Kin recognition leading to kin-structured groups may therefore
be under positive selection. 相似文献