全文获取类型
收费全文 | 10261篇 |
免费 | 19篇 |
国内免费 | 6篇 |
专业分类
安全科学 | 36篇 |
废物处理 | 791篇 |
环保管理 | 1304篇 |
综合类 | 1048篇 |
基础理论 | 3242篇 |
环境理论 | 2篇 |
污染及防治 | 1882篇 |
评价与监测 | 1046篇 |
社会与环境 | 927篇 |
灾害及防治 | 8篇 |
出版年
2024年 | 1篇 |
2023年 | 19篇 |
2022年 | 15篇 |
2021年 | 20篇 |
2020年 | 25篇 |
2019年 | 16篇 |
2018年 | 1490篇 |
2017年 | 1395篇 |
2016年 | 1232篇 |
2015年 | 154篇 |
2014年 | 54篇 |
2013年 | 61篇 |
2012年 | 512篇 |
2011年 | 1375篇 |
2010年 | 719篇 |
2009年 | 627篇 |
2008年 | 899篇 |
2007年 | 1255篇 |
2006年 | 26篇 |
2005年 | 40篇 |
2004年 | 48篇 |
2003年 | 73篇 |
2002年 | 109篇 |
2001年 | 20篇 |
2000年 | 16篇 |
1999年 | 7篇 |
1998年 | 19篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1985年 | 2篇 |
1984年 | 14篇 |
1983年 | 8篇 |
1981年 | 1篇 |
1972年 | 1篇 |
1964年 | 1篇 |
1935年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 671 毫秒
991.
992.
James A. R. Marshall 《Behavioral ecology and sociobiology》2011,65(3):503-512
Reconciling the evolution of altruism with Darwinian natural selection is frequently presented as a fundamental problem in
biology. In addition to an exponentially increasing literature on specific mechanisms that can permit altruism to evolve,
there has been a recent trend to establish general principles to explain altruism in populations undergoing natural selection.
This paper reviews and extends one approach to understanding the ultimate causes underlying the evolution of altruism and
mechanisms that can realise them, based on the Price equation. From the Price equation, we can see that such ultimate causes
equate to the different ways in which the frequency of an altruistic allele in a population can increase. Under this approach,
the ultimate causes underlying the evolution of altruism, given some positive fitness costs and benefits, are positive assortment
of altruistic alleles with the altruistic behaviour of others, positive deviations from additive fitness effects when multiple
altruists interact or bias in the inheritance of altruistic traits. In some cases, one cause can be interpreted in terms of
another. The ultimate causes thus identified can be realised by a number of different mechanisms, and to demonstrate its general
applicability, I use the Price equation approach to analyse a number of classical mechanisms known to support the evolution
of altruism (or cooperation): repeated interaction, ‘greenbeard’ traits, games played on graphs and payoff synergism. I also
briefly comment on other important points for the evolution of altruism, such as the ongoing debate over the predominant status
of inclusive fitness as the best way to understand its evolution. I conclude by arguing that analysing the evolution of altruism
in terms of its ultimate causes is the logical way to approach the problem and that, despite some of its technical limitations,
the Price equation approach is a particularly powerful way of doing so. 相似文献
993.
Recent studies have revealed the importance of self-consistency in evolutionary models, particularly in the context of male–female
interactions. This has been largely ignored in models of the ancestral divergence of the sexes, i.e., the evolution of anisogamy.
Here, we model the evolution of anisogamy in a Fisher-consistent context, explicitly taking into account the number of interacting
individuals in a typical reproductive group. We reveal an interaction between the number of adult individuals in the local
mating group and the selection pressures responsible for the divergence of the sexes. The same underlying model can produce
anisogamy in two different ways. Gamete competition can lead to anisogamy when it is relatively easy for gametes to find each
other, but when this is more difficult and gamete competition is absent, gamete limitation can provide another route for anisogamy
to evolve. In line with earlier models, organismal complexity favors anisogamy. We argue that the early contributions of Kalmus
and Scudo, largely dismissed as group selectionist, are valid under certain conditions. Linking their work with the contributions
of Parker helps to explain why precisely males keep producing more sperm than can ever lead to offspring: sperm could evolve
to provision zygotes but this brings little profit for the effort required, because sperm would have to be equipped with provisioning
ability before it is known which sperm will make it to the fertilization stage. This insight creates a logical link between
paternal care under uncertain paternity (where again investment is selected against when some investment never brings about
genetic benefits) and gamete size evolution. 相似文献
994.
Across animal taxa, exclusive female offspring care has evolved repeatedly from biparental care, suggesting that the latter
becomes evolutionarily unstable under certain conditions. Both the attributes of a species and the environment it experiences
can help to predict shifts from one particular care mode to another. Nevertheless, factors inducing differences in care strategies
among closely related species, or seasonal variation within species, have been subject to surprisingly little empirical testing.
Here, we report the results of a field-based study that examined both among and within species variation in mate desertion
in five species of closely related Nicaraguan cichlid fish in the genera Amphilophus and Amatitlania. The results show a link between female body size and male involvement in offspring care. Specifically, the larger the species
the less often males were found to provide extended care. Furthermore, we found that solitary females became more common towards
the end of the breeding season. We discuss the implications of this finding in the context of previous theoretical and empirical
contributions regarding the frequency of offspring desertion by males. 相似文献
995.
Subbiah Seenivasan NarayananNair Muraleedharan 《Environmental monitoring and assessment》2011,176(1-4):365-371
Tea is considered as a ‘health beverage’ due its antioxidant properties and resultant beneficial effects on human health. Such a beverage should be free from toxic elements such as pesticide residues and heavy metals. A large scale survey of teas produced in the tea factories of south India had been carried out for a period of three years from 2006 to 2008 and 912 tea samples were analysed for the residues of certain pesticides such as dicofol, ethion, quinalphos, hexaconazole, fenpropathrin, fenvalerate and propargite which are used for pest and disease control in tea in this part of the country. The analytical data proved that only less than 0.5 percentage of tea samples had residues of these pesticides. However, residues of pesticides were below their maximum limits in tea, stipulated by the European Union, Codex Alimentarius Commission of FAO/WHO and Prevention of Food Adulteration Act of Govt. of India. 相似文献
996.
Harshinie Karunarathna 《Journal of Coastal Conservation》2011,15(4):499-507
The long-term morphodynamic response of the Clyde Estuary to any possible change in environmental forcing associated with
global climate change and human interference is examined here using a model based on a systems approach. The model, which
uses Boolean Algebra as its formal mathematical language, provides a qualitative insight into the long term morphodynamic
behaviour of the estuarine system, at this level without the need for detailed and quantitative hydrodynamic and morphodynamic
process knowledge or extensive data resources. The model predictions suggest that the long-term morphological changes in the
Clyde Estuary largely depend on the fluvial flow of the River Clyde. Salt marshes in the upper reaches of the estuary were
found to be the most vulnerable morphological feature of the estuary. In the event of increased river flow in the future,
a likely situation according to climate change scenarios, saltmarshes will deplete or disappear altogether, irrespective of
the sediment influx into the estuary. Changes to waves and tides will also contribute to the evolution by taking the estuary
through significantly different intermediate morphological states whilst evolving towards a stable end state. 相似文献
997.
An open channel flow with a flow depth close to the critical depth is characterised by a curvilinear streamline flow field
that results in steady free surface undulations. Near critical flows of practical relevance encompass the undular hydraulic
jump when the flow changes from supercritical (F > 1) to subcritical (F < 1), and the undular weir flow over broad-crested
weirs where the flow changes from subcritical (F < 1) to supercritical (F > 1). So far these flows were mainly studied based
on ideal fluid flow computations, for which the flow is assumed irrotational and, thus, shear forces are absent. While the
approach is accurate for critical flow conditions (F = 1) in weir and flumes, near-critical flows involve long distances reaches,
and the effect of friction on the flow properties cannot be neglected. In the present study the characteristics of near-critical
free-surface flows are reanalysed based on a model accounting for both the streamline curvature and friction effects. Based
on the improved model, some better agreement with experimental results is found, thereby highlighting the main frictional
features of the flow profiles. 相似文献
998.
Jorge Alberto Achcar Josmar Mazucheli Emílio Augusto Coelho-Barros 《Environmental and Ecological Statistics》2011,18(2):315-329
In this paper we present a hierarchical Bayesian analysis for a predator–prey model applied to ecology considering the use
of Markov Chain Monte Carlo methods. We consider the introduction of a random effect in the model and the presence of a covariate
vector. An application to ecology is considered using a data set related to the plankton dynamics of lake Geneva for the year
1990. We also discuss some aspects of discrimination of the proposed models. 相似文献
999.
Objectives
Motorcycle registrations have risen in recent years. Although motorcyclist crash fatalities in 2009 were 16% lower than in 2008, they were double the number of deaths in 1997. The present study examined current motorcyclists’ travel patterns and views of motorcycle helmets and other safety topics.Methods
Motorcycle drivers were interviewed in a national telephone survey conducted in 2009. A weighted sample of 1,606 motorcyclists resulted from adjusting for the oversampling of those younger than 40 and those in the three states without a motorcycle helmet use law (Illinois, Iowa, New Hampshire). All analyses were based on the weighted sample, which was intended to result in a nationally representative sample of motorcyclists.Results
About one-quarter of respondents said they did not always wear helmets. Of these respondents, 57% said a law requiring helmet use would persuade them to do so, and 27% said nothing would. Ninety-four percent of respondents in states with universal helmet laws said they always ride helmeted, compared with about half of respondents in other states. About half of all respondents favored these laws. About three-quarters said they believe helmets keep riders safer, including two-thirds of respondents who oppose universal laws and almost half of drivers who rarely/never wear helmets. Drivers ages 18–29 and drivers of sport/unclad sport, sport touring, and super sport motorcycles were more likely to always wear helmets, support universal helmet laws, and believe helmets keep riders safer. About half of respondents said antilock braking systems (ABS) enhance safety and that they would get ABS on their next motorcycle. Less than one-quarter thought an airbag would protect a motorcyclist in a crash, and even fewer would consider getting one on their next motorcycle. Forty-three percent of motorcyclists said they had crashed at least once; 62% of the most recent crashes involved no vehicles besides the motorcycle. Respondents reported riding their motorcycles about 5,400 miles, on average, during the past year. Drivers ages 18–29 reported riding fewer miles, on average, than older drivers and more often rode at night and to/from work or school. Drivers of touring and sport touring motorcycles traveled more miles and took more long trips.Conclusions
Motorcyclists’ travel patterns and views vary widely, but there are distinct patterns by driver age and motorcycle type. Drivers who believe helmets keep riders safer are more likely to always wear them, but this belief appears insufficient to motivate some drivers to wear them. However, universal helmet laws appear effective in increasing helmet use. Many drivers are receptive to purchasing ABS on their next motorcycle.Impact on industry
States should be encouraged to enact universal helmet laws, and motorcycle manufacturers should be encouraged to offer ABS. 相似文献1000.
Armando A. Rodriguez Oguzhan Cifdaloz John Martin Anderies Marco A. Janssen Jeffrey Dickeson 《Environmental Modeling and Assessment》2011,16(1):15-36
This paper presents a framework for the study of policy implementation in highly uncertain natural resource systems in which
uncertainty cannot be characterized by probability distributions. We apply the framework to parametric uncertainty in the
traditional Gordon–Schaefer model of a fishery to illustrate how performance can be sacrificed (traded-off) for reduced sensitivity
and hence increased robustness, with respect to model parameter uncertainty. With sufficient data, our robustness–vulnerability
analysis provides tools to discuss policy options. When less data are available, it can be used to inform the early stages
of a learning process. Several key insights emerge from this analysis: (1) the classic optimal control policy can be very
sensitive to parametric uncertainty, (2) even mild robustness properties are difficult to achieve for the simple Gordon–Schaefer
model, and (3) achieving increased robustness with respect to some parameters (e.g., biological parameters) necessarily results
in increased sensitivity (decreased robustness) with respect to other parameters (e.g., economic parameters). We thus illustrate
fundamental robustness–vulnerability trade-offs and the limits to robust natural resource management. Finally, we use the
framework to explore the effects of infrequent sampling and delays on policy performance. 相似文献