全文获取类型
收费全文 | 34480篇 |
免费 | 344篇 |
国内免费 | 457篇 |
专业分类
安全科学 | 954篇 |
废物处理 | 1625篇 |
环保管理 | 4264篇 |
综合类 | 5457篇 |
基础理论 | 9449篇 |
环境理论 | 18篇 |
污染及防治 | 8501篇 |
评价与监测 | 2384篇 |
社会与环境 | 2451篇 |
灾害及防治 | 178篇 |
出版年
2023年 | 140篇 |
2022年 | 322篇 |
2021年 | 316篇 |
2020年 | 240篇 |
2019年 | 284篇 |
2018年 | 887篇 |
2017年 | 896篇 |
2016年 | 1068篇 |
2015年 | 607篇 |
2014年 | 891篇 |
2013年 | 2416篇 |
2012年 | 1234篇 |
2011年 | 2042篇 |
2010年 | 1498篇 |
2009年 | 1559篇 |
2008年 | 1919篇 |
2007年 | 2128篇 |
2006年 | 1263篇 |
2005年 | 1160篇 |
2004年 | 1012篇 |
2003年 | 1148篇 |
2002年 | 1051篇 |
2001年 | 1248篇 |
2000年 | 872篇 |
1999年 | 521篇 |
1998年 | 365篇 |
1997年 | 359篇 |
1996年 | 356篇 |
1995年 | 423篇 |
1994年 | 446篇 |
1993年 | 352篇 |
1992年 | 374篇 |
1991年 | 352篇 |
1990年 | 386篇 |
1989年 | 341篇 |
1988年 | 296篇 |
1987年 | 278篇 |
1986年 | 223篇 |
1985年 | 249篇 |
1984年 | 274篇 |
1983年 | 261篇 |
1982年 | 241篇 |
1981年 | 222篇 |
1980年 | 175篇 |
1979年 | 194篇 |
1978年 | 176篇 |
1975年 | 140篇 |
1974年 | 117篇 |
1972年 | 130篇 |
1971年 | 131篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
In the past decade Australia has experienced a series of large‐scale, severe natural disasters including catastrophic bushfires, widespread and repeated flooding, and intense storms and cyclones. There appears to be a prima facie case for rebuilding damaged infrastructure to a more disaster resilient (that is, to ‘betterment’) standard. The purpose of this paper is to develop and illustrate a consistent and readily applied method for advancing proposals for the betterment of essential public assets, which can be used by governments at all levels to determine the net benefits of such proposals. Case study results demonstrate that betterment investments have the potential to deliver a positive economic return across a range of asset types and regions. Results, however, are highly sensitive to underlying assumptions; in particular the probability of the natural disaster affecting the infrastructure in the absence of betterment. 相似文献
992.
To investigate the ability of elasmobranchs to distinguish between differing prey-type electric fields we examined the electroreceptive
foraging behaviour of a model species, Scyliorhinus canicula (small-spotted catshark). Catshark preferences were studied by behaviourally conditioning them to swim through narrow tunnels,
and on exit presenting them simultaneously with two different electric fields. Their subsequent choices of the following paired
options were recorded; (i) Two artificial electric fields (dipole electrodes) with different magnitude direct current (D.C.),
(ii) Two artificial electric fields, one D.C. and the other alternating current (A.C.), of the same magnitude, and (iii) similar
magnitude, natural and artificial D.C. electric fields associated with shore crabs and dipole electrodes respectively. We
found a highly significant preference for the stronger D.C. electric field and a less pronounced, but still significant, preference
for the A.C. electric field rather than the D.C. electric field. No preference was demonstrated between the artificial and
natural D.C. electric fields. The findings are discussed in relation to the animal’s diet and ecology and with regard to anthropogenic
sources of electric fields within their habitat. 相似文献
993.
Spawning female blue crabs, Callinectes sapidus, use ebb-tide transport (ETT) to migrate seaward. In estuaries with semi-diurnal tides, ETT in ovigerous blue crabs is driven
by a circatidal rhythm in vertical swimming in which crabs ascend into the water column during ebb tide. The ontogeny of this
rhythm was examined by monitoring swimming behavior of females before the pubertal molt, females that had recently undergone
the molt but had not yet produced a clutch of eggs, and ovigerous females from an estuary with strong semi-diurnal tides.
To assess variation in swimming rhythms with ambient tidal regime, swimming rhythms of ovigerous females from semi-diurnal
(Beaufort, North Carolina), diurnal (St. Andrew Bay, Florida), and non-tidal (South River, North Carolina) estuaries were
compared. Experiments were conducted during the summers of 2006–2008. Female crabs prior to oviposition had variable endogenous
swimming rhythms (circadian, circatidal, or circalunidian). Ovigerous females from estuaries with semi-diurnal and diurnal
tides had pronounced circatidal or circalunidian rhythms with swimming during the time of ambient ebb tide. Swimming rhythms
of several ovigerous crabs switched between circatidal and circalunidian during the ~5-day observation period. Ovigerous crabs
from a non-tidal estuary had a circadian rhythm with vertical swimming around the time of sunset. These results suggest that,
while endogenous swimming rhythms are present in some female blue crabs prior to oviposition, rapid seaward movement via ETT
in tidal estuaries begins following oviposition of the first clutch of eggs. 相似文献
994.
Claire M. Waluda Martin A. Collins Andrew D. Black Iain J. Staniland Philip N. Trathan 《Marine Biology》2010,157(1):99-112
Antarctic fur seals Arctocephalus gazella and macaroni penguins Eudyptes chrysolophus are the two main land-based krill Euphausia superba consumers in the northern Scotia Sea. Using a combination of concurrent at-sea (predator observations, net hauls and multi-frequency
acoustics), and land-based (animal tracking and diet analysis) techniques, we examined variability in the foraging ecology
of these sympatric top predators during the austral summer and autumn of 2004. Krill availability derived from acoustic surveys
was low during summer, increasing in autumn. During the breeding season, krill occurred in 80% of fur seal diet samples, with
fish remains in 37% of samples. Penguin diets contained the highest proportion of fish in over 20 years of routine monitoring
(46% by mass; particularly the myctophid Electrona antarctica), with krill (33%) and amphipods (Themisto gaudichaudii; 21%) also occurring. When constrained by the need to return and feed their offspring both predator species foraged to the
northwest of South Georgia, consistent with an area of high macrozooplankton biomass, but fur seals were apparently more successful
at exploiting krill. When unconstrained by chick-rearing (during March) penguins foraged close to the Shag Rocks shelf-break,
probably exploiting the high daytime biomass of fish in this area. Penguins and seals are able to respond differently to periods
of reduced krill abundance (in terms of variability in diet and foraging behaviour), without detriment to the breeding success
of either species. This highlights the importance of myctophid fish as an alternative trophic pathway for land-based predators
in the Scotia Sea ecosystem. 相似文献
995.
Chukwujindu M. A. Iwegbue Godwin E. Nwajei Jude E. Ogala Chukwudumebi L. Overah 《Environmental geochemistry and health》2010,32(5):415-430
The concentrations of trace metals (Cd, Pb, Cu, Cr, Fe, Ni, Zn and Co) were studied in soil profiles of eight municipal waste dump sites in Warri metropolis. The results indicate that concentrations of trace metals varied widely among the different dumpsites and decreased with depths in a studied soil profile. The accumulation pattern for the heavy metals in the soil profiles follows the order: Fe > Pb > Mn > Co > Cr > Zn > Ni > Cu > Cd. The concentrations of metals found in these sites was below the Canadian remediation criteria for land for agricultural, residential and commercial/industrial purposes except for the cadmium levels in some sites that exceeded criterion values for agricultural and residential. In such sites, remedial actions are required before any form of chosen development can take place. The levels of heavy metals found in these dump sites were higher than that of the control site. The examined metals showed no significant correlation with soil physicochemical properties at the surface horizon, which is suggestive evidence that these metals arise from anthropogenic input. 相似文献
996.
Alecos Demetriades Xiangdong Li Michael H. Ramsey Iain Thornton 《Environmental geochemistry and health》2010,32(6):529-552
In the Lavrion urban area study, Hellas, a five-step sequential extraction method was applied on samples of ‘soil’ (n = 224), affected by long-term mining and metallurgical activities, and house dust (n = 127), for the purpose of studying the potential bioaccessibility of lead and other metals to humans. In this paper, the
Pb concentrations in soil and house dust samples are discussed, together with those in rocks and children’s blood. Lead is
mainly associated with the carbonate, Fe–Mn oxides and residual fractions in soil and house dust. Considering the very low
pH of gastric fluids (1–3), a high amount of metals, present in soil (810–152,000 mg/kg Pb) and house dust (418–18,600 mg/kg Pb),
could be potentially bioaccessible. Consequently, children in the neighbourhoods with a large amount of metallurgical processing
wastes have high blood-Pb concentrations (5.98–60.49 μg/100 ml; median 17.83 μg/100 ml; n = 235). It is concluded that the Lavrion urban and sub-urban environment is extremely hazardous to human health, and the
Hellenic State authorities should urgently tackle this health-related hazard in order to improve the living conditions of
local residents. 相似文献
997.
This paper presents a scan statistic, progressive upper level set (PULSE) scan statistic, for geospatial hotspot detection
and its software implementation. Like ULS, the PULSE scan statistic is based on the arbitrarily shaped scan window and can
be adapted for a network setting. PULSE is a refinement of the upper level set (ULS) scan statistic. Like some other likelihood
based scanning devices, the ULS scan statistic identifies maximum likelihood estimate (MLE) zones that tend to be ‘stringy’
and sprawling. Its search path increases possibility of inclusion of extraneous cells in its MLE zones and, to a smaller extent,
of exclusion of cells that belong to a true hotspot from its MLE zone. The PULSE scan statistic achieves improvement over
the ULS scan statistic in two ways. First, it begins its search for a most likely zone with a large population of candidate
zones obtained by modifying the ULS tree structure and continues its search using a genetic algorithm. Secondly, to reduce
chances of generating an MLE that is excessively stringy and that includes extraneous cells in the MLE zone, PULSE uses cardinality
and compactness of zones along with their likelihoods as the fitness function in the genetic algorithm and uses several pertinent
criteria including evenness of intra-zone cellular response ratios to determine the MLE zone. To reduce computation, Gumbel
distribution of extreme values is used to determine the p-value of the MLE zone. Better results come at the cost of increased processing time. An evaluative performance study is presented. 相似文献
998.
Dianne L. Watson Euan S. Harvey Ben M. Fitzpatrick Timothy J. Langlois George Shedrawi 《Marine Biology》2010,157(6):1237-1250
Measures of fish abundance, assemblage composition and length were compared when sampled by baited remote underwater stereo-video
(stereo BRUV) and diver-operated stereo-video transects (stereo DOV) at the Houtman Abrolhos Islands and Ningaloo Reef. Species
richness counts were 40% higher on stereo BRUV than stereo DOV. Stereo BRUVs also recorded a greater number of large-bodied
targeted species in higher abundance than stereo DOV (e.g. Lethrinus nebulosus, Plectropomus leopardus) at the Houtman Abrolhos and at Ningaloo Reef. Many non-targeted species were also recorded in greater abundances on stereo
BRUV than stereo DOV (e.g. Coris auricularis, Gymnothorax spp). Stereo DOV transects recorded a greater abundance of some small-bodied Pomacentridae, Labridae and Scaridae species
than did stereo BRUV, particularly at Ningaloo Reef. This study demonstrates that choice of sampling technique for surveys
of reef fish can lead to very different biological interpretations of fish assemblage structure. 相似文献
999.
Lorien Pichegru Peter G. Ryan Robert J. M. Crawford Carl D. van der Lingen David Grémillet 《Marine Biology》2010,157(3):537-544
In variable environments, organisms are bound to track environmental changes if they are to survive. Most marine mammals and
seabirds are colonial, central-place foragers with long-term breeding-site fidelity. When confronted with environmental change,
such species are potentially constrained in their ability to respond to these changes. For example, if environmental conditions
deteriorate within their limited foraging range, long-lived species favour adult survival and abandon their current breeding
effort, which ultimately influences population dynamics. Should poor conditions persist over several seasons, breeding-site
fidelity may force animals to continue breeding in low-quality habitats instead of emigrating towards more profitable grounds.
We assessed the behavioural response of a site-faithful central-place forager, the Cape gannet Morus capensis, endemic to the Benguela upwelling system, to a rapid shift in the distribution and abundance of its preferred prey, small
pelagic shoaling fish. We studied the distribution and the abundance of prey species, and the diet, foraging distribution,
foraging effort, energy requirements, and breeding success of gannets at Malgas Island (South Africa) over four consecutive
breeding seasons. Facing a rapid depletion of preferred food within their foraging range, Cape gannets initially increased
their foraging effort in search of their natural prey. However, as pelagic fish became progressively scarcer, breeding birds
resorted to scavenging readily available discards from a nearby demersal fishery. Their chicks cannot survive on such a diet,
and during our 4-year study, numbers of breeding birds at the colony decreased by 40% and breeding success of the remaining
birds was very low. Such behavioural inflexibility caused numbers of Cape gannets breeding in Namibia to crash by 95% following
over-fishing of pelagic fish in the 1970s. In the context of rapid environmental changes, breeding-site fidelity of long-lived
species may increase the risk of local or even global extinction, rendering these species particularly vulnerable to global
change. 相似文献
1000.
The extent to which genetic divergence can occur in the absence of physical barriers to gene flow is currently one of the most controversial topics in evolutionary biology, with implications for our understanding of speciation, phenotypic plasticity and adaptive potential. This is illustrated by a recent study reporting a surprising pattern of genetic differentiation between intertidal and subtidal morphotypes of the broadcast-spawning Antarctic limpet Nacella concinna. To explore this further, we collected almost 400 Antarctic limpets from four depths (intertidal, 6, 15 and 25 m) at Adelaide island, Antarctica, and conducted a combined morphometric and genetic analysis using 168 polymorphic amplified fragment length polymorphism (AFLP) loci. Morphological analysis revealed not only pronounced differences between the two morphotypes, but also a continuous cline in shell shape from the intertidal zone down to 25 m depth, suggesting that the distinction between the morphotypes may be artificial. Moreover, genetic analysis using both F st and a Bayesian analogue found no evidence for differentiation either between the two morphotypes or by depth, and a Bayesian cluster analysis did not detect any cryptic genetic structure. Our findings lend support to the notion that limpets can be phenotypically highly plastic, although further studies are required to determine unequivocally whether there is any genetic basis to the observed variation in shell morphology. 相似文献