全文获取类型
收费全文 | 1024篇 |
免费 | 52篇 |
国内免费 | 98篇 |
专业分类
安全科学 | 103篇 |
废物处理 | 19篇 |
环保管理 | 303篇 |
综合类 | 202篇 |
基础理论 | 340篇 |
环境理论 | 1篇 |
污染及防治 | 82篇 |
评价与监测 | 57篇 |
社会与环境 | 47篇 |
灾害及防治 | 20篇 |
出版年
2023年 | 16篇 |
2022年 | 14篇 |
2021年 | 32篇 |
2020年 | 31篇 |
2019年 | 21篇 |
2018年 | 15篇 |
2017年 | 21篇 |
2016年 | 37篇 |
2015年 | 24篇 |
2014年 | 26篇 |
2013年 | 60篇 |
2012年 | 29篇 |
2011年 | 72篇 |
2010年 | 46篇 |
2009年 | 78篇 |
2008年 | 61篇 |
2007年 | 58篇 |
2006年 | 76篇 |
2005年 | 57篇 |
2004年 | 36篇 |
2003年 | 35篇 |
2002年 | 40篇 |
2001年 | 27篇 |
2000年 | 34篇 |
1999年 | 14篇 |
1998年 | 23篇 |
1997年 | 14篇 |
1996年 | 15篇 |
1995年 | 14篇 |
1994年 | 11篇 |
1993年 | 9篇 |
1991年 | 4篇 |
1990年 | 7篇 |
1989年 | 8篇 |
1988年 | 6篇 |
1987年 | 9篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1983年 | 6篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 12篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1975年 | 3篇 |
1973年 | 5篇 |
1972年 | 7篇 |
1971年 | 5篇 |
1970年 | 3篇 |
排序方式: 共有1174条查询结果,搜索用时 343 毫秒
811.
The research activities in the project Assessing the Influence of Real Releases on Explosions (AIRRE) included a unique series of large-scale explosion experiments with high-momentum jet releases directed into congested geometries with subsequent ignition. The primary objective for the AIRRE project was to gain improved understanding of the effect that realistic releases and turbulent flow conditions have on the consequences of accidental gas explosions in the petroleum industry. A secondary objective was to develop a methodology that can facilitate safe and optimal design of process facilities. This paper presents selected results from experiments involving ignition of a highly turbulent gas cloud, generated by a large-scale, pressurised release of natural gas. The paper gives an overview of the effect on maximum explosion overpressures of varying the ignition position relative to the release point of the jet and a congested region placed inside the flammable cloud, with either a high or a medium level of congestion. For two of the tests, involving a jet release and the medium congestion rig, the maximum overpressures significantly exceeded those obtained in a quiescent reference test. The paper presents detailed results for selected tests and discusses the effect of the initial flow field generated by realistic releases – including turbulence, net flow and concentration gradients – on relevant explosion phenomena. 相似文献
812.
腈醛混合化合物对发光菌联合毒性的QSAR研究 总被引:5,自引:1,他引:5
测定了羟基乙腈与系列醛类化合物和对苯二甲醛与系列腈类化合物对发光菌(Photobacterium phosphoreum)的联合毒性,探讨了腈醛混合化合物对发光菌的联合毒性机制,并尝试提出了腈醛混合化合物对发光菌联合毒性的QSAR模型.结果表明,不同的腈醛混合化合物对发光菌的联合毒性不同,联合毒性的大小与腈类化合物和醛类化合物之间化学相互作用的程度紧密相关,采用QSAR模型TU=0.842—0.831σ。(n=8,r^2=0.803,SE=0.222,F=24.415,P=0.003)和TU=-0.348—8.450C^*(n=8,r^2=0.874,SE=0.219,F=41.730,P=0.001)分别定量描述羟基乙腈与系列醛类化合物和对苯二甲醛与系列腈类化合物对发光菌的联合毒性.模型具有较高的稳定性和预测能力. 相似文献
813.
广东沼气农业模式的典型调查与思考 总被引:9,自引:0,他引:9
回顾了广东沼气发展历程,介绍了广东典型沼气农业模式,包括广东西南部丘陵区典型农户沼气模式,广东东部丘陵区典型农户沼气模式,广东东北部丘陵山区典型农户沼气模式,广东低洼地和积水区农户沼气模式,以及广东规模化养殖场沼气模式,并在此基础上分析了沼气农业模式的空间分布规律、沼气模式和经济发展的关系以及沼气发展的系统工程。 相似文献
814.
Infectious pancreatic necrosis virus (IPNV) is an increasingly common pathogen in farmed Scottish Atlantic salmon; over 80% of marine sites are now infected, although most do not suffer clinical disease. The increasing prevalence of this pathogen in farms over the period 1996–2003 is modelled using a simple susceptible–infected (SI) epidemic model. Because salmon production approximately doubled over this period, population-dependent and -independent transmission models are compared. The model generates mean R0 (increase ratio) of 1.41 in fresh and 1.45 in marine water farms at the national level; higher values apply with time under population-dependent transmission (1.58, freshwater, 1.80 marine by 2003). Regional differences in R0 are mostly moderate, indicating similar regional processes in spite of substantial difference in prevalence. Prevalence of IPNV for marine sites was further increased by the use of smolts (young salmon) from multiple freshwater sources. The model suggests that prevalence is entering dynamic equilibrium and will stabilise or only increase slowly as population increases. Cutting freshwater transmission is the most effective single strategy at reducing IPNV prevalence, but a combination of strategies (including reducing the number of sources of smolts) is better and indeed is required for eradication. Eradication would require cuts in transmission of at least 30–45% and this is unlikely to be practicable. 相似文献
815.
Jeffrey H. Gove Ernst Linder Walter M. Tzilkowski 《Environmental and Ecological Statistics》1996,3(1):65-80
The possibility of a bimodal log-likelihood function arises with certain data when the combined removal and signs-of-activities estimator is used. Bimodal log-likelihoods may, in turn, yield disjoint confidence intervals for certain confidence levels. The hypothesis that bimodality is caused by the violation of the equal catchability assumption of the removal model, leading to the combination of contradictory data/models in the combined estimator is set forth. Simulations exploring the effect of the violation of removal model assumptions on estimation and inference showed that the assumption of unequal capture probability influenced the frequency of bimodal likelihoods; similarly, extreme parameter values for probability of capture influenced the number of excessively large confidence intervals produced. A sex-specific combined estimator is developed as a remedial model tailored to the problem. The simulations suggest that both the signs-of-activities estimator and the sex-specific estimator perform equally well over the range of simulations presented, though the signs-of-activities estimator is easier to implement. 相似文献
816.
Male European starlings Sturnus vulgaris sing long complex songs that appear to be important in the courtship of females but which also influence competitive interactions
between males. We tested the hypothesis that females choose mates on the basis of the complexity of their songs, rather than
on the quality of the territories the males defended. In order to determine whether certain territories were preferred over
others, the first set of birds to settle in the experimental nest-boxes was removed and a second set allowed to settle. Consistent
preferences for certain nest-boxes were indicated by correlations between the settlement patterns of the first and second
sets of birds. However, males with the most complex song did not necessarily occupy the most preferred nest sites. Males with
more complex song acquired mates faster. This relationship remained significant when nest-site preference was statistically
controlled, indicating that female starlings chose males with complex song rather than those that defended preferred nest
sites. A number of morphological variables were also found to be uncorrelated with female choice. Song complexity in European
starlings increases with age, and the evolution of song complexity in this species is consistent with an age-indicator model
of sexual selection. Males with larger repertoires were also in better condition, indicating that females obtain high-quality
mates by choosing on the basis of male song.
Received: 29 April 1995/Accepted after revision: 9 September 1995 相似文献
817.
Ijaz?M.?KhanEmail author Richard?R.?Simons Anthony?J.?Grass 《Environmental Fluid Mechanics》2005,5(5):393-413
Experiments have been carried out to investigate turbulence at and above roof-level in an urban environment, and to predict
the behaviour of street pollution from experiments using dye dispersion, for different roughness conditions and bed geometries.
The flow in the boundary layer above an idealised urban environment has been simulated in a laboratory water flume. Comparisons
have been made for the same model street canyon with and without the presence of upstream roughness. In the tests reported
here, model street canyons were aligned perpendicular to the flow direction, and velocity measurements made within and above
the model street canyons using a laser Doppler velocimeter (LDV). Flow visualisation techniques have also been used to confirm
the gross flow features from streak images. Turbulence generated from the upstream roughness has a significant effect on the
turbulence production and dispersion behaviour of the dye simulating pollution in street canyons. 相似文献
818.
Abstract: Recovery of endangered species in highly fragmented habitats often requires habitat restoration. Selection of restoration sites typically involves too many options and too much uncertainty to reach a decision based on existing reserve design methods. The Fender's blue butterfly ( Icaricia icarioides fenderi ) survives in small, isolated patches of remnant prairie in Oregon's Willamette Valley—a habitat for which <0.5% of the original remains. Recovery of this species will require considerable habitat restoration. We investigated the potential of biologically based rules of thumb and more complex models to serve as tools in making land acquisitions. Based on Fender's blue dispersal behavior and demography, we have estimated that restored patches should be <1 km from existing habitat and at least 2 ha. We compared these rules to the results of two modeling approaches: an incidence function model and a spatially explicit simulation of demography and dispersal behavior. Not surprisingly, the simple rules and complex models all conclude that large (>2 ha) connected (<1 km) patches have the highest restoration value. The dispersal model, however, suggests that small, connected patches have more restoration value than large, isolated patches, whereas the incidence function model suggests that size and connectivity are equally important. These differences stem from model assumptions. We used incidence functions to predict long-term, stochastic, steady-state conditions and dispersal simulations to predict short-term (25-year) colonization dynamics. To apply our results in the context of selecting restoration sites on the ground, we recommend selecting nearby sites when short-term colonization dynamics are expected to be an important aspect of a species' biology. 相似文献
819.
Demographic Limitations of the Ability of Habitat Restoration to Rescue Declining Populations 总被引:1,自引:0,他引:1
Abstract: Habitat restoration is often recommended in conservation without first evaluating whether populations are in fact habitat limited and thus whether declining populations can be stabilized or recovered through habitat restoration. We used a spatially structured demographic model coupled with a dynamic neutral landscape model to evaluate whether habitat restoration could rescue populations of several generic migratory songbirds that differed in their sensitivity to habitat fragmentation (i.e., severity of edge effects on nesting success). Simulating a best-case scenario, landscapes were instantly restored to 100% habitat before, at, or after habitat loss exceeded the species' vulnerability threshold. The vulnerability threshold is a measure of extinction risk, in which the change in population growth rate ( δλ ) scaled to the rate of habitat loss ( δh ) falls below −1% ( δλ/δh ≤ −0.01). Habitat restoration was most effective for species with low-to-moderate edge sensitivities and in landscapes that had not previously experienced extensive fragmentation. To stabilize populations of species that were highly edge sensitive or any species in heavily fragmented landscapes, restoration needed to be initiated long before the vulnerability threshold was reached. In practice, habitat restoration is generally not initiated until a population is at risk of extinction, but our model results demonstrate that some populations cannot be recovered at this point through habitat restoration alone. At this stage, habitat loss and fragmentation have seriously eroded the species' demographic potential such that halting population declines is limited more by demographic factors than the amount of available habitat. Evidence that populations decline in response to habitat loss is thus not sufficient to conclude that habitat restoration will be sufficient to rescue declining populations. 相似文献
820.
Importance of Well-Designed Monitoring Programs for the Conservation of Endangered Species: Case Study of the Snail Kite 总被引:1,自引:0,他引:1
Abstract: Monitoring natural populations is often a necessary step to establish the conservation status of species and to help improve management decisions. Nevertheless, many monitoring programs do not effectively address primary sources of variability in monitoring data, which ultimately may limit the utility of monitoring in identifying declines and improving management. To illustrate the importance of taking into account detectability and spatial variation, we used a recently proposed estimator of abundance (superpopulation estimator) to estimate population size of and number of young produced by the Snail Kite ( Rostrhamus sociabilis plumbeus ) in Florida. During the last decade, primary recovery targets set by the U.S. Fish and Wildlife Service for the Snail Kite that were based on deficient monitoring programs (i.e., uncorrected counts) were close to being met (by simply increasing search effort during count surveys). During that same period, the Snail Kite population declined dramatically (by 55% from 1997 to 2005) and the number of young decreased by 70% between 1992–1998 and 1999–2005. Our results provide a strong practical case in favor of the argument that investing a sufficient amount of time and resources into designing and implementing monitoring programs that carefully address detectability and spatial variation is critical for the conservation of endangered species. 相似文献