全文获取类型
收费全文 | 2268篇 |
免费 | 141篇 |
国内免费 | 422篇 |
专业分类
安全科学 | 54篇 |
废物处理 | 16篇 |
环保管理 | 238篇 |
综合类 | 915篇 |
基础理论 | 871篇 |
环境理论 | 1篇 |
污染及防治 | 132篇 |
评价与监测 | 47篇 |
社会与环境 | 514篇 |
灾害及防治 | 43篇 |
出版年
2024年 | 2篇 |
2023年 | 38篇 |
2022年 | 47篇 |
2021年 | 58篇 |
2020年 | 48篇 |
2019年 | 73篇 |
2018年 | 52篇 |
2017年 | 85篇 |
2016年 | 100篇 |
2015年 | 97篇 |
2014年 | 86篇 |
2013年 | 210篇 |
2012年 | 132篇 |
2011年 | 220篇 |
2010年 | 183篇 |
2009年 | 117篇 |
2008年 | 149篇 |
2007年 | 173篇 |
2006年 | 150篇 |
2005年 | 124篇 |
2004年 | 107篇 |
2003年 | 80篇 |
2002年 | 75篇 |
2001年 | 65篇 |
2000年 | 58篇 |
1999年 | 47篇 |
1998年 | 36篇 |
1997年 | 26篇 |
1996年 | 27篇 |
1995年 | 40篇 |
1994年 | 18篇 |
1993年 | 32篇 |
1992年 | 8篇 |
1991年 | 18篇 |
1990年 | 5篇 |
1989年 | 10篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1986年 | 5篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1971年 | 2篇 |
排序方式: 共有2831条查询结果,搜索用时 296 毫秒
191.
Abstract: Understanding the way in which habitat fragmentation disrupts animal dispersal is key to identifying effective and efficient conservation strategies. To differentiate the potential effectiveness of 2 frequently used strategies for increasing the connectivity of populations in fragmented landscapes—corridors and stepping stones—we combined 3 complimentary methods: behavioral studies at habitat edges, mark‐recapture, and genetic analyses. Each of these methods addresses different steps in the dispersal process that a single intensive study could not address. We applied the 3 methods to the case study of Atrytonopsis new species 1, a rare butterfly endemic to a partially urbanized stretch of barrier islands in North Carolina (U.S.A.). Results of behavioral analyses showed the butterfly flew into urban and forested areas, but not over open beach; mark‐recapture showed that the butterfly dispersed successfully through short stretches of urban areas (<500 m); and genetic studies showed that longer stretches of forest (>5 km) were a dispersal barrier, but shorter stretches of urban areas (≤5 km) were not. Although results from all 3 methods indicated natural features in the landscape, not urbanization, were barriers to dispersal, when we combined the results we could determine where barriers might arise: forests restricted dispersal for the butterfly only when there were long stretches with no habitat. Therefore, urban areas have the potential to become a dispersal barrier if their extent increases, a finding that may have gone unnoticed if we had used a single approach. Protection of stepping stones should be sufficient to maintain connectivity for Atrytonopsis new species 1 at current levels of urbanization. Our research highlights how the use of complementary approaches for studying animal dispersal in fragmented landscapes can help identify conservation strategies. 相似文献
192.
Reintroductions are increasingly used to reestablish species, but a paucity of long‐term postrelease monitoring has limited understanding of whether and when viable populations subsequently persist. We conducted temporal genetic analyses of reintroduced populations of swift foxes (Vulpes velox) in Canada (Alberta and Saskatchewan) and the United States (Montana). We used samples collected 4 years apart, 17 years from the initiation of the reintroduction, and 3 years after the conclusion of releases. To assess program success, we genotyped 304 hair samples, subsampled from the known range in 2000 and 2001, and 2005 and 2006, at 7 microsatellite loci. We compared diversity, effective population size, and genetic connectivity over time in each population. Diversity remained stable over time and there was evidence of increasing effective population size. We determined population structure in both periods after correcting for differences in sample sizes. The geographic distribution of these populations roughly corresponded with the original release locations, which suggests the release sites had residual effects on the population structure. However, given that both reintroduction sites had similar source populations, habitat fragmentation, due to cropland, may be associated with the population structure we found. Although our results indicate growing, stable populations, future connectivity analyses are warranted to ensure both populations are not subject to negative small‐population effects. Our results demonstrate the importance of multiple sampling years to fully capture population dynamics of reintroduced populations. Análisis Temporal de la Estructura Genética para Evaluar la Dinámica Poblacional de Zorros (Vulpes velox) Reintroducidos 相似文献
193.
Veronica M. Bueno Kevin R. Burgio Carrie A. Cizauskas Christopher F. Clements Dana P. Seidel Nyeema C. Harris 《Conservation biology》2016,30(4):724-733
Parasitic species, which depend directly on host species for their survival, represent a major regulatory force in ecosystems and a significant component of Earth's biodiversity. Yet the negative impacts of parasites observed at the host level have motivated a conservation paradigm of eradication, moving us farther from attainment of taxonomically unbiased conservation goals. Despite a growing body of literature highlighting the importance of parasite‐inclusive conservation, most parasite species remain understudied, underfunded, and underappreciated. We argue the protection of parasitic biodiversity requires a paradigm shift in the perception and valuation of their role as consumer species, similar to that of apex predators in the mid‐20th century. Beyond recognizing parasites as vital trophic regulators, existing tools available to conservation practitioners should explicitly account for the unique threats facing dependent species. We built upon concepts from epidemiology and economics (e.g., host‐density threshold and cost‐benefit analysis) to devise novel metrics of margin of error and minimum investment for parasite conservation. We define margin of error as the risk of accidental host extinction from misestimating equilibrium population sizes and predicted oscillations, while minimum investment represents the cost associated with conserving the additional hosts required to maintain viable parasite populations. This framework will aid in the identification of readily conserved parasites that present minimal health risks. To establish parasite conservation, we propose an extension of population viability analysis for host–parasite assemblages to assess extinction risk. In the direst cases, ex situ breeding programs for parasites should be evaluated to maximize success without undermining host protection. Though parasitic species pose a considerable conservation challenge, adaptations to conservation tools will help protect parasite biodiversity in the face of an uncertain environmental future. 相似文献
194.
本文根据采自嘉陵江合川江段的483尾标本,研究吻(鱼句)的生长和繁殖力,并对其资源的增殖保护和合理利用提出初步意见。 相似文献
195.
Effects of landfill gas on subtropical woody plants 总被引:2,自引:0,他引:2
An account is given of the influence of landfill gas on tree growth in the field at Gin Drinkers' Bay (GDB) landfill, Hong
Kong, and in the laboratory. Ten species (Acacia confusa, Albizzia lebbek, Aporusa chinensis, Bombax malabaricum, Castanopsis fissa, Liquidambar formosana, Litsea glutinosa,
Machilus breviflora, Pinus elliottii, andTristania conferta), belonging to eight families, were transplanted to two sites, one with a high concentration of landfill gas in the cover
soil (high-gas site, HGS) and the other with a relatively low concentration of gas (low-gas site, LGS). Apart from the gaseous
composition, the general soil properties were similar. A strong negative correlation between tree growth and landfill gas
concentration was observed. A laboratory study using the simulated landfill gas to fumigate seedlings of the above species
showed that the adventitious root growth ofAporusa chinensis, Bombax malabaricum, Machilus breviflora, andTristania confera was stimulated by the gas, with shallow root systems being induced.Acacia confusa, Albizzia lebbek, andLitsea glutinosa were gas-tolerant, while root growth ofCastanopsis fissa, Liquidambar formosana, andPinus elliottii was inhibited. In most cases, shoot growth was not affected, exceptions beingBombax malabaricum, Liquidambar formosana, andTristania conferta, where stunted growth and/or reduced foliation was observed.
A very high CO2 concentration in cover soil limits the depth of the root system. Trees with a shallow root system become very susceptible
to water stress. The effects of low O2 concentration in soil are less important than the effects of high CO2 concentration.Acacia confusa, Albizzia lebbek, andTristania conferta are suited for growth on subtropical completed landfills mainly due to their gas tolerance and/or drought tolerance. 相似文献
196.
Dr Abdal‐Majeed I. Daghistani BA MSc PhD MRTPI 《Journal of Environmental Planning and Management》1991,34(1):2-9
The towns and cities of Saudi Arabia have been subjected to sustained growth pressures since the transformation of the country's economy following the discovery of oil in the Eastern Province of the Kingdom. The rapid growth which has been experienced has created major problems for the central and local government agencies responsible for planning and managing urban growth. The experience of Jeddah, one of the major cities in Saudi Arabia, is described and the problems of planning and managing its growth are analysed. Weaknesses relating to the structure of the planning system are identified, as are major difficulties in relation to the quality and quantity of professional staff. Recent attempts to improve the operation of the planning system are described and evaluated. 相似文献
197.
198.
Climatic and stream-flow controls on tree growth in a Western montane riparian forest 总被引:2,自引:0,他引:2
Humans have severely impacted riparian ecosystems through water diversions, impoundments, and consumptive uses. Effective
management of these important areas is becoming an increasingly high priority of land managers, particularly as municipal,
industrial, and recreational demands for water increase. We examined radial tree growth of four riparian tree species (Pinus jeffreyi, Populus trichocarpa, Betula occidentalis, and Pinus monophylla) along Bishop Creek, California, and developed models relating basal area increment (BAI) and relative basal area increment
(RBAI) to climatic and stream flow variables. Between years 1995–1999, univariate regression analysis with stream flow explained
29 to 61% of the variation in BAI and RBAI among all species except P. trichocarpa; growth by P. trichocarpa was not significantly related to stream flows over this period. Stepwise linear regression indicated that species responded
differently to climatic variables, and models based on these variables explained between 33 to 86% of variation in BAI and
RBAI during the decade of the 1990s. We examined branch growth of P. trichocarpa for sensitivity to differences in stream flow regimes and found that annual branch growth did not vary between a high- and
low-flow site, but that annual branch growth was significantly higher in wet years with greater stream flows. Our results
support the establishment of site-specific management goals by land managers that take into account all of the important tree
species present in riparian ecosystems and their differential responses to altered hydrologic condition. Instream flow requirements
for maintaining tree growth and vigor are only one of the species-specific responses that need to be evaluated, and these
assessments should attempt to separate experimentally stream-flow (managed) controls from climatic (unmanaged) controls on
growth. 相似文献
199.
200.
关于环境保护的可持续发展 总被引:2,自引:0,他引:2
阐述了可持续性发展的定义和内涵,介绍了可持续性发展概念产生的历史背景和该概念不断完善和补充的过程。并论述了经济增长、环境保护与可持续性发展的关系,最后,提出了实施可持续发展战略应注意的一些问题。 相似文献