全文获取类型
收费全文 | 10432篇 |
免费 | 51篇 |
国内免费 | 140篇 |
专业分类
安全科学 | 42篇 |
废物处理 | 804篇 |
环保管理 | 1277篇 |
综合类 | 1246篇 |
基础理论 | 3280篇 |
环境理论 | 1篇 |
污染及防治 | 1942篇 |
评价与监测 | 1057篇 |
社会与环境 | 951篇 |
灾害及防治 | 23篇 |
出版年
2024年 | 3篇 |
2023年 | 16篇 |
2022年 | 57篇 |
2021年 | 35篇 |
2020年 | 45篇 |
2019年 | 38篇 |
2018年 | 1497篇 |
2017年 | 1404篇 |
2016年 | 1246篇 |
2015年 | 163篇 |
2014年 | 83篇 |
2013年 | 70篇 |
2012年 | 514篇 |
2011年 | 1401篇 |
2010年 | 725篇 |
2009年 | 647篇 |
2008年 | 922篇 |
2007年 | 1261篇 |
2006年 | 31篇 |
2005年 | 48篇 |
2004年 | 50篇 |
2003年 | 79篇 |
2002年 | 118篇 |
2001年 | 32篇 |
2000年 | 28篇 |
1999年 | 9篇 |
1998年 | 13篇 |
1997年 | 1篇 |
1996年 | 5篇 |
1995年 | 5篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1935年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
941.
With 207 million ha of forest covering 22% of its land area, China ranks fifth in the world in forest area. Rapid economic
growth, climate change, and forest disturbances pose new, complex challenges for forest research and management. Progress
in meeting these challenges is relevant beyond China, because China’s forests represent 34% of Asia’s forests and 5% of the
worlds’ forests. To provide a broader understanding of these management challenges and of research and policies that address
them, we organized this special issue on contemporary forest research and management issues in China. At the national level,
papers review major forest types and the evolution of sustainable forestry, the development of China’s forest-certification
efforts, the establishment of a forest inventory system, and achievements and challenges in insect pest control in China.
Papers focused on Northern China address historical, social, and political factors that have shaped the region’s forests;
the use of forest landscape models to assess how forest management can achieve multiple objectives; and analysis and modeling
of fuels and fire behavior. Papers addressing Central and South China describe the “Grain for Green” program, which converts
low productivity cropland to grassland and woodland to address erosion and soil carbon sequestration; the potential effects
of climate change on CO2 efflux and soil respiration; and relationships between climate and net primary productivity. China shares many forest management
and research issues with other countries, but in other cases China’s capacity to respond to forest management challenges is
unique and bears watching by the rest of the world. 相似文献
942.
Pasqualini V Oberti P Vigetta S Riffard O Panaïotis C Cannac M Ferrat L 《Environmental management》2011,48(1):38-56
Forest management can benefit from decision support tools, including GIS-based multicriteria decision-aiding approach. In
the Mediterranean region, Pinus pinaster forests play a very important role in biodiversity conservation and offer many socioeconomic benefits. However, the conservation
of this species is affected by the increase in forest fires and the expansion of Matsucoccus feytaudi. This paper proposes a methodology based on commonly available data for assessing the values and risks of P. pinaster forests and to generating maps to aid in decisions pertaining to fire and phytosanitary risk management. The criteria for
assessing the values (land cover type, legislative tools for biodiversity conservation, environmental tourist sites and access
routes, and timber yield) and the risks (fire and phytosanitation) of P. pinaster forests were obtained directly or by considering specific indicators, and they were subsequently aggregated by means of GIS-based
multicriteria analysis. This approach was tested on the island of Corsica (France), and maps to aid in decisions pertaining
to fire risk and phytosanitary risk (M. feytaudi) were obtained for P. pinaster forest management. Study results are used by the technical offices of the local administration—Corsican Agricultural and Rural Development Agency (ODARC)—for planning the conservation of P. pinaster forests with regard to fire prevention and safety and phytosanitary risks. The decision maker took part in the evaluation
criteria study (weight, normalization, and classification of the values). Most suitable locations are given to target the
public intervention. The methodology presented in this paper could be applied to other species and in other Mediterranean
regions. 相似文献
943.
Forests are a major terrestrial ecosystem providing multiple ecosystem services. However, the importance of forests is frequently
underestimated from an economic perspective because of the externalities and public good properties of these services. Forest
eco-compensation is a transfer mechanism that serves to internalize the externalities of forest ecosystem services by compensating
individuals or companies for the losses or costs resulting from the provision of these services. China’s current forest eco-compensation
system is centered mainly on noncommercial forest. The primary measures associated with ecosystem services are (1) a charge
on destructive activities, such as indiscriminate logging, and (2) compensation for individual or local activities and investments
in forest conservation. The Compensation Fund System for Forest Ecological Benefits was first listed in the Forest Law of the People’s Republic of China in 1998. In 2004, the Central Government Financial Compensation Fund, an important source for the Compensation Fund for Forest
Ecological Benefits, was formally established. To improve the forest eco-compensation system, it is crucial to design and
establish compensation criteria for noncommercial forests. These criteria should take both theoretical and practical concerns
into account, and they should be based on the quantitative valuation of ecosystem services. Although some initial headway
has been made on this task, the implementation of an effective forest eco-compensation system in China still has deficiencies
and still faces problems. Implementing classification-based and dynamic management for key noncommercial forests and establishing
an eco-compensation mechanism with multiple funding sources in the market economy are the key measures needed to conquer these
problems and improve the forest eco-compensation system and China’s forestry development in sequence. 相似文献
944.
Rita JC Gama-Rodrigues EF Gama-Rodrigues AC Polidoro JC Machado RC Baligar VC 《Environmental management》2011,48(1):134-141
Agroforestry systems (AFSs) have an important role in capturing above and below ground soil carbon and play a dominant role
in mitigation of atmospheric CO2. Attempts has been made here to identify soil organic matter fractions in the cacao-AFSs that have different susceptibility
to microbial decomposition and further represent the basis of understanding soil C dynamics. The objective of this study was
to characterize the organic matter density fractions and soil size fractions in soils of two types of cacao agroforestry systems
and to compare with an adjacent natural forest in Bahia, Brazil. The land-use systems studied were: (1) a 30-year-old stand
of natural forest with cacao (cacao cabruca), (2) a 30-year-old stand of cacao with Erythrina glauca as shade trees (cacao + erythrina), and (3) an adjacent natural forest without cacao. Soil samples were collected from 0-10 cm
depth layer in reddish-yellow Oxisols. Soil samples was separated by wet sieving into five fraction-size classes (>2000 μm,
1000–2000 μm, 250–1000 μm, 53–250 μm, and <53 μm). C and N accumulated in to the light (free- and intra-aggregate density
fractions) and heavy fractions of whole soil and soil size fraction were determined. Soil size fraction obtained in cacao
AFS soils consisted mainly (65 %) of mega-aggregates (>2000 μm) mixed with macroaggregates (32–34%), and microaggregates (1–1.3%).
Soil organic carbon (SOC) and total N content increased with increasing soil size fraction in all land-use systems. Organic
C-to-total N ratio was higher in the macroaggregate than in the microaggregate. In general, in natural forest and cacao cabruca
the contribution of C and N in the light and heavy fractions was similar. However, in cacao + erythrina the heavy fraction
was the most common and contributed 67% of C and 63% of N. Finding of this study shows that the majority of C and N in all
three systems studied are found in macroaggregates, particularly in the 250–1000 μm size aggregate class. The heavy fraction
was the most common organic matter fraction in these soils. Thus, in mature cacao AFS on highly weathered soils the main mechanisms
of C stabilization could be the physical protection within macroaggregate structures thereby minimizing the impact of conversion
of forest to cacao AFS. 相似文献
945.
Increasingly government agencies are seeking to quantify the outcomes of proposed policy options in terms of ecosystem service
benefits, yet conflicting definitions and ad hoc approaches to measuring ecosystem services have created confusion regarding
how to rigorously link ecological change to changes in human well-being. Here, we describe a step-by-step framework for producing
ecological models and metrics that can effectively serve an economic-benefits assessment of a proposed change in policy or
management. A focus of the framework is developing comparable units of ecosystem goods and services to support decision-making,
even if outcomes cannot be monetized. Because the challenges to translating ecological changes to outcomes appropriate for
economic analyses are many, we discuss examples that demonstrate practical methods and approaches to overcoming data limitations.
The numerous difficult decisions that government agencies must make to fairly use and allocate natural resources provides
ample opportunity for interdisciplinary teams of natural and social scientists to improve methods for quantifying changes
in ecosystem services and their effects on human well-being. This framework is offered with the intent of promoting the success
of such teams as they support managers in evaluating the equivalency of ecosystem service offsets and trades, establishing
restoration and preservation priorities, and more generally, in developing environmental policy that effectively balances
multiple perspectives. 相似文献
946.
Generalized additive models were used to synthesize the data from 52 publications on the gonad growth and spawning seasonality
of Paracentrotus lividus and identify spatial and temporal patterns in the reproductive processes. According to our results, Atlantic populations
spawn in spring and develop large gonads (6.4 ± 0.2% of fresh body weight (mean ± SE)), which increase in size toward higher
latitudes. While in the Mediterranean, the gonads are smaller (3.1 ± 0.1%), possibly as the result of successive spawnings
which impede nutrients accumulating in the gonads. Differences were also observed between habitats: gonad production was higher
in seagrass meadows in the Mediterranean and in subtidal rocky substrates in the Atlantic. Food availability might cause these
variations as well as the negative correlation observed between depth and the gonad index for rocky substrates. Sex and body
size do not seem to influence greatly gonad growth. 相似文献
947.
Carey E. Kuhn 《Marine Biology》2011,158(3):649-663
In the heterogeneous marine environment, predators can increase foraging success by targeting physical oceanographic features,
which often aggregate prey. For northern fur seals (Callorhinus ursinus), two prevalent oceanographic features characterize foraging areas during summer in the Bering Sea: a stable thermocline
and a subsurface “cold pool”. The objective of this study was to examine the influence of these features on foraging behavior
by equipping fur seals from St. Paul Island (Alaska, USA) with time-depth recorders that also measured water temperature.
Foraging bout variables (e.g., mean dive depth and percent time diving in a bout) were compared with respect to subsurface
thermal characteristics (thermocline presence and strength and cold pool presence). Over 74% of bouts occurred in association
with strong thermoclines (temperature change > 5°C). Few differences were found for dive behavior in relation to the presence
of a thermocline and the cold pool, but for epipelagic bouts, a strong thermocline resulted in increased bottom times, number
of dive wiggles, and percent time diving when compared to moderate thermoclines. There was also a positive relationship between
mean dive depth and thermocline depth. The combination of increasing foraging effort in areas with strong thermoclines and
diving to depths closely related to the thermocline indicates this feature is important foraging habitat for northern fur
seals and may act to concentrate prey and increase foraging success. By recognizing the environmental features northern fur
seals use to find prey, managers will be better equipped to identify and protect foraging habitat that is important to northern
fur seals, and possibly other marine predators in the Bering Sea. 相似文献
948.
Claudia Hollatz Leonardo Flach C. Scott Baker Fabrício R. Santos 《Marine Biology》2011,158(4):927-933
A large macrogeographic differentiation has been observed among Sotalia guianensis populations along the South American coast. However, no genetic structure has been detected so far in closely distributed
populations of this species, even though it has been observed in other cetaceans. Here, we examined the fine scale population
structure for the largest populations of S. guianensis inhabiting Sepetiba and Paraty embayments at the south-eastern coast of Rio de Janeiro, Brazil. Analysis of mitochondrial
DNA (mtDNA) control region sequences failed to detect variability among sequences. Conversely, evidence of significant male
population structure was found on the basis of ten nuclear microsatellite loci. Surprisingly, the microsatellite markers were
able to distinguish between individuals from the two embayments located 60 km apart. The results suggest that differences
in habitat type and behavioral specializations are likely to explain the patterns of genetic structure. These findings should
provide baselines for the management of communities exposed to increasing human-driven habitat loss. 相似文献
949.
The Maltese top-shell, Gibbula nivosa Adams 1851, is a critically endangered marine trochid gastropod endemic to the Maltese Islands (central Mediterranean). Previously unrecorded
live since 1981, rediscovery of this species in 2006 has enabled the collection of basic biological data for the first time,
based on a population in Sliema Creek. The field distribution and habitat preferences of G. nivosa were investigated via stratified random sampling, while aspects of its behaviour were studied through laboratory experiments.
Gibbula nivosa occurred primarily in near-homogeneous or homogeneous infralittoral cobble/pebble beds, at an overall density of 17.6 ± 25.0 SD individuals m−2; however, large spatial and temporal variations in abundance were recorded. The snails did not exhibit gregarious behaviour
and the slightly clumped dispersion pattern noted in the field appeared to result from patchiness of the habitat. Recruitment
was observed in post-summer months, which, together with data on shell-size distributions, suggests that G. nivosa spawns in early summer and attains adult size (maximum shell width ~9 mm) in less than 1 year. Gibbula nivosa showed a circadian activity pattern with nocturnal foraging involving indiscriminate ingestion of particles browsed off the
substratum; observations on responses to four potential predators suggest that nocturnal activity may have evolved in response
to diurnal predation. Historical records of snail occurrence and the present study suggest that population declines of G. nivosa in the past were probably related to habitat alteration as a result of anthropogenic pressure. 相似文献
950.
The habitat experienced during early life-history stages can determine the number and quality of individuals that recruit
to adult populations. In a field experiment, biogenic habitat complexity was manipulated (presence or absence of foliose macroalgae)
at two depths (2–3 m and 5–6 m) and the habitat-dependent effects on recruitment of the black foot abalone (Haliotis iris) were examined at three field sites along the south coast of Wellington, New Zealand (41°20′S, 174°47′E), between July and
November 2005. Recruit density (<5 weeks post-settlement) was measured on cobbles covered with crustose coralline algae. Habitats
of low complexity (barrens treatments) had consistently greater densities of recruits than habitats of high complexity (algae
treatments). However, recruits in algae habitats were larger, and for deep habitats, there was greater survival in algae habitats
compared with barrens habitats. While depth had no significant effect on early recruit (<2 weeks post-settlement) density,
late recruit (<5 weeks post-settlement) density was greater in shallow habitats, and so it seems recruit survival was greater
in shallow habitats. In this experiment, algal habitat complexity had strong effects on early recruit abundance, but habitat-dependent
variations in recruit growth and survival may modify initial patterns of abundance and determine recruitment to adult abalone
populations. 相似文献