全文获取类型
收费全文 | 10439篇 |
免费 | 8篇 |
国内免费 | 15篇 |
专业分类
安全科学 | 27篇 |
废物处理 | 814篇 |
环保管理 | 1291篇 |
综合类 | 1060篇 |
基础理论 | 3289篇 |
环境理论 | 2篇 |
污染及防治 | 1980篇 |
评价与监测 | 1053篇 |
社会与环境 | 944篇 |
灾害及防治 | 2篇 |
出版年
2023年 | 2篇 |
2022年 | 15篇 |
2021年 | 17篇 |
2020年 | 8篇 |
2019年 | 9篇 |
2018年 | 1486篇 |
2017年 | 1390篇 |
2016年 | 1210篇 |
2015年 | 151篇 |
2014年 | 42篇 |
2013年 | 98篇 |
2012年 | 502篇 |
2011年 | 1399篇 |
2010年 | 736篇 |
2009年 | 646篇 |
2008年 | 932篇 |
2007年 | 1270篇 |
2006年 | 48篇 |
2005年 | 49篇 |
2004年 | 61篇 |
2003年 | 92篇 |
2002年 | 116篇 |
2001年 | 22篇 |
2000年 | 16篇 |
1999年 | 8篇 |
1998年 | 17篇 |
1997年 | 9篇 |
1996年 | 4篇 |
1995年 | 12篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1987年 | 2篇 |
1984年 | 12篇 |
1983年 | 8篇 |
1981年 | 3篇 |
1965年 | 7篇 |
1964年 | 3篇 |
1963年 | 4篇 |
1962年 | 9篇 |
1961年 | 11篇 |
1958年 | 2篇 |
1954年 | 1篇 |
1947年 | 1篇 |
1942年 | 1篇 |
1941年 | 2篇 |
1938年 | 1篇 |
1935年 | 2篇 |
1932年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
991.
We quantified horizontal transport patterns and the net exchange of nutrients between shallow regions and the open sea in the Baltic proper. A coupled biogeochemical-physical circulation model was used for transient simulations 1961-2100. The model was driven by regional downscaling of the IPCC climate change scenario A1B from two global General Circulation Models in combination with two nutrient load scenarios. Modeled nutrient transports followed mainly the large-scale internal water circulation and showed only small circulation changes in the future projections. The internal nutrient cycling and exchanges between shallow and deeper waters became intensified, and the internal removal of phosphorus became weaker in the warmer future climate. These effects counteracted the impact from nutrient load reductions according to the Baltic Sea Action Plan. The net effect of climate change and nutrient reductions was an increased net import of dissolved inorganic phosphorus to shallow areas in the Baltic proper. 相似文献
992.
Trees are taller than shrubs, grasses, and herbs. What is the disadvantage of being tall so that trees are restricted to warmer regions than low stature life forms? This article offers a brief review of the current state of biological treeline theory, and then explores the significance of tallness from a carbon balance, freezing resistance, and microclimatological perspective. It will be argued that having of a woody stem is neither a burden to the carbon balance nor does it add to the risk of freezing damage. The physiological means of trees to thrive in cold climates are similar to small stature plants, but due to their size, and, thus, closer aerodynamic coupling to air circulation, trees experience critically low temperatures at lower elevation and latitude than smaller plants. Hence, trees reach a limit at treeline for physical reasons related to their stature. 相似文献
993.
We report observations of disappearance of Erica tetralix in wet heathland, which is unlikely to be caused by competition, as E. tetralix is dying before its place is taken up by other species. To investigate the causes, we used both old and new data. Results showed that presence of Molinia caerulea and Calluna vulgaris were substantial in the former E. tetralix dominated areas. Measurements of the C/N ratio in the morlayer were between 21 and 26 under the E. tetralix stands. As the expected C/N ratio in a healthy nutrient poor ecosystem like the E. tetralix wet heathland is around 30, this indicates that the ratio is probably decreasing and, correspondingly, the probability of nitrogen leaching from the ecosystem is increasing. The morlayer pH was extremely low—between 3.03 and 3.78. This represents a pH decline since the 1960s, where pH values generally were above 4. This supports the hypothesis that the decrease in morlayer pH is the major factor explaining the disappearance of E. tetralix and that measures to increase pH should be considered as part of the recommendations for relevant future management.
Electronic supplementary material
The online version of this article (doi:10.1007/s13280-012-0251-z) contains supplementary material, which is available to authorized users. 相似文献994.
995.
Primary production in the eutrophic Baltic Sea is limited by nitrogen availability; hence denitrification (natural transformation
of nitrate to gaseous N2) in the sediments is crucial in mitigating the effects of eutrophication. This study shows that dissimilatory nitrate reduction
to ammonium (DNRA) process, where nitrogen is not removed but instead recycled in the system, dominates nitrate reduction
in low oxygen conditions (O2 <110 μM), which have been persistent in the central Gulf of Finland during the past decade. The nitrogen removal rates measured
in this study show that nitrogen removal has decreased in the Gulf of Finland compared to rates measured in mid-1990s and
the decrease is most likely caused by the increased bottom water hypoxia. 相似文献
996.
Interacting forces of climate change and globalization are transforming the Arctic. Triggered by a non-linear shift in sea
ice, this transformation has unleashed mounting interest in opportunities to exploit the region’s natural resources as well
as growing concern about environmental, economic, and political issues associated with such efforts. This article addresses
the implications of this transformation for governance, identifies limitations of existing arrangements, and explores changes
needed to meet new demands. It advocates the development of an Arctic regime complex featuring flexibility across issues and
adaptability over time along with an enhanced role for the Arctic Council both in conducting policy-relevant assessments and
in promoting synergy in interactions among the elements of the emerging Arctic regime complex. The emphasis throughout is
on maximizing the fit between the socioecological features of the Arctic and the character of the governance arrangements
needed to steer the Arctic toward a sustainable future. 相似文献
997.
998.
Global climate issues and a looming energy crisis put agriculture under pressure in Sub-Saharan Africa. Climate adaptation measures must entail sustainable development benefits, and growing crops for food as well as energy may be a solution, removing people from hunger and poverty without compromising the environment. The present study investigated the feasibility of using non-food parts of cassava for energy production and the promising results revealed that at least 28% of peels and stems comprise dry matter, and 10 g feedstock yields >8.5 g sugar, which in turn produced >60% ethanol, with pH ≈ 2.85, 74-84% light transmittance and a conductivity of 368 mV, indicating a potential use of cassava feedstock for ethanol production. Thus, harnessing cassava for food as well as ethanol production is deemed feasible. Such a system would, however, require supportive policies to acquire a balance between food security and fuel. 相似文献
999.
Yutaka Tamaura 《Ambio》2012,41(2):108-111
When a concentrated solar beam is irradiated to the ceramics such as Ni-ferrite, the high-energy flux in the range of 1500–2500 kW/m2 is absorbed by an excess Frenkel defect formation. This non-equilibrium state defect is generated not by heating at a low heating-rate (30 K/min), but by irradiating high flux energy of concentrated solar beam rapidly at a high heating rate (200 K/min). The defect can be spontaneously converted to chemical energy of a cation-excess spinel structure (reduced-oxide form) at the temperature around 1773 K. Thus, the O2 releasing reaction (α-O2 releasing reaction) proceeds in two-steps; (1) high flux energy of concentrated solar beam absorption by formation of the non-equilibrium Frenkel defect and (2) the O2 gas formation from the O2? in the Frenkel defect even in air atmosphere. The 2nd step proceeds without the solar radiation. We may say that the 1st step is light reaction, and 2nd step, dark reaction, just like in photosynthesis process. 相似文献
1000.
The photovoltaic conversion efficiency for near-infrared (NIR) sunlight is improved successfully by dye sensitization of bulk heterojunction polymer solar cells, in which the active layer was prepared by a ternary blend of poly(3-hexylthiophene), a fullerene derivative (1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-methanofullerene), and an NIR dye, silicon phthalocyanine bis(trihexylsilyl oxide). The mechanism of the NIR-dye sensitization is studied by femtosecond transient absorption spectroscopy. 相似文献