全文获取类型
收费全文 | 267篇 |
免费 | 38篇 |
国内免费 | 22篇 |
出版年
2023年 | 12篇 |
2022年 | 10篇 |
2021年 | 19篇 |
2020年 | 6篇 |
2019年 | 16篇 |
2018年 | 11篇 |
2017年 | 15篇 |
2016年 | 10篇 |
2015年 | 15篇 |
2014年 | 12篇 |
2013年 | 21篇 |
2012年 | 13篇 |
2011年 | 14篇 |
2010年 | 16篇 |
2009年 | 13篇 |
2008年 | 10篇 |
2007年 | 12篇 |
2006年 | 7篇 |
2005年 | 14篇 |
2004年 | 4篇 |
2003年 | 7篇 |
2002年 | 3篇 |
2001年 | 9篇 |
2000年 | 6篇 |
1999年 | 6篇 |
1998年 | 7篇 |
1997年 | 1篇 |
1996年 | 12篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有327条查询结果,搜索用时 968 毫秒
241.
The rising prominence of life cycle assessment (LCA) and similar environmental accounting frameworks reflects increasing awareness of the pressing necessity of managing both for eco‐efficiency and with respect to the macroscale, environmental dimensions of the material/energy flows and emissions that underpin all economic activity. However, by relying on environmentally myopic market signals to inform evaluations of the biophysical dimensions of economic activity through the widespread use of market information (in particular, via economic allocation) in LCA, we are concerned that researchers greatly compromise the value of their work to furthering these objectives. In response to this problem, we provide a systematic critique of the use of market information in attributional LCA and present the case for an ecological‐economic approach to the execution, interpretation, and application of biophysically consistent LCA research specifically intended to elucidate the environmental dimensions of meeting human needs. We further argue that, although LCA has historically been limited to informing eco‐efficiency considerations, it can and should also be used to manage for sustainable scale, which is the first condition of sustainability. 相似文献
242.
243.
It is the economy,stupid! Projecting the fate of fish populations using ecological–economic modeling
下载免费PDF全文
![点击此处可从《Global Change Biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Martin F. Quaas Thorsten B. H. Reusch Jörn O. Schmidt Olli Tahvonen Rudi Voss 《Global Change Biology》2016,22(1):264-270
Four marine fish species are among the most important on the world market: cod, salmon, tuna, and sea bass. While the supply of North American and European markets for two of these species – Atlantic salmon and European sea bass – mainly comes from fish farming, Atlantic cod and tunas are mainly caught from wild stocks. We address the question what will be the status of these wild stocks in the midterm future, in the year 2048, to be specific. Whereas the effects of climate change and ecological driving forces on fish stocks have already gained much attention, our prime interest is in studying the effects of changing economic drivers, as well as the impact of variable management effectiveness. Using a process‐based ecological–economic multispecies optimization model, we assess the future stock status under different scenarios of change. We simulate (i) technological progress in fishing, (ii) increasing demand for fish, and (iii) increasing supply of farmed fish, as well as the interplay of these driving forces under different scenarios of (limited) fishery management effectiveness. We find that economic change has a substantial effect on fish populations. Increasing aquaculture production can dampen the fishing pressure on wild stocks, but this effect is likely to be overwhelmed by increasing demand and technological progress, both increasing fishing pressure. The only solution to avoid collapse of the majority of stocks is institutional change to improve management effectiveness significantly above the current state. We conclude that full recognition of economic drivers of change will be needed to successfully develop an integrated ecosystem management and to sustain the wild fish stocks until 2048 and beyond. 相似文献
244.
245.
《Current biology : CB》2019,29(12):2043-2050.e8
- Download : Download high-res image (290KB)
- Download : Download full-size image
246.
Yoshihiko Sakanishi Hiromi Kasai Koichiro Enomoto Masashi Toda Jiro Tanaka 《Phycological Research》2019,67(4):253-260
Trade‐offs are considered key to understanding mechanisms supporting the coexistence of multiple plant species. Thus, understanding the mechanisms underlying trade‐offs is expected to contribute to conservation and management of macroalgal beds composed of diverse macroalgae of rocky shore ecosystems. To test the occurrence of trade‐offs between productivity and thallus toughness as well as pair‐wise thallus trait relationships that are expected to indirectly relate to any trade‐offs, traits and relationships for 13 species of macroalgae from the central area along the Japan Sea coast of Honshu, Japan were examined. In each species we examined for photosynthetic capacity per unit biomass (as Amass) and nitrogen (i.e., photosynthetic nitrogen‐use efficiency, PNUE), nitrogen content (as Nmass), thallus mass per unit thallus area (as TMA) and force required to penetrate the thallus (as Fp, a common index of leaf toughness in land plants by punch test). A significant negative correlation indicating a trade‐off between productivity and thallus toughness was found between Amass or PNUE and Fp. Pair‐wise relationships that were expected to indirectly relate to the trade‐off were as follows. Amass was positively correlated with Nmass. Thalli with high Nmass extensively utilizing nitrogen in the photosynthetic parts, and consequently exhibiting elevated metabolic rates. Moreover, thalli with high Nmass tended to be associated with low TMA, and Nmass decreased with increasing TMA. A significant negative correlation was observed between TMA and Amass or PNUE because of the linkage of high Amass or PNUE with high Nmass and high Nmass associated with low TMA, while a significant positive correlation was observed between TMA and Fp. The two correlations indicate a physiological and structural trade‐off, which underlies the interdependency of thallus traits. Results of multivariate analyses also indicated that the thallus traits interdependently vary across a single axis based on the trade‐off. 相似文献
247.
D. E. Turney M. Ansari D. V. Kalaga R. Yakobov S. Banerjee J. B. Joshi 《Biotechnology progress》2019,35(1):e2710
Bioreactors are of interest for gas-to-liquid conversion of stranded or waste industrial gases, such as CO, CH4, or syngas. Process economics requires reduction of bioreactor cost and size while maintaining intense production via rapid delivery of gases to the liquid phase (i.e., high kLa). Here, we show a novel bioreactor design that outperforms all known technology in terms of gas transfer energy efficiency (kLa per power density) while operating at high kLa (i.e., near 0.8 s−1). The reactor design uses a micro-jet array to break feedstock gas into a downward microbubble flow. Hydrodynamic and surfactant measurements show the reactor's advanced performance arises from its bubble breakage mechanism, which limits fluid shear to a thin plane located at an optimal location for bubble breakage. Power dissipation and kL are shown to scale with micro-jet diameter rather than reactor diameter, and the micro-jet array achieves improved performance compared to classical impinging-jets, ejector, or U-loop reactors. The hydrodynamic mechanism by which the micro-jets break bubbles apart is shown to be shearing the bubbles into filaments then fragmentation by surface tension rather than “cutting in half” of bubbles. Guided by these hydrodynamic insights, strategies for industrial design are given. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2710, 2019 相似文献
248.
Costs and benefits of cervical screening. I. The costs of the cervical screening programme 总被引:1,自引:0,他引:1
In 1991, the average total Health Service cost of a cervical smear, including follow up at the colposcopy clinic, was almost £22.70 in the Perth and Kinross district of Scotland. The average cost per colposcopy clinic visit was £30. The main cost elements were in general practice (55% of total) and the laboratory (33%), and most of the cost was for staff time. 相似文献
249.
Jørgen Dan Petersen Nanna Rask Harley Bundgaard Madsen Ole Tyrsted Jørgensen Stig Eggert Petersen Susanne V. Koch Nielsen Cathrine Bøgh Pedersen Mikael Hjorth Jensen 《Hydrobiologia》2009,629(1):71-89
Implementation of the EU Water Framework Directive (WFD) is a huge environmental management challenge for Europe, demanding an integrated sustainable approach to water management and a common objective of obtaining ‘good status’ for all water bodies before 2015. The main task is the preparation of a river basin management plan for each of the 96 European river basin districts before the end of 2009. In Odense River Basin (island of Fyn, Denmark), one of 14 appointed European Pilot River Basins, the implementation of the WFD has been developed and tested in practice. Reference conditions and ecological status classification for Odense Fjord, based on eelgrass (Zostera marina) depth limit and nutrient concentrations, have been drawn up through a combination of historical data and modelling tools. A subsequent quantitative linking of pressures and impact, in casu between land-based nitrogen (N) loading of the fjord and resulting nutrient concentrations and eelgrass appearance, provided an estimate of the needed nitrogen load reduction of the fjord. This amounted to approx. 1,200 tonnes N per year (an annual load reduction of ca. 11 kg N ha?1 of catchment area or ca. 19.5 g N m?2 of fjord surface)—a load reduction of ca. 60% from the present level—to obtain at least ‘good’ ecological status sensu WFD. It is presently not possible to quantify a target load for phosphorus (P) in relation to marine environmental objectives. An economically feasible programme of measures to obtain ‘good’ status in all surface water and groundwater bodies in Odense River Basin, using an integrated cost-effectiveness analysis, showed that re-establishment of wetlands, catchcrops, and reduced fertilisation norms are the most effective measures if large reductions in N loads to the aquatic environment are to be achieved. The total socio-economic cost of implementing the WFD in the river basin amounts to about 13 million €/year, which will increase the expense for water services by only 0.5–0.6% of the total income and production value in the basin (15,650 million €/year). Investments to obtain the needed nitrogen load reductions from agriculture are thus economically feasible. Further, it is not an impossible task, either economically or technically, to reach the objectives of the WFD while still retaining the possibility of keeping a high agricultural production in the catchment (maintaining livestock production but decreasing crop production in the case of Odense River Basin). The future conditions in Odense Fjord will not only depend on the success in reducing the load from the river basin area, but will also be affected by the trend in the nutrient loss from the whole Baltic catchment area. The high growth rates in the new EU Member States thus pose an important challenge to water managers, and decoupling of economic growth from pressure on water bodies will be necessary. Finally, a number of challenges facing water managers around the Baltic and within the EU, namely preconditions required to successfully implement the WFD, are presented. 相似文献
250.
1. Thirgood & Redpath (2008) propose ways in which red grouse : hen harrier conflicts could be resolved. It has also been suggested that grouse management could accept lower bag sizes (number of birds shot) thus reducing the need for intensive management of predators and habitats. This would allow hen harriers to co-exist more easily on grouse moors.
2. We compare the bags, costs and incomes from these less intensive forms of grouse shooting with the more intensive driven shooting.
3. Allowing high density grouse moors to decline to low density ones will result in greater loss of income than the corresponding saving of costs. This can result in moor owners abandoning grouse management and thus gamekeepers losing their employment.
4. Losing gamekeepers from the uplands would jeopardize the protection of heather moorland and Special Protection Areas for birds, large areas of which are keepered and which currently support high numbers of breeding waders.
5. Synthesis and applications . We agree with the study by Thirgood & Redpath that consideration of social and economic factors will be needed to resolve conflict but a reduction in management effort from driven to walked-up shooting is not the answer. A more satisfactory approach to the harrier : grouse conflict could be to try to reduce harrier predation by means of diversionary feeding and to address the problem of the rapid build-up in harrier numbers by exploring the use of a ceiling on harrier densities. 相似文献
2. We compare the bags, costs and incomes from these less intensive forms of grouse shooting with the more intensive driven shooting.
3. Allowing high density grouse moors to decline to low density ones will result in greater loss of income than the corresponding saving of costs. This can result in moor owners abandoning grouse management and thus gamekeepers losing their employment.
4. Losing gamekeepers from the uplands would jeopardize the protection of heather moorland and Special Protection Areas for birds, large areas of which are keepered and which currently support high numbers of breeding waders.
5. Synthesis and applications . We agree with the study by Thirgood & Redpath that consideration of social and economic factors will be needed to resolve conflict but a reduction in management effort from driven to walked-up shooting is not the answer. A more satisfactory approach to the harrier : grouse conflict could be to try to reduce harrier predation by means of diversionary feeding and to address the problem of the rapid build-up in harrier numbers by exploring the use of a ceiling on harrier densities. 相似文献