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181.
Ivan Valiela Deborah Rutecki Sophia Fox 《Journal of experimental marine biology and ecology》2004,300(1-2):131-159
This essay reviews two important topics in coastal ecology: the work on the relative role of bottom–up and top–down controls in natural communities and the loss of wetlands worldwide. In salt marshes and other coastal wetlands, bottom–up and top–down mechanisms of control on natural communities are pervasive. Bottom–up effects through nutrient supply may propagate to upper trophic levels via better food quality, or indirectly by altering water and sediment quality. Top–down control by consumers alters lower trophic levels through consumption of primary producers, and indirectly by trophic cascades in which higher predators feed on grazers. The combined forcing of bottom–up and top–down controls govern assemblages of species in natural communities, mediated by physical and biogeochemical factors. Although there is much information about biological controls of coastal food webs, more information is needed. Even more important is that large losses of wetland are occurring along coastlines worldwide due to a variety of economic and social activities including filling, wetland reclamation, and sediment interception. Such losses are of concern because these wetlands provide important functions, including export of energy-rich material to deeper waters, nursery and stock habitats, shoreline stabilization, and intercept land-derived nutrients and contaminants. These important functions justify conservation and restoration efforts; barring such efforts, we will find it increasingly difficult to find coastal wetlands where we can continue to gain further understanding of ecology and biogeochemistry and lack the aesthetic pleasure these wetlands provide to so many of us. 相似文献
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183.
Abstract. We compared the plant species composition, productivity and canopy structure of seven mown sites to a chronosequence of 20 abandoned calcareous fens in northeastern Switzerland. Cessation of mowing led to an 18% decline in overall plant species richness and the diversity of most functional groups. Abandonment did not lead to marked increases of above‐ground productivity, but rather selectively favoured certain functional groups. On abandoned fens biomass of grasses increased nearly threefold, at the expense of biomass of Cyperaceae and Juncaceae, which declined by 30% compared to mown fens, while forb biomass remained unaffected. Litter mass increased more than 15‐fold in fallows, while canopy height increased by 50%. The foliage in abandoned fens was oriented more horizontally and had a lower overall cover. However, these successional changes were never dependent upon the age of the fallow. Furthermore, nearly all traits differed significantly on regional and local spatial scales, suggesting that floristic and (meso‐)climatic differences obscure or override successional trajectories in these species‐rich wetlands. 相似文献
184.
湿地生态系统设计的一些基本问题探讨 总被引:54,自引:3,他引:51
湿地生态系统设计是恢复、调整湿地的重要手段,本文3从湿地生态系统设计概念入手,阐述了设计的基本原则。较详细地讨论了设计中的指标(水文指标、化学指标、基质指标和生物指标)要求,根据湿地生态系统设计的用途不同,探讨了3种主要的湿地生态系统设计类型,即作为废水处理湿地的设计,作为调整湿地的系统设计和作为洪水及非点源污染控制的湿地设计。 相似文献
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186.
Effects of agriculture and wetland restoration on hydrology, soils, and water quality of a Carolina bay complex 总被引:3,自引:0,他引:3
Gregory L. Bruland Matthew F. Hanchey Curtis J. Richardson 《Wetlands Ecology and Management》2003,11(3):141-156
We compared hydrology, soils, and water quality of an agricultural field (AG), a two-year-old restored wetland (RW), and two reference ecosystems (a non-riverine swamp forest (NRSF) and a high pocosin forest (POC)) located at the Barra Farms Regional Wetland Mitigation Bank, a Carolina bay complex in Cumberland County, North Carolina. Our main objectives were to: 1) determine if the RW exhibited hydrology comparable to a reference ecosystem, 2) characterize the soils of the AG, RW, and reference ecosystems, and 3) assess differences in water quality in the surface outflow from the AG, RW, and reference ecosystems. Water table data indicated that the hydrology of the RW has been successfully reestablished as the hydroperiod of the RW closely matched that of the NRSF in 1998 and 1999. Jurisdictional hydrologic success criterion was also met by the RW in both years. To characterize soil properties, soil cores from each ecosystem were analyzed for bulk density (Db), total carbon (Ct), nitrogen (Nt), and phosphorus (Pt), extractable phosphate (PO4w), nitrogen (Nex), and cations (Caex, Mgex, Kex, Naex), as well as pH. Bulk density, Pt, Caex, Mgex, and pH were greatly elevated in the AG and RW compared to the reference ecosystems. Water quality monitoring consisted of measuring soluble reactive phosphorus (SRP), total phosphorus (TP), nitrate + nitrite (NOX), and total nitrogen (TN) concentrations in surface water from the AG, RW, and reference outflows. Outflow concentrations of SRP, TP, and NOX were highest and most variable in the AG, while TN was highest in the reference. This study suggested that while restoration of wetland hydrology has been successful in the short term, alteration of wetland soil properties by agriculture was so intense, that changes due to restoration were not apparent for most soil parameters. Restoration also appeared to provide water quality benefits, as outflow concentrations of SRP, TP, NOX, and TN were lower in the RW than the AG. 相似文献
187.
Abstract. The wet to moist bryophyte‐dominated vegetation of Sassendalen, Svalbard, was classified into seven communities. These communities were grouped into (1) Cardamino nymanii‐Saxifragion foliolosae marsh; (2) Caricion stantis fen; (3) Luzulion nivalis snowbed – including manured vegetation corresponding to moss tundras. All communities have a basically arctic distribution. Marshes are developed in habitats with a water table above the bryophyte vegetation surface and fens on sites with a water table level high above the permafrost but below the bryophyte surface. Moss tundras normally have no standing water table, but in Sassendalen they have a low water table due to their development on less steep slopes than in their normal habitat near bird cliffs. CCA confirms that the standing water level is the prime differentiating factor between the alliances, while aspect favourability and permafrost depth differentiate between the fen communities and temporary desiccation is important for the Catoscopium nigritum community. Carex subspathacea is a characteristic fen species in the absence of other Carex species dominating elsewhere in the Arctic. Arctic marshes are linked to an extremely cold environment. They have a very low species diversity with a few species dominating; Arctophila fulva, Pseudocalliergon trifarium, Scorpidium scorpioides and Warnstorfia tundrae are character species. Moss tundra as defined here appears to be restricted to Svalbard and, probably, neighbouring Novaya Zemlya. This may be due to the absence of rodents and the high seabird density, which is related to the mild sea currents reaching further to the north here and which implies manuring of surrounding ecosystems. Manuring in a very cold environment produces moss carpets with a thin active layer and accumulation of thick peat layers without a standing water level. In Sassendalen the role of arctic seabirds is replaced by Svalbard reindeer which are nonmigratory and are concentrated to favourable grazing areas where their manuring effect is intense. Their long‐term manuring effect probably explains the occurrence of moss tundras in this weakly rolling landscape where seabird colonies are absent. 相似文献
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189.
This study estimates the economic values of and the dominant contributors to five key ecosystem services of wetlands in Beijing, by using the wetland inventory data in 2014 and economic valuation methods. Results indicate that the 51,434 ha of wetlands in Beijing annually provide 2.07 billion m3 of flood regulation, 944.01 million m3 of water provision, 42,154 tons of chemical oxygen demand (COD) purification, 3.03 PJ of heat absorption, and 9587 ha of habitat. Their economic values are estimated to be 15.89 billion RMB, 1.19 billion RMB, 169 million RMB, 421 million RMB, and 1.08 billion RMB in 2014 (RMB: Chinese currency, US$1 = RMB 6.14), respectively. The total values of five key wetland ecosystem services reach 18.76 billion RMB. In addition, the reservoir and river wetlands in Miyun, Yanqing, Fangshan, Huairou, and Mentougou Districts contribute 78% of key ecosystem services, whereas the urban wetlands in Xicheng, Dongcheng, Haidian, Chaoyang, and Tongzhou Districts more conveniently serve densely local people, hence they should be given particular attentions. In this paper, we develop the valuation methods of wetland ecosystem services, and recommend diversified strategies, regulations, and programs to protect the remaining wetlands in Beijing. This work can also provide a reference for the valuating of wetland ecosystem services for other urban-rural areas. 相似文献
190.
Sea level rise (SLR) is a primary factor responsible for inundation of low-lying coastal regions across the world, which in turn governs the agricultural productivity. In this study, rice (Oryza sativa L.) cultivated seasonally in the Kuttanad Wetland, a SLR prone region on the southwest coast of India, were analysed for oxygen, hydrogen and carbon isotopic ratios (δ18O, δ2H and δ13C) to distinguish the seasonal environmental conditions prevalent during rice cultivation. The region receives high rainfall during the wet season which promotes large supply of fresh water to the local water bodies via the rivers. In contrast, during the dry season reduced river discharge favours sea water incursion which adversely affects the rice cultivation. The water for rice cultivation is derived from regional water bodies that are characterised by seasonal salinity variation which co-varies with the δ18O and δ2H values. Rice cultivated during the wet and the dry season bears the isotopic imprints of this water. We explored the utility of a mechanistic model to quantify the contribution of two prominent factors, namely relative humidity and source water composition in governing the seasonal variation in oxygen isotopic composition of rice grain OM. δ13C values of rice grain OM were used to deduce the stress level by estimating the intrinsic water use efficiency (WUEi) of the crop during the two seasons. 1.3 times higher WUEi was exhibited by the same genotype during the dry season. The approach can be extended to other low lying coastal agro-ecosystems to infer the growth conditions of cultivated crops and can further be utilised for retrieving paleo-environmental information from well preserved archaeological plant remains. 相似文献