首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   29825篇
  免费   357篇
  国内免费   517篇
安全科学   928篇
废物处理   1256篇
环保管理   3931篇
综合类   5781篇
基础理论   7368篇
环境理论   14篇
污染及防治   7624篇
评价与监测   1956篇
社会与环境   1649篇
灾害及防治   192篇
  2022年   282篇
  2021年   260篇
  2020年   251篇
  2019年   244篇
  2018年   455篇
  2017年   442篇
  2016年   664篇
  2015年   525篇
  2014年   790篇
  2013年   2302篇
  2012年   1006篇
  2011年   1394篇
  2010年   1087篇
  2009年   1198篇
  2008年   1314篇
  2007年   1354篇
  2006年   1185篇
  2005年   1022篇
  2004年   1007篇
  2003年   949篇
  2002年   897篇
  2001年   1120篇
  2000年   835篇
  1999年   534篇
  1998年   336篇
  1997年   364篇
  1996年   372篇
  1995年   426篇
  1994年   365篇
  1993年   320篇
  1992年   310篇
  1991年   330篇
  1990年   327篇
  1989年   300篇
  1988年   284篇
  1987年   222篇
  1986年   256篇
  1985年   252篇
  1984年   292篇
  1983年   241篇
  1982年   274篇
  1981年   259篇
  1980年   197篇
  1979年   232篇
  1978年   178篇
  1977年   170篇
  1976年   158篇
  1974年   181篇
  1972年   171篇
  1967年   158篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Paddy (rice) plants were dusted with 10% HCH containing 14C‐Γ‐HCH, at the rate of 2.5 kg a.i./ha and 14C‐residues were determined in different fractions of rice. Rice bran (0.187 ppm) had more of 14C‐residues than grain (0.026 ppm) and husk (0.042 ppm). The rice bran oil contained 0.129 ppm HCH residues. While degumming, dewaxing, alkali refining and bleaching had no effect, deodorisation alone eliminated 99.5% of added 14C‐residues in rice bran the oil during refining process.  相似文献   
952.
Thirty landraces of rice collected from various locations, across an elevational gradient (1150–2400 m asl), in Kumaun, Central Himalaya and VL-206 (a high-yielding variety recommended for rainfed mountain area) have been evaluated, both in terms of quantity and nutritional quality of straw. Data were collected to estimate the percentage share of fodder in the overall biomass produced. The total biomass harvested at maturity was taken as productivity. In view of the severe scarcity of fodder in hill regions, particularly during winter months, straw was also examined for quality-linked biochemical parameters and dry matter digestibility (DMD) of fodder. The Crude Protein (CP) values ranged from 2.21% (Nandhani) to 6.33% (Dalbadal), and in saceo DMD (nylonbag technique) was highest in Kaladur (48.84%) and lowest in Kantolia (32.25%). While the CP in VL206 was within the range recorded for various landraces (3.61%), DMD value (27.29%) was lower than that of all the landraces tested. In saceo DMD data indicate that the fodder quality of landraces is better than that of the introduced variety. The values for neutral detergent fibre (NDF) ranged from 63.64% (Sabhawati) to 78.46% (Chhotiya) among the rainfed landraces, while in the irrigated landraces, Thapchini had more NDF (87.50 %), as compared to Kantolia (73.88%) and VL206 (74.91%). Values for the acid detergent fibre (ADF) varied from 42.70% (Danbasmati) to 54.58% (Nandhani) in the rainfed group; ADF was slightly higher in Thapchini (49.41%) in comparison to Kantolia (47.19) and VL206 had the highest (56.80%) ADF content. The observed differences with respect to straw productivity, chemical composition and in saceo DMD in various landraces, even when grown under similar conditions at one place, clearly indicate the richness of the gene pool of rice being maintained, through cultivation, in the Kumaun hills. It may be mentioned that agriculture in the hills is biomass based, and livestock form an integral component of subsistence farming.  相似文献   
953.
Ecological regionalization is a base for rational management and sustainable utilization of ecosystems and natural resources. It can provide a scientific basis for constructing healthy ecological environments and making policies of environmental management. In this paper, based on synthetic analysis of the characteristics of the ecology and environments of China, the principles of ecological regionalization are discussed, and indices and nomenclature of ecological regionalization are proposed. The ecoregions on a national scale are divided. The results show that there are 3 domains, 13 ecoregions and 57 ecodistricts. The present scheme can be used as a framework for ecosystem assessment and management. Based on the ecoregions, measurements of management for forest, grassland, agriculture and wetland ecosystems are recommended. The experience and information can be used within and beyond the national scale for land-use planning, biodiversity conservation and ecosystem restoration.  相似文献   
954.
Conservation is increasingly promoted as a sustainable development instrument in Southern Africa, particularly for remote rural communities. Conservation and development schemes are marketed as community-based projects providing local empowerment through the creation of jobs and cash stemming from protected areas, as well as increased biodiversity protection by local communities whose jobs are dependent on the resource. Transfrontier Conservation Areas (TFCAs), mega Peace Parks that cross international borders, are one of the latest conservation and development paradigms in Southern Africa. TFCAs have gained broad support, including government recognition as a development tool. However, there has been minimal research on the impact of TFCAs on local communities. This paper seeks to provide an empirical case study of a South African community bordering the Lubombo TFCA (South Africa, Swaziland, Mozambique). Results are presented that indicate the Mbangweni community in KwaZulu-Natal could experience decreased access to social, natural, and economic resources as a result of the Peace Park.  相似文献   
955.
Long-term decadal retrospection in spatio-temporal imagery analyses can only be carried out using aerial photographs, which are still the most detailed remotely sensed data available. Visual interpretation of such imagery is most efficient and inexpensive in the light of ecosystem monitoring research in developing countries, which are often unable to cope with the development or the cost of acquisition of commercial space-borne imaging (e.g. IKONOS, Quickbird). In this light, the present paper explicitly analyses the methodological use of image attributes of air-borne imagery from mangrove forests, and investigates the consistency and constraints of mangrove image attributes in visually interpreted air-borne imagery. Six image attributes are analysed, and their application is illustrated using various mangrove sites in Kenya and Sri Lanka. Comparison of identification keys reveals that minor attributes such as 'ecological position' are informative, and that image attributes for a particular species or genus are apparently less plastic and more widely applicable than formerly assumed. Emphasis on compulsory fieldwork is made and constraints related to reflection and interference, amongst others, are discussed.  相似文献   
956.
Indigenous ecological knowledge (IEK) of Borana pastoralists on strategies of sustainable resource utilization, forage species, ecological interactions, rangeland condition and trend was documented using discussions, a semi-structured questionnaire survey and analytical workshops. Traditional strategies of rangeland and water management were described and the most important forage species identified. Pastoralists' perceptions were compared across age, gender and site. There was a positive correlation between pastoralists' preference ranking of forage species and crude protein content of the species. IEK of men and women was complementary. The process of rangeland degradation was described as shortage of grass and decrease in density and frequency of highly palatable grass species, leading to low milk production and reduced conception rates in cows. The results confirmed that the IEK of these pastoralists could still provide the basis for sustainable resource utilization and rangeland rehabilitation. However, the young generation in the area had not only limited knowledge but also showed less interest to learn and apply the traditional resource management strategies. Therefore, there is high need to perpetuate, document and use this IEK for sustainable development. On the other hand, shortage of forage resources as a result of rangeland shrinkage (leading to rangeland degradation and woody plants encroachment), less application of IEK, the gap between traditional and formal systems, and trends of disobeying traditional rules and regulations were identified as current challenges for the Borana pastoralists.  相似文献   
957.
Desertification is the spread of desert-like conditions in arid and semi-arid conditions. It is a result of pressure from both climatic and human factors. Desertification in the Sudan has been accelerating at a faster rate over the last two decades, leading to marginalization and the loss of arable land. The main factors contributing to desertification include drought, population growth, the spread of extensive agriculture, deforestation, rapid urbanization, the erosion of local political power, the lack of economic institutions and the absence of social institutions which have tended to reduce the capacity of the local people to cope with the resource degradation problem. Initiatives to arrest the desert encroachment must include improved cultivation methods, proper grazing management, reforestation and integration of livestock and crop production systems, coupled with good linkages to light processing industries.

This paper identifies the causal factors of desert encroachment, assesses its impact on the environment and humanity and concludes by recommending specific strategies to control the desert encroachment problem.  相似文献   
958.
The biomarker approach has been used for 25 years to study the environmental quality of marine, brackish and freshwater ecosystems. Biomarkers may indicate health status and can be applied to organisms of all zoological phyla by destructive or non destructive methods. For 5 years we have been using this approach in zooplankton to detect ecotoxicological alterations at low levels of the food chain due to contaminants. Here we review our approach to validate and apply biomarker techniques in zooplankton. We discuss advantages, limitations, some results and future research. We indicate that biomarkers in zooplankton can be used as new indices of trophic status and ecological integrity of Italian marine coastal and lagoon environments, to be included among the tools specified by Italian law D.Lgs. 152/2006.  相似文献   
959.
Abstract

Standardized tests were applied to aromatic and polar fractions of sediment extracts to determine whether polar constituents or oxidative degradation products contributed significantly to the toxicity of sediments oiled by the Exxon Valdez spill. Intertidal sediment and pore-water samples were collected in September 1990 from two heavily oiled sites and an unoiled site in Prince William Sound (PWS). Methylene chloride extracts from these samples were fractionated by liquid chromatography into aliphatic, aromatic and polar fractions, and the aromatic and polar fractions were tested for toxicity using the MicrotoxR test, bivalve larval mortality and development (Mytilus); several measures of genotoxicity in Mytilus, including SOS ChromotestR, anaphase aberrations and sister chromatid exchange; and survival, anaphase aberrations and teratogenicity in coho salmon (Onchorhynchus kisutch). MicrotoxR and SOS ChromotestR protocols were applied in a screening mode to all samples, whereas other tests were applied only to selected fractions from two sites. Samples from Bay of Isles (oiled) were consistently more toxic (usually only 2 to 5-fold) than the Mooselips Bay (unoiled) samples, which gave very low responses in all tests. for both sites, however, responses to polar and aromatic fractions were about the same in most tests, suggesting that while the overall toxicity of the oil was low in these samples, at least part of that toxicity was derived from polar constituents. Compared to the parent hydrocarbons, polar oxidation products partition preferentially into pore-water and are more rapidly diluted and dispersed in the water column. These results suggest that polar oxidation products of petroleum hydrocarbons pose little risk to marine organisms, except possibly for infauna continuously exposed to pore-water in heavily oiled sediments. Independent surveys showed that sediment toxicity in PWS declined during 1989–1991 to near background levels, in accord with previous understanding of oil weathering and toxicity.  相似文献   
960.
SUMMARY

The search for innovative methods for improving relations between parks and people has led to various conservation and development projects around the world. Nepal's almost three decades of experience in park management in a variety of institutional settings offers valuable lessons in the challenges and opportunities for enlisting local support for conservation. Citing several macro and micro-level case studies from around the country, this paper provides a comparative perspective on the significance of tourism-focused conservation and community development activities in resolving conflicts between parks and local people.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号