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   90627篇
  免费   1232篇
  国内免费   1099篇
安全科学   3764篇
废物处理   3386篇
环保管理   13757篇
综合类   21293篇
基础理论   26305篇
环境理论   77篇
污染及防治   14624篇
评价与监测   5545篇
社会与环境   3687篇
灾害及防治   520篇
  2022年   871篇
  2021年   902篇
  2020年   681篇
  2019年   907篇
  2018年   1221篇
  2017年   1238篇
  2016年   2267篇
  2015年   1883篇
  2014年   2689篇
  2013年   9405篇
  2012年   2273篇
  2011年   2471篇
  2010年   3313篇
  2009年   3439篇
  2008年   1953篇
  2007年   1835篇
  2006年   2227篇
  2005年   2245篇
  2004年   2512篇
  2003年   2362篇
  2002年   1870篇
  2001年   2119篇
  2000年   1920篇
  1999年   1486篇
  1998年   1361篇
  1997年   1340篇
  1996年   1465篇
  1995年   1565篇
  1994年   1452篇
  1993年   1303篇
  1992年   1300篇
  1991年   1267篇
  1990年   1215篇
  1989年   1181篇
  1988年   1026篇
  1987年   956篇
  1986年   985篇
  1985年   1053篇
  1984年   1149篇
  1983年   1164篇
  1982年   1172篇
  1981年   1089篇
  1980年   939篇
  1979年   909篇
  1978年   817篇
  1977年   715篇
  1976年   637篇
  1975年   602篇
  1973年   623篇
  1972年   630篇
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
341.
A test on social behavior as a cause of dispersal of spruce grouse   总被引:1,自引:0,他引:1  
Summary Social behavior is one hypothesized cause for dispersal. We tested this hypothesis on spruce grouse (Dendragapus canadensis) in two years by removing adults in summer and monitoring emigration of juveniles in autumn. Despite the absence of adults, juveniles emigrated from the natal range at rates comparable to juveniles on control areas. Data on density and dispersal from earlier spruce grouse studies are reviewed, which show that emigration is constant despite substantial differences in density, and that a clear female sex bias occurs across a wide range of densities. Results do not support the hypothesis that social behavior influences dispersal nor do they support a prediction of the Oedipus hypothesis that no sex bias occurs in polygynous birds. Offprint requests to: D.M. Keppie  相似文献   
342.
Summary The leaf gland volatile oils of ten sweet gale plants from a Scottish population were extracted in early summer. The results differed notably from reports of other populations in respect of the sesquiterpenes, -elemenone and germacrone, which were major components of the volatile oil. Three dihydrochalcones were also detected in the volatile oil. Variation within the population existed, particularly with respect to the relative importance of germacrone. Five plants were resampled in late summer and exhibited a marked reduction in -elemenone, a lesser reduction in germacrone and changes in the proportions of some monoterpenes.  相似文献   
343.
Temperature from 12 to 22°C and salinity from 30.5 to 7.6 increased accumulation of copper in Hediste diversicolor. Copper accumulated ranged from 85.83 to 217.14 g g-1. Sediments reduced accumulation of copper under temperature-salinity combinations. Accumulated copper ranged from 90.19 to 153.26 g g-1.However, mortality of the worms was not solely dependent upon copper body-burden. It ranged from 34 to 45% and from 38 to 80% in the presence of sediment. A combination of osmoregulatory and thermal stresses increased the toxic effect of copper to the worms.  相似文献   
344.
Without sediment, increasing salinity (7.3 to 29.2) and increasing temperature (12 to 22 °C) reduced the toxicity of copper to juvenile Hediste diversicolor. The LC50 values ranged from 357 gL-1 in 7.3 to 513 g L-1 in 29.2 at 12°C and from 247 to 500 g L-1 at 22°C. In deionized water all the juvenile were dead in all solutions to which copper was added (100 to 600 g L-1). Dead worms were swollen and everted their pharynxs. In higher doses of copper (500 to 600 g L-1) the worms were abnormal in behaviour in all salinities (0 to 29.2). The ability to swim or crawl was disturbed.With sediments increasing temperature and increasing salinity increased the toxicity of copper to the worms. The LC50 values ranged from 3200 to 4100 g L-1 at 22°C. The response of the juvenile to copper was antagonistic to increasing temperature and salinity and synergistic to increasing salinity and increasing temperature without and with the sediment respectively.  相似文献   
345.
Historical records from Ontario's Provincial Water Quality Monitoring Network (PWQMN) for rivers and streams were analyzed to assess the feasibility of mapping regional water quality patterns in southeastern Ontario which spans two major geologic zones, the Precambrian Shield and the St. Lawrence Lowlands, thus serving as a paradigm for much of Ontario. Despite biases toward the populated Lowlands and associated pollution problems, general spatial trends are evident via the analysis of intervariable relations, individual parameter maps and multivariate analysis. Using a robust algorithm designed to identify outliers and abstract underlying bivariate relations, a linear regional hardness-alkalinity relation was derived, where most anomalies proved to be mine drainage impacted sites. Regionally, multivariate ordination reveals that central tendencies of common indicators of ionic strength and nutrient richness correlate positively and that site clusters broadly reflect the transition from oligotrophic Shield waters to eutrophic conditions of heavily agricultural Lowland streams. Results suggest that on the Shield more precisely delineated aquatic regions may be realized by applying GIS to integrate river and synoptic lake survey data. Further synthesis with bedrock and surficial geology, physiography, pedology and other temporally invariant spatial attributes should yield regional patterns of background quality from which locally attainable water objectives might be defined. Additional synoptic surveys of sedimentary Lowland streams may be required as most available sites relflect anthropogenic pollution.  相似文献   
346.
Simmonds S  Cuttst F  Dick B 《Disasters》1985,9(1):61-69
Many problems have been encountered in the planning and implementation of health care in refugee camps, and more specifically in the training of refugees as primary health care workers. A review of the published literature and a "survey" of the opinions and experiences of refugee, national and international health personnel regarding training has therefore been undertaken to provide an overview of what has been done and to make recommendations for future work.
The review highlights the need to reallocate resources away from high visibility emergency aid to development activities, such as training, that will create an infrastructure for primary health care and promote self-reliance.  相似文献   
347.
Environment, Development and Sustainability - Environmental deterioration and global warming has created a substantial impact on international companies to incorporate eco-friendly, green supply...  相似文献   
348.
Environment, Development and Sustainability - Renewable energy (RE) plays an increasingly important role in the economy of almost every country in the world. In order to examine the state of...  相似文献   
349.
Environment, Development and Sustainability - This study describes the results of groundwater table variation in Thanjavur District before and after the monsoon seasons. Groundwater-level data...  相似文献   
350.
Russian Journal of Ecology - Populations at the border of ranges are considered more vulnerable than those in the center. However, some recent reviews contradict this hypothesis. We have studied...  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