全文获取类型
收费全文 | 20418篇 |
免费 | 269篇 |
国内免费 | 182篇 |
专业分类
安全科学 | 729篇 |
废物处理 | 789篇 |
环保管理 | 3112篇 |
综合类 | 3015篇 |
基础理论 | 5501篇 |
环境理论 | 8篇 |
污染及防治 | 5233篇 |
评价与监测 | 1321篇 |
社会与环境 | 1016篇 |
灾害及防治 | 145篇 |
出版年
2022年 | 149篇 |
2021年 | 170篇 |
2020年 | 148篇 |
2019年 | 209篇 |
2018年 | 308篇 |
2017年 | 331篇 |
2016年 | 486篇 |
2015年 | 352篇 |
2014年 | 481篇 |
2013年 | 1630篇 |
2012年 | 617篇 |
2011年 | 864篇 |
2010年 | 723篇 |
2009年 | 722篇 |
2008年 | 893篇 |
2007年 | 908篇 |
2006年 | 874篇 |
2005年 | 679篇 |
2004年 | 731篇 |
2003年 | 667篇 |
2002年 | 627篇 |
2001年 | 803篇 |
2000年 | 553篇 |
1999年 | 346篇 |
1998年 | 293篇 |
1997年 | 284篇 |
1996年 | 288篇 |
1995年 | 303篇 |
1994年 | 328篇 |
1993年 | 270篇 |
1992年 | 288篇 |
1991年 | 254篇 |
1990年 | 288篇 |
1989年 | 266篇 |
1988年 | 215篇 |
1987年 | 190篇 |
1986年 | 179篇 |
1985年 | 194篇 |
1984年 | 215篇 |
1983年 | 207篇 |
1982年 | 206篇 |
1981年 | 212篇 |
1980年 | 162篇 |
1979年 | 170篇 |
1978年 | 149篇 |
1977年 | 125篇 |
1975年 | 125篇 |
1974年 | 122篇 |
1973年 | 116篇 |
1972年 | 138篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
331.
Gamergates (i.e. mated reproductive workers) are mostly known from ant species within the Ponerinae. We report here the discovery of gamergates in two species of the subfamily Myrmicinae. Until now, mated reproductive females in colonies of myrmicine species have been considered morphologically distinct from the worker caste. However, in two species of the myrmicine Metapone (Metapone madagascarica and a newly discovered, not yet described Metapone species) all workers have six ovarioles and a spermatheca; and some of them are mated. There are no morphological differences between mated and non-mated workers. Field observations and laboratory studies indicate that colonies of the Metapone species can reproduce with gamergates only. 相似文献
332.
Kurz Werner A. Beukema Sarah J. Apps Michael J. 《Mitigation and Adaptation Strategies for Global Change》1997,2(4):405-421
Land-use change from an unmanaged to a managed forested landscape in northern forests is associated with a reduction of the
area annually affected by natural disturbances (wildfires and forest insects) and the introduction of harvesting as a new
disturbance. This study examined the impacts of changes in the disturbance regime-the frequency and type of disturbance-on
landscape-level carbon (C) content and fluxes. The Carbon Budget Model of the Canadian Forest Sector was used to assess these
impacts in six representative landscapes (100,000 ha each) with a range of disturbance regimes that are characteristic of
conditions in coastal British Columbia, the interior of British Columbia, and the eastern boreal forest in Canada. The model
was used to simulate ecosystem C fluxes during a period of natural disturbances, a 50-year transition period during which
harvesting replaced natural disturbances, followed by 150 years of harvesting. The initial landscape-level biomass C content
under natural disturbance regimes in the six example landscapes was 22 to 75% of their potential maximum content which is
often used as the reference or baseline case. After 200 years of forest management, the C stored in the landscape plus the
C retained in forest products manufactured from harvested biomass was between 58 and 101% of the landscape C content prior
to the onset of harvesting. Landscape-level ecosystem C content was found to be affected by changes in the disturbance frequency,
the age-dependence of the disturbance probabilities, and the disturbance-specific impacts on ecosystem C content. The results
indicate that using the potential maximum C content of a landscape as the baseline always overestimates the actual C release
due to land use change. A more meaningful procedure would be to assess the actual differences in landscape-level C content
between the natural and the managed disturbance regime. 相似文献
333.
334.
Urban Flood Damage and Greenhouse Scenarios - The Implications for Policy: An Example from Australia
Urban flooding is often used as an illustration of the potentially adverse effects of greenhouse-induced climate change on extreme events. There is however, a paucity of studies that convert climate scenarios into changes in flood damage. This account summarises the use of modelling techniques, for three flood prone urban catchments in south eastern Australia, to assess changes to urban flood losses for the 'most wet' and 'most dry' scenarios for the year 2070. The most wet scenario indicates that annual average flood damage could increase within the range of 2.5 to 10 times, under the most dry scenario flood regimes would be similar to those experienced at present. The socio-economic scenarios based on the changes to flood losses are used to consider policy responses. It is unlikely that many local government authorities will respond because of lack of interest and because of major changes to the climate scenarios proposed over the last decade. Any response is likely to be incremental and accord with the 'no regrets' and the precautionary principle'. 相似文献
335.
336.
337.
338.
339.
340.
James N. Macri Kevin Spencer David Aitken Kenneth Garver Philip D. Buchanan Françoise Muller Andre Boue 《黑龙江环境通报》1993,13(7):557-562
Maternal serum free beta (hCG) levels are elevated (median 2·20 MOM) in the first trimester of pregnancy in 38 Down syndrome cases as compared with appropriate controls. This observation may form the basis for its use as a marker in screening for Down syndrome in the first trimester. Altered levels of the free beta analyte are observed in pregnancy conditions or complications other than Down syndrome. 相似文献