全文获取类型
收费全文 | 47649篇 |
免费 | 486篇 |
国内免费 | 430篇 |
专业分类
安全科学 | 1442篇 |
废物处理 | 2250篇 |
环保管理 | 5875篇 |
综合类 | 8034篇 |
基础理论 | 12223篇 |
环境理论 | 17篇 |
污染及防治 | 11952篇 |
评价与监测 | 3443篇 |
社会与环境 | 3034篇 |
灾害及防治 | 295篇 |
出版年
2023年 | 226篇 |
2022年 | 460篇 |
2021年 | 495篇 |
2020年 | 312篇 |
2019年 | 402篇 |
2018年 | 715篇 |
2017年 | 731篇 |
2016年 | 1156篇 |
2015年 | 833篇 |
2014年 | 1283篇 |
2013年 | 3849篇 |
2012年 | 1578篇 |
2011年 | 2019篇 |
2010年 | 1740篇 |
2009年 | 1796篇 |
2008年 | 2105篇 |
2007年 | 2163篇 |
2006年 | 1893篇 |
2005年 | 1653篇 |
2004年 | 1611篇 |
2003年 | 1571篇 |
2002年 | 1449篇 |
2001年 | 1795篇 |
2000年 | 1275篇 |
1999年 | 845篇 |
1998年 | 621篇 |
1997年 | 615篇 |
1996年 | 650篇 |
1995年 | 697篇 |
1994年 | 620篇 |
1993年 | 543篇 |
1992年 | 554篇 |
1991年 | 530篇 |
1990年 | 511篇 |
1989年 | 519篇 |
1988年 | 469篇 |
1987年 | 374篇 |
1986年 | 355篇 |
1985年 | 375篇 |
1984年 | 405篇 |
1983年 | 388篇 |
1982年 | 438篇 |
1981年 | 346篇 |
1980年 | 280篇 |
1979年 | 325篇 |
1978年 | 281篇 |
1977年 | 238篇 |
1976年 | 227篇 |
1975年 | 221篇 |
1973年 | 259篇 |
排序方式: 共有10000条查询结果,搜索用时 515 毫秒
811.
812.
813.
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
814.
815.
816.
Mitigation and Adaptation Strategies for Global Change - Guidelines of the Intergovernmental Panel on Climate Change (IPCC) were used to assess a greenhouse gas inventory for land use change and... 相似文献
817.
818.
819.
Flavonoid wing pigments increase attractiveness of female common blue (Polyommatus icarus) butterflies to mate-searching males 总被引:1,自引:0,他引:1
Common blue butterflies (Polyommatus icarus) sequester flavonoids from their larval host plants and allocate these UV-absorbing pigments to the wings. In field experiments
using dummies constructed from female butterflies, mate-searching males inspected flavonoid-rich dummies more intensively
than those with little or no flavonoids. Flavonoid content as signalled by UV-wing pattern may indicate ontogenetically determined
female quality or enhance detectability to males.
Received: 21 March 2000 / Accepted in revised form: 17 May 2000 相似文献
820.
The groundwater regime in Upper Palar basin, Tamilnadu has been highly contaminated in several locations due to discharge of effluents from a large number of tanneries. At some places total dissolved solids (TDS) concentration in groundwater was found as high as 8000 mg/l. Transmissivity and storativity of the regional aquifer were estimated at a few locations. The porosity and dispersivity values were not determined in the field. These parameters were assumed based on data available for similar geological formations elsewhere. The aquifer conceptualization thus arrived at formed the basis of a numerical groundwater flow model which was constructed using the finite difference method. The flow model was calibrated for steady state and then for transient condition for the period of 1984-92. The computed heads and calibrated parameters of the flow model were used to compute groundwater velocities. The migration of contaminants for a 20 year period was computed using the hydraulic heads and effective porosity value in a pathline model using FLOWPATH software. Mass transport model was constructed using Method of Characteristics (MOC) computer code in a separate model. The seepage rate of effluent is assumed at a rate of 30% of that discharged on the surface. The mass concentration of solute in the effluent reaching the water table was assumed as 40%, the same as in the surface effluent. The mass transport model was calibrated for a 20 year period. Prediction of contaminant migration from different clusters in the basin was analyzed. The prediction results indicated elevated TDS concentration of more than 4000 mg/l from most clusters. Also the area of the contaminated zone is likely to double in 20 years from contaminated zone of 1992. 相似文献