全文获取类型
收费全文 | 11331篇 |
免费 | 9篇 |
国内免费 | 2篇 |
专业分类
安全科学 | 35篇 |
废物处理 | 817篇 |
环保管理 | 1301篇 |
综合类 | 1560篇 |
基础理论 | 3377篇 |
环境理论 | 7篇 |
污染及防治 | 2205篇 |
评价与监测 | 1083篇 |
社会与环境 | 955篇 |
灾害及防治 | 2篇 |
出版年
2021年 | 15篇 |
2020年 | 13篇 |
2019年 | 16篇 |
2018年 | 1487篇 |
2017年 | 1394篇 |
2016年 | 1218篇 |
2015年 | 151篇 |
2014年 | 57篇 |
2013年 | 97篇 |
2012年 | 489篇 |
2011年 | 1395篇 |
2010年 | 729篇 |
2009年 | 648篇 |
2008年 | 945篇 |
2007年 | 1292篇 |
2006年 | 67篇 |
2005年 | 82篇 |
2004年 | 70篇 |
2003年 | 105篇 |
2002年 | 139篇 |
2001年 | 70篇 |
2000年 | 47篇 |
1999年 | 29篇 |
1998年 | 26篇 |
1997年 | 18篇 |
1996年 | 17篇 |
1995年 | 18篇 |
1994年 | 30篇 |
1993年 | 13篇 |
1991年 | 15篇 |
1984年 | 25篇 |
1983年 | 17篇 |
1981年 | 16篇 |
1975年 | 12篇 |
1974年 | 12篇 |
1969年 | 14篇 |
1968年 | 13篇 |
1967年 | 15篇 |
1966年 | 23篇 |
1965年 | 29篇 |
1964年 | 16篇 |
1963年 | 25篇 |
1962年 | 22篇 |
1961年 | 30篇 |
1960年 | 20篇 |
1959年 | 21篇 |
1958年 | 13篇 |
1957年 | 24篇 |
1956年 | 16篇 |
1955年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
44.
A Simulation of Temporal and Spatial Variations in Carbon at Landscape Level: A Case Study for Lake Abitibi Model Forest in Ontario,Canada 总被引:2,自引:0,他引:2
Xiaolu Zhou Changhui Peng Qing-Lai Dang Jiaxin Chen Sue Parton 《Mitigation and Adaptation Strategies for Global Change》2007,12(4):525-543
Using a case study of the Lake Abitibi Model Forest (LAMF), this study aims to assess the temporal and spatial variability
in carbon storage during 1990–2000, and to present a comprehensive estimation of the carbon budget for LAMF's ecosystems.
As well, it provided the information needed by local forest managers to develop ecological and carbon-based indicators and
monitor the sustainability of forest ecosystems. Temporal and spatial carbon dynamics were simulated at the landscape level
using ecosystem model TRIPLEX1.0 and Geographical Information System (GIS). The simulated net primary productivity (NPP) and
carbon storage in forest biomass and soil were compared with field data and results from other studies for Canada's boreal
forests. The results show that simulated NPP ranged from 3.26 to 3.34 tC ha−1 yr−1 in the 1990s and was consistent with the range measured during the Boreal Ecosystem-Atmosphere Studies (BOREAS) in central
Canada. Modeled NPP was also compared with the estimation from remote sensing data. The density of total above-and belowground
biomass was 125.3, 111.8, and 106.5 tC ha−1 for black spruce, trembling aspen, and jack pine in the LAMF ecosystem, respectively. The total carbon density of forested
land was estimated at 154.4 tC ha−1 with the proportion of 4:6 for total biomass and soil. The analysis of net carbon balance of ecosystem suggested that the
LAMF forest ecosystem was acting as a carbon sink with an allowable harvest in the 1990s. 相似文献
45.
46.
In angiosperms, archesporial cells in the anther primordium undergo meiosis to form haploid pollen, the sole occupants of anther sacs. Anther sacs are held together by a matrix of parenchyma cells, the connective tissue. Cells of the connective tissue are not known to differentiate. We report the differentiation of parenchyma cells in the connective tissue of two Gordonia species into pollen-like structures (described as pseudopollen), which migrate into the anther sacs before dehiscence. Pollen and pseudopollen were distinguishable by morphology and staining. Pollen were tricolpate to spherical while pseudopollen were less rigid and transparent with a ribbed surface. Both types were different in size, shape, staining and surface architecture. The ratio of the number of pseudopollen to pollen was 1:3. During ontogeny in the connective tissue, neither cell division nor tetrad formation was observed and hence pseudopollen were presumed to be diploid. Only normal pollen germinated on a germination medium. Fixed preparations in time seemed to indicate that pseudopollen migrate from the connective tissue into the anther sac. 相似文献
47.
48.
49.
50.