全文获取类型
收费全文 | 30817篇 |
免费 | 215篇 |
国内免费 | 165篇 |
专业分类
安全科学 | 568篇 |
废物处理 | 1591篇 |
环保管理 | 3864篇 |
综合类 | 4226篇 |
基础理论 | 8491篇 |
环境理论 | 7篇 |
污染及防治 | 7266篇 |
评价与监测 | 2405篇 |
社会与环境 | 2648篇 |
灾害及防治 | 131篇 |
出版年
2022年 | 170篇 |
2021年 | 200篇 |
2020年 | 135篇 |
2019年 | 195篇 |
2018年 | 1705篇 |
2017年 | 1635篇 |
2016年 | 1610篇 |
2015年 | 453篇 |
2014年 | 553篇 |
2013年 | 1728篇 |
2012年 | 1074篇 |
2011年 | 2118篇 |
2010年 | 1373篇 |
2009年 | 1290篇 |
2008年 | 1764篇 |
2007年 | 2110篇 |
2006年 | 893篇 |
2005年 | 748篇 |
2004年 | 826篇 |
2003年 | 768篇 |
2002年 | 740篇 |
2001年 | 916篇 |
2000年 | 639篇 |
1999年 | 354篇 |
1998年 | 296篇 |
1997年 | 281篇 |
1996年 | 278篇 |
1995年 | 317篇 |
1994年 | 321篇 |
1993年 | 269篇 |
1992年 | 290篇 |
1991年 | 268篇 |
1990年 | 314篇 |
1989年 | 282篇 |
1988年 | 229篇 |
1987年 | 205篇 |
1986年 | 199篇 |
1985年 | 211篇 |
1984年 | 238篇 |
1983年 | 217篇 |
1982年 | 222篇 |
1981年 | 207篇 |
1980年 | 173篇 |
1979年 | 191篇 |
1978年 | 154篇 |
1977年 | 143篇 |
1975年 | 142篇 |
1974年 | 142篇 |
1973年 | 140篇 |
1972年 | 162篇 |
排序方式: 共有10000条查询结果,搜索用时 303 毫秒
301.
302.
303.
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
304.
305.
V. Sivakumar V. Ravi Verma P.G. Rao G. Swaminathan 《Journal of Cleaner Production》2007,15(18):1813-1818
Focus on eco-friendly processing techniques makes vegetable tanning a viable option in leather processing and establishes the subsequent need for the more efficient methods of extraction in tannin manufacture. Application of ultrasound has been tried in the extraction of tannins from myrobalan nuts in order to improve the extraction efficiency, to perform the extraction under milder process conditions and to reduce the process time. The influence of process parameters such as ultrasonic output power, time and temperature has been studied. Scale-up trials and the use of ultrasound in pulse mode have also been attempted. The results show that a three- to fivefold improvement is possible with ultrasonic output from 20 to 100 W. Extraction efficiency has been calculated from the maximum extractable materials from myrobalan nuts. Extraction efficiency is found to be 90% for ultrasound, 100 W without external heating as compared to 77% for control process at 70 °C for 4 h. Therefore, ultrasound could be employed even dispensing with provision for temperature controls. The use of ultrasound in pulse mode offered 70% extraction efficiency of continuous mode. Scale-up trials indicate that there exists an optimum ultrasonic output power depending on the amount of nuts used, to achieve better extraction efficiency. The effectiveness of ultrasonically extracted tannin solution has also been tested in the tanning process for its applicability. The degree of tanning efficacy has been assessed by shrinkage temperature measurement. The results indicate that ultrasonically extracted tannin solution is suitable for tanning process. Therefore, application of ultrasound in tannin extract manufacture is a viable option with added advantages. 相似文献
306.
307.
Dr. Lauren Lynch James Bussel James D. Goldberg Usha Chitkara Isabelle Wilkins Jan Macfarland Richard L. Berkowitz 《黑龙江环境通报》1988,8(5):329-331
A case is presented in which percutaneous umbilical sampling (PUBS) was utilized in the second and third trimesters for the diagnosis and management of a pregnancy at risk for neonatal alloimmune thrombocytopenia (NAIT). 相似文献
308.
309.
310.