全文获取类型
收费全文 | 4040篇 |
免费 | 413篇 |
国内免费 | 1125篇 |
专业分类
安全科学 | 447篇 |
废物处理 | 150篇 |
环保管理 | 331篇 |
综合类 | 2583篇 |
基础理论 | 591篇 |
污染及防治 | 785篇 |
评价与监测 | 229篇 |
社会与环境 | 311篇 |
灾害及防治 | 151篇 |
出版年
2024年 | 14篇 |
2023年 | 78篇 |
2022年 | 223篇 |
2021年 | 209篇 |
2020年 | 205篇 |
2019年 | 153篇 |
2018年 | 150篇 |
2017年 | 175篇 |
2016年 | 168篇 |
2015年 | 223篇 |
2014年 | 260篇 |
2013年 | 345篇 |
2012年 | 318篇 |
2011年 | 350篇 |
2010年 | 291篇 |
2009年 | 280篇 |
2008年 | 295篇 |
2007年 | 296篇 |
2006年 | 334篇 |
2005年 | 250篇 |
2004年 | 160篇 |
2003年 | 146篇 |
2002年 | 123篇 |
2001年 | 96篇 |
2000年 | 91篇 |
1999年 | 71篇 |
1998年 | 37篇 |
1997年 | 40篇 |
1996年 | 40篇 |
1995年 | 31篇 |
1994年 | 34篇 |
1993年 | 33篇 |
1992年 | 15篇 |
1991年 | 12篇 |
1990年 | 10篇 |
1989年 | 5篇 |
1988年 | 8篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1982年 | 3篇 |
排序方式: 共有5578条查询结果,搜索用时 31 毫秒
281.
282.
Agricultural Productivity Changes Induced by the Sloping Land Conversion Program: An Analysis of Wuqi County in the Loess Plateau Region 总被引:3,自引:0,他引:3
This paper examines the agricultural productivity change induced by the Sloping Land Conversion Program (SLCP) using the Malmquist
index method and household data collected from Wuqi. We find that during the period of 1998–2004, the total factor productivity
(TFP) grew by 15.8%. While numerous households suffered a TFP decline, the majority of them experienced a large gain. By decomposing
the TFP, we further show that its increase is due exclusively to the improvement of technical efficiency rather than to technological
change. To validate these findings and put them in perspective, we also estimated the TFP change with county-level aggregate
data. It is revealed that driven by technological change and scale efficiency, the TFP grew slightly during the period of
1992–1998. Because of the tremendous cropland reduction and production mode shift caused by implementing the SLCP, the TFP
declined substantially during the first three years of the program; due to continued improvement of technical efficiency;
however, its growth accelerated later. Altogether, our evidence consistently suggests that implementing the SLCP has contributed
to the agricultural TFP growth in the longer term and that the efficiency improvement has resulted mainly from the increased
public expenditures for extension services and diffusion of technical knowledge. Wuqi’s experience proves that it is possible
to achieve environmental conservation and increase productivity simultaneously, even when facing a cropland reduction and
production mode alternation. 相似文献
283.
青岛市废有机溶剂现状分析与评价 总被引:1,自引:0,他引:1
调查分析青岛市废有机溶剂产生现状、污染特性、处置流向及回收利用的概况。结合青岛市产业结构特点,遵循"资源化、减量化、无害化"处置原则,提出废有机溶剂管理的对策和建议。研究结果对危险废物的有效管理和促进循环经济发展具有指导意义。 相似文献
284.
285.
研究了废旧冰箱聚氨酯(PUR)泡沫中所含的一氟三氯甲烷(CFC-11)总量,并对冰箱箱体切割过程、金属板剥离过程和PUR泡沫破碎后常温放置时的CFC-11释放量进行了测定。结果表明,PUR泡沫所含CFC-11总量占PUR泡沫质量的20.06%;箱体切割和金属板剥离过程中的CFC-11释放量分别占PUR泡沫中CFC-11总量的0.75%和2.32%;常温放置到第15天时,0.5、1.0、4.0、8.0 mm 4种粒径PUR泡沫颗粒的CFC-11累计释放量分别占PUR泡沫所含CFC-11总量的4.75%、5.25%、5.42%、6.50%,均高于箱体切割、金属板剥离过程中的CFC-11释放量。 相似文献
286.
Jianjun Chen Qi Ying Michael J. Kleeman 《Atmospheric environment (Oxford, England : 1994)》2010,44(10):1331-1340
The UCD/CIT air quality model with the Caltech Atmospheric Chemistry Mechanism (CACM) was used to predict source contributions to secondary organic aerosol (SOA) formation in the San Joaquin Valley (SJV) from December 15, 2000 to January 7, 2001. The predicted 24-day average SOA concentration had a maximum value of 4.26 μg m?3 50 km southwest of Fresno. Predicted SOA concentrations at Fresno, Angiola, and Bakersfield were 2.46 μg m?3, 1.68 μg m?3, and 2.28 μg m?3, respectively, accounting for 6%, 37%, and 4% of the total predicted organic aerosol. The average SOA concentration across the entire SJV was 1.35 μg m?3, which accounts for approximately 20% of the total predicted organic aerosol. Averaged over the entire SJV, the major SOA sources were solvent use (28% of SOA), catalyst gasoline engines (25% of SOA), wood smoke (16% of SOA), non-catalyst gasoline engines (13% of SOA), and other anthropogenic sources (11% of SOA). Diesel engines were predicted to only account for approximately 2% of the total SOA formation in the SJV because they emit a small amount of volatile organic compounds relative to other sources. In terms of SOA precursors within the SJV, long-chain alkanes were predicted to be the largest SOA contributor, followed by aromatic compounds. The current study identifies the major known contributors to the SOA burden during a winter pollution episode in the SJV, with further enhancements possible as additional formation pathways are discovered. 相似文献
287.
Renbin Zhu Yashu Liu Hua Xu Tao Huang Jianjun Sun Erdeng Ma Liguang Sun 《Atmospheric environment (Oxford, England : 1994)》2010,44(3):304-311
During the summertime of 2007/2008, carbon dioxide (CO2) and methane (CH4) fluxes across air–water interface were investigated in the littoral zones of Lake Mochou and Lake Tuanjie, east Antarctica, using a static chamber technique. The mean fluxes of CO2 and CH4 were ?70.8 mgCO2 m?2 h?1 and 144.6 μgCH4 m?2 h?1, respectively, in the littoral zone of Lake Mochou; The mean fluxes were ?36.9 mgCO2 m?2 h?1 and 109.8 μgCH4 m?2 h?1, respectively, in the littoral zone of Lake Tuanjie. Their fluxes showed large temporal and spatial dynamics. The CO2 fluxes showed a significantly negative correlation with daily total radiation (DTR) and a weakly negative correlation with air temperature and water temperature, indicating that sunlight intensity controlled the magnitude of CO2 fluxes from the open lakes. The CH4 fluxes significantly correlated with local air temperature, water table and total dissolved solids (TDS), indicating that they were the predominant factors influencing CH4 fluxes. Summertime CO2 budgets in the littoral zones of Lake Mochou and Lake Tuanjie were estimated to be ?152.9 gCO2 m?2 and ?79.7 gCO2 m?2, respectively, and net CH4 emissions were estimated to be 312.3 mgCH4 m?2 and 237.2 mgCH4 m?2, respectively. Our results show that shallow, open, alga-rich lakes might be strong summertime CO2 absorbers and small CH4 emitters during the open water in coastal Antarctica. 相似文献
288.
偕胺肟合铁(Ⅲ)纤维对α-萘酚的吸附 总被引:1,自引:0,他引:1
以腈纶纤维为原料络合Fe3+制得偕胺肟合铁(Ⅲ)纤维,用其处理α-萘酚溶液,研究了偕胺肟合铁(Ⅲ)纤维对α-萘酚的吸附工艺条件和吸附动力学参数。实验结果表明,偕胺肟合铁(Ⅲ)纤维对α-萘酚的最佳吸附工艺条件为pH=3.0、吸附温度313.15K和吸附时间45min。在最佳工艺条件下,偕胺肟合铁(Ⅲ)纤维对α-萘酚的吸附在所研究的α-萘酚浓度范围内符合Freundlich等温吸附方程。未达到饱和吸附前,偕胺肟合铁(Ⅲ)纤维对α-萘酚的吸附符合一级反应动力学特征。 相似文献
289.
中国能源生态足迹的时空动态特征及效应分析 总被引:1,自引:0,他引:1
运用生态足迹方法计算出1990—2007年中国能源消费的生态足迹。在此基础上,分析了能源足迹强度(EFI)、能源足迹生态压力(EPIEF)的时空动态变化特征。结果表明,近20年来我国能源足迹波动上升,能源消费结构有所改善,但煤炭足迹仍占主导,近几年又有回升趋势;能源足迹强度呈幂指数衰减,能源利用效率不断提高;EPIEF呈上升趋势,说明能源利用对自然生态系统的压力逐渐增大。在空间分布上,各省区能源足迹差异显著,能源足迹强度由西向东逐渐降低,而EPIEF则由西向东呈增大趋势。依据EPIEF指数将中国30个省区划分为能源足迹生态盈余区(EPIEF1)、生态轻度亏损区(1EPIEF5)和生态严重亏损区(EPIEF5)3种类型。 相似文献
290.