全文获取类型
收费全文 | 1275篇 |
免费 | 90篇 |
国内免费 | 177篇 |
专业分类
安全科学 | 180篇 |
废物处理 | 14篇 |
环保管理 | 278篇 |
综合类 | 418篇 |
基础理论 | 361篇 |
环境理论 | 1篇 |
污染及防治 | 113篇 |
评价与监测 | 29篇 |
社会与环境 | 121篇 |
灾害及防治 | 27篇 |
出版年
2024年 | 1篇 |
2023年 | 23篇 |
2022年 | 38篇 |
2021年 | 50篇 |
2020年 | 48篇 |
2019年 | 37篇 |
2018年 | 34篇 |
2017年 | 42篇 |
2016年 | 60篇 |
2015年 | 55篇 |
2014年 | 43篇 |
2013年 | 68篇 |
2012年 | 81篇 |
2011年 | 135篇 |
2010年 | 71篇 |
2009年 | 106篇 |
2008年 | 79篇 |
2007年 | 80篇 |
2006年 | 86篇 |
2005年 | 45篇 |
2004年 | 51篇 |
2003年 | 38篇 |
2002年 | 42篇 |
2001年 | 35篇 |
2000年 | 35篇 |
1999年 | 21篇 |
1998年 | 15篇 |
1997年 | 16篇 |
1996年 | 18篇 |
1995年 | 16篇 |
1994年 | 10篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 4篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
排序方式: 共有1542条查询结果,搜索用时 15 毫秒
271.
The crucial parameter used to calculate turbulence effects upon light waves propagating through the atmosphere is known as
the structure constant, . As Tatarski has shown, this parameter depends upon the “outer scale” of the inertial sub-range of the turbulence. Recently
there have been successful predictions of astronomical “seeing” conditions at Mauna Kea Astronomical Observatory which have
increased interest in this subject and in the use of the so-called “Dewan Optical Turbulence Model”. In the case of the Air
Force, there has been a longstanding need for such optical turbulence prediction, especially in the stratosphere. In the past
researchers have used a relation due to Tatarski, (which plays a prominent role in this model) in order to deduce values of
the “outer scale” from measurements. When doing this, they have been surprised to find values very much smaller than expected. The goal of the paper
is to explain this unexpected result. As we will show, this result can be explained by two factors: (a) the average turbulent
layer thicknesses are smaller than originally believed, and, more importantly, (b) only a minor fraction of the stratosphere
is turbulent. In order to arrive at this conclusion, we used the high-resolution (10 m) wind profiles that were originally
used to formulate the previously mentioned optical turbulence model.
The U.S. Government’s right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged. 相似文献
272.
Alberto Pivato Stefano Vanin Luca Palmeri Alberto Barausse Giovanni Mangione Michele Rasera Monego Gianluca 《Waste management (New York, N.Y.)》2013,33(7):1607-1615
The Biopotentiality Index is a landscape ecology indicator, which can be used to estimate the latent energy of a given land and to assess the environmental impacts due to the loss of naturalness on a landscape scale. This indicator has been applied to estimate the effectiveness of the measures put in place to provide an environmental compensation for the revamping of a composting plant. These compensation measures are represented by a green belt with a minimum width of 25 m all around the plant, representing both a windbreak and a buffer zone, and by two wide wooded zones acting as core natural areas.This case-study shows that the compensation index could be used as a key tool in order to negotiate the acceptance of waste treatment plant with the population. 相似文献
273.
海底铁锰氧化还原过程的模拟研究 总被引:5,自引:0,他引:5
本文用室内海水-沉积物平衡箱研究了沉积物间隙水中铁、锰的垂直变化分布和随时间变化的分布,Fe~(2+)随深度、时间的变化幅度大,在六个月的实验期内均是如此,而Mn~(2+)在放置三个月后即趋于稳定;Fe~(2+),Mn~(2+)产生的宏观经验动力学表明:Fe~(2+)受pH影响远比Mn~(2+)大,且随着深度的增加更为明显,Fe~(2+)在较下层产生速率大,而Mn~(2+)反之;Fe~(2+)的扩散转移是上覆海水向沉积物中转移,扩散量为-60.7ug/m~2d,Nn~(2+)转移方向相反,扩散量为1746.2ug/m~2.d。 相似文献
274.
分析了毛细饱水带的水动力学特性,指出在地下水污染研究中,污染物在毛细饱和水带和潜水怪具有相同的水平运动规律,并以实例分析说明该带对污染物运移的重要性。建议在研究和一非饱和条件地下水及污染物运动问题时把毛细饱水带与潜水含水层统一为饱马毛细饱水带顶面作为饱水面。 相似文献
275.
276.
The concept of time perspective balance has attracted increased attention from scholars in the past decade, reflected in published evidence suggesting positive outcomes ranging from enhanced mood to life satisfaction for those individuals possessing balance among their past, present, and future time perspectives, and assumedly able to shift their time perspective to match situational demands. In this paper, we consider the notion of time perspective balance in an organizational setting within which much consequential adaptation often occurs—the team environment—and explore different configurations of time perspective balance in teams facing dynamic task contexts. Drawing from work on situational awareness, we first consider the mechanism by which time perspective balance likely influences individual adaptation in dynamic task-focused situations. Next, we postulate what types of team configurations—ones with more balanced time perspective uniformity or ones with more time perspective variety—might be more appropriate in dynamic contexts given key team conditions. We illustrate our analysis with examples from healthcare team settings and offer ideas for future research. 相似文献
277.
Surface runoff is one of the most important pathways for pesticides to enter surface waters. Mathematical models are employed to characterize its spatio-temporal variability within landscapes, but they must be simple owing to the limited availability and low resolution of data at this scale. This study aimed to validate a simplified spatially-explicit model that is developed for the regional scale to calculate the runoff potential (RP). The RP is a generic indicator of the magnitude of pesticide inputs into streams via runoff. The underlying runoff model considers key environmental factors affecting runoff (precipitation, topography, land use, and soil characteristics), but predicts losses of a generic substance instead of any one pesticide. We predicted and evaluated RP for 20 small streams. RP input data were extracted from governmental databases. Pesticide measurements from a triennial study were used for validation. Measured pesticide concentrations were standardized by the applied mass per catchment and the water solubility of the relevant compounds. The maximum standardized concentration per site and year (runoff loss, RLoss) provided a generalized measure of observed pesticide inputs into the streams. Average RP explained 75% (p < 0.001) of the variance in RLoss. Our results imply that the generic indicator can give an adequate estimate of runoff inputs into small streams, wherever data of similar resolution are available. Therefore, we suggest RP for a first quick and cost-effective location of potential runoff hot spots at the landscape level. 相似文献
278.
S. O. Oikeh R. J. Carsky J. G. Kling V. O. Chude W. J. Horst 《Agriculture, ecosystems & environment》2003,100(2-3):181
Nitrate is prone to leaching in the sandy soils of the West African moist savannas. Better management of nitrogen (N) resources and maize cultivars with enhanced genetic capacity to capture and utilize soil and fertilizer N are strategies that could improve N-use efficiency. In two field experiments conducted at Zaria, northern Nigeria, five maize (Zea mays L.) cultivars planted early in the season were assessed under various N levels for differences in N uptake, soil N dynamics, and related N losses. Cultivar TZB-SR accumulated more N in the aboveground plant parts in both years than the other cultivars. All, except the semi-prolific late (SPL) variety, met about 50–60% of their N demand by the time of silking (64–69 DAP). In both years, SPL had the greatest capacity to take up N during the grain filling period, and it had the highest grain-N concentration and the least apparent N loss through leaching in the second year. There were no significant differences in soil N dynamics among cultivars in both years. At harvest, the residual N in the upper 90 cm of the profile under all the cultivars ranged from 56 to 72 kg ha−1 in the first year and from 73 to 83 kg ha−1 in the second year. Apparent N loss from 0 to 90 cm soil profile through leaching ranged from 35 to 122 kg ha−1 in both years. N application significantly increased N uptake by more than 30% at all sampling dates in the second year of the experiment, but had no effect on apparent N loss. Results indicate that the use of maize cultivars with high N uptake capacity during the grain filling period when maximum leaching losses occur could enhance N recovery and may be effective in reducing leaching losses of mineral N in the moist savanna soils. 相似文献
280.