全文获取类型
收费全文 | 2761篇 |
免费 | 260篇 |
国内免费 | 600篇 |
专业分类
安全科学 | 467篇 |
废物处理 | 78篇 |
环保管理 | 567篇 |
综合类 | 1315篇 |
基础理论 | 360篇 |
污染及防治 | 322篇 |
评价与监测 | 111篇 |
社会与环境 | 152篇 |
灾害及防治 | 249篇 |
出版年
2024年 | 9篇 |
2023年 | 26篇 |
2022年 | 81篇 |
2021年 | 92篇 |
2020年 | 104篇 |
2019年 | 73篇 |
2018年 | 82篇 |
2017年 | 115篇 |
2016年 | 135篇 |
2015年 | 151篇 |
2014年 | 160篇 |
2013年 | 206篇 |
2012年 | 221篇 |
2011年 | 233篇 |
2010年 | 176篇 |
2009年 | 197篇 |
2008年 | 141篇 |
2007年 | 204篇 |
2006年 | 167篇 |
2005年 | 163篇 |
2004年 | 108篇 |
2003年 | 88篇 |
2002年 | 95篇 |
2001年 | 75篇 |
2000年 | 90篇 |
1999年 | 57篇 |
1998年 | 37篇 |
1997年 | 36篇 |
1996年 | 24篇 |
1995年 | 39篇 |
1994年 | 24篇 |
1993年 | 28篇 |
1992年 | 17篇 |
1991年 | 12篇 |
1990年 | 12篇 |
1989年 | 14篇 |
1988年 | 7篇 |
1987年 | 16篇 |
1986年 | 10篇 |
1985年 | 7篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 17篇 |
1980年 | 13篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1975年 | 5篇 |
1972年 | 7篇 |
1971年 | 8篇 |
1970年 | 3篇 |
排序方式: 共有3621条查询结果,搜索用时 15 毫秒
251.
252.
Lawrence J. MacDonnell 《Journal of the American Water Resources Association》2009,45(5):1087-1099
Abstract: This paper provides an overview and summary of United States and Canadian federal, state, and provincial laws that offer some form of legal protection for environmental flows. Special attention is given to the new “second generation” law established in Texas and to ways western states are beginning to encourage transactions that help restore dewatered streams. Progress in the eastern states and some Canadian provinces to provide environmental flow protection is addressed. Based on this review, this paper presents recommended elements of a “model” environmental flow policy. 相似文献
253.
为研究出口单位流量与人流时间之间的关系,以某体育馆为例,进行对某一出口常态下的人流观测实验.通过理论计算和建立Cubic回归模型对采集数据进行了统计分析.发现:单位出口流量最大值为2人/(m·s),稳定值为0.8-1.2人/(m·s),最小值为0.2人/(m·s).出口单位流量是人流时间的三次函数.研究结果表明:出口单位流量是随着时间的变化而变化,不是一个定值,而且单位出口流量稳定值分布在初期.本文对性能化防火设计有一定的参考价值. 相似文献
254.
Land‐use dynamics and climatic gradients have large effects on many terrestrial systems. Exurban development, one of the fastest growing forms of land use in the United States, may affect wildlife through habitat fragmentation and building presence may alter habitat quality. We studied the effects of residential development and temperature gradients on bird species occurrence at 140 study sites in the southern Appalachian Mountains (North Carolina, U.S.A.) that varied with respect to building density and elevation. We used occupancy models to determine 36 bird species’ associations with building density, forest canopy cover, average daily mean temperature, and an interaction between building density and mean temperature. Responses varied with habitat requirement, breeding range, and migration distance. Building density and mean temperature were both included in the top occupancy models for 19 of 36 species and a building density by temperature interaction was included in models for 8 bird species. As exurban development expands in the southern Appalachians, interior forest species and Neotropical migrants are likely to decline, but shrubland or edge species are not likely to benefit. Overall, effects of building density were greater than those of forest canopy cover. Exurban development had a greater effect on birds at high elevations due to a greater abundance of sensitive forest‐interior species and Neotropical migrants. A warming climate may exacerbate these negative effects. Efectos del Desarrollo Exurbano y de la Temperatura sobre Especies de Aves en las Apalaches del Sur 相似文献
255.
K. M. S. Sundaram S. Y. Szeto 《Journal of environmental science and health. Part. B》2013,48(5):579-599
Abstract An oil‐based formulation of carbaryl (1‐naphthyl N‐methyl‐carbamate) (Sevin‐2‐Oil) was applied twice by a fixed‐wing aircraft at a dosage rate of 280 g of A.I./ha/application to a coniferous forest near Allardville, New Brunswick. The highest concentrations of the chemical in fir foliage, litter and forest soil 1 h after application were respectively 4.20, 1.21 and 0.59 ppm (fresh weight). The residues dissipated rapidly and the DT50 values obtained from the depletion curves were 2.3 d for foliage and 1.5 d for litter and soil samples. Very low levels (<0.1 ppm) of carbaryl persisted in foliage and litter beyond the 10 d sampling period. The maximum residue level found in stream water was 0.314 ppm and more than 50% of it had dissipated within 1 h. Low but detectable levels (0.001 ppm) of the chemical persisted in water until the end of the 10 d sampling period. Sediment samples contained a maximum level of 0.04 ppm, which dissipated below the detection limit within 5 h. Brook trout and slimy sculpins captured in the stream 1 d after the spray contained on average about 0.04 ppm of carbaryl and none of it was found in 3 d postspray samples. 相似文献
256.
257.
Richard L. Skaggs Larry W. Mays Lance W. Vail 《Journal of the American Water Resources Association》2001,37(4):867-875
ABSTRACT: A methodology for ground water remediation design has been developed that interfaces ground water simulation models with an enhanced annealing optimizer. The ground water flow and transport simulators provide the ability to consider site‐specific contamination and geohydrologic conditions directly in the assessment of alternative remediation system designs. The optimizer facilitates analysis of tradeoffs between technical, environmental, regulatory, and financial risks for alternative design and operation scenarios. A ground water management model using an optimization method referred to as “enhanced annealing” (simulated annealing enhanced to include “directional search” and “memory” mechanisms) has been developed and successfully applied to an actual restoration problem. The demonstration site is the contaminated unconfined aquifer referred to as N‐Springs located at Han‐ford, Washington. Results of the demonstration show the potential for improving groundwater restoration system performance while reducing overall system cost. 相似文献
258.
传统的U型通风工作面上隅角瓦斯积聚现象经常出现,严重制约着矿井正常生产能力的有效发挥,对矿井安全生产造成重大威胁。基于前人对采空区非均质多孔介质气体运移理论的研究,采用Fluent软件数值模拟研究了U型和上隅角埋管条件下U型通风系统的静压力场和瓦斯浓度场。研究结果表明:在相同的模型参数条件下,U型通风容易造成上隅角瓦斯积聚,上隅角瓦斯超限问题十分严重;采空区5m处埋管,治理上隅角瓦斯积聚的效果欠佳,达不到安全开采的条件;15m处埋管可以较好的解决上隅角瓦斯超限问题,工作面没有出现瓦斯积聚现象,工作面和回风巷的瓦斯浓度始终处于1%以下;25m处埋管的效果与15m基本相同,没有表现出更好的瓦斯治理效果。综合数值模拟的结果,确定了上隅角埋管抽放采空区瓦斯的理想抽放位置为距离地板垂高1.2m、沿走向深入采空区15m处。 相似文献
259.
ABSTRACT: A procedure of estimating instantaneous flood flows for various return periods on the Island of Newfoundland is presented. The procedure is based on annual maximum instantaneous flows rather than annual maximum daily-mean flows, as the latter requires the conversion of estimated daily-mean flows into instantaneous flows. Regression equations were developed for each of three homogeneous regions for the desired return periods. The flood flow estimation capability of the presented procedure is demonstrated to be better than any other currently available procedure on the Island. 相似文献
260.
采场是煤矿生产的核心地带,而采场通风系统是确保采场作业安全,创造良好生产环境的重要环节。本文以采场风流流动及瓦斯运移理论为基础,通过现场试验、模型模拟试验及计算机模拟研究等方法,着重研究了中国常用的和有发展前途的走向长壁后退式U型通风方式、U+L型通曲方式、后退式Y型通风方式条件下采场风流流动及瓦斯运移规律。 相似文献