首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2582篇
  免费   236篇
  国内免费   576篇
安全科学   423篇
废物处理   90篇
环保管理   542篇
综合类   1247篇
基础理论   291篇
污染及防治   356篇
评价与监测   103篇
社会与环境   116篇
灾害及防治   226篇
  2024年   7篇
  2023年   27篇
  2022年   62篇
  2021年   81篇
  2020年   95篇
  2019年   68篇
  2018年   67篇
  2017年   98篇
  2016年   123篇
  2015年   145篇
  2014年   152篇
  2013年   189篇
  2012年   200篇
  2011年   209篇
  2010年   174篇
  2009年   171篇
  2008年   129篇
  2007年   168篇
  2006年   174篇
  2005年   140篇
  2004年   101篇
  2003年   101篇
  2002年   92篇
  2001年   91篇
  2000年   96篇
  1999年   51篇
  1998年   35篇
  1997年   39篇
  1996年   23篇
  1995年   47篇
  1994年   23篇
  1993年   30篇
  1992年   19篇
  1991年   13篇
  1990年   16篇
  1989年   13篇
  1988年   9篇
  1987年   15篇
  1986年   11篇
  1985年   9篇
  1983年   5篇
  1982年   6篇
  1981年   11篇
  1980年   12篇
  1979年   7篇
  1978年   7篇
  1973年   3篇
  1972年   7篇
  1971年   9篇
  1970年   3篇
排序方式: 共有3394条查询结果,搜索用时 703 毫秒
701.
ABSTRACT: A study was conducted over a six-year period in East-Central Ohio to determine the effects of surface mining and reclamation on physical watershed conditions and on ground-water hydrology in three ground-water zones in three small experimental watersheds. Mining disturbances in watersheds adjacent to the experimental sites affected ground-water levels in the undisturbed experimental watersheds prior to actual mining in the experimental sites. New subsurface flow paths, with different characteristics, formed during mining and reclamation. At all three sites mining dewatered the saturated zone above the underclay of the mined coal seam. Mining and reclamation affected ground-water levels below the mined coal seam in the middle and lower zones within at least two sites. Ground-water level recovery in the mined upper saturated zone was slow and irregular both temporally and spatially after reclamation. Hydraulic conductivities of postmining (Phase 3) spoil were generally greater than those of Phase 1 bedrock, but wide spatial variability was observed. Modelers need to be aware of the complexities of new flow paths and physical characteristics of subsurface flow media that are introduced by mining and reclamation, including destruction of the upper-zone clay.  相似文献   
702.
ABSTRACT: The ability to predict extreme floods is an important part of the planning process for any water project for which failure will be very costly. The length of a gage record available for use in estimating extreme flows is generally much shorter than the recurrence interval of the desired flows, resulting in estimates having a high degree of uncertainty. Maximum likelihood estimators of the parameters of the three parameter lognormal (3PLN) distribution, which make use of historical data, are presented. A Monte Carlo study of extreme flows estimated from samples drawn from three hypothetical 3PLN populations showed that inclusion of historical flows with the gage record reduced the bias and variance of extreme flow estimates. Asymptotic theory approximations of parameter variances and covariances calculated using the second and mixed partial derivatives of the log likelihood function agreed well with Monte Carlo results. First order approximations of the standard deviations of the extreme flow estimates did not agree with the Monte Carlo results. An alternative method for calculating those standard deviations, the “asymptotic simulation” method, is described. The standard deviations calculated by asymptotic simulation agree well with the Monte Carlo results.  相似文献   
703.
ABSTRACT: Waddell Creek is a perennial stream near Santa Cruz, California, which discharges into the Pacific Ocean about 38 km from the epicenter of the Loma Prieta earthquake (October 17, 1989, M 7.1). The earthquake caused no significant changes or damage to structures or surface features in the area, but was followed by an order of magnitude transient increase in discharge of Waddell Creek and nearby springs. The transients approximate a step rise followed by an exponential recession with time constants of from 37 to 59 days. The flow recession pattern of Waddell Creek was obscured by heavy rains after about 50 days; however, the springs maintained an exponential recession with minimal rain interference for periods of several time constants, then abruptly ceased flowing. A comparison of the pre-quake and post-quake chemical signature of one of the springs shows only minor changes in water chemistry indicating a common source for pre- and post-quake waters. Increased permeability of the subsurface ground material appears to be the most probable cause of the hydrologic changes. Post-seismic reduction of permeability has not been observed or inferred.  相似文献   
704.
ABSTRACT: A drain function and set of type curves were defined for the mathematical solution that represents one-dimensional flow under nonsteady conditions in a leaky aquifer for the constant drawdown boundary condition. A match point procedure was developed for determining the aquifer parameters transmissivity, storage coefficient, and leakance based on the drain function and type curves. Use of the procedure is illustrated by an example that utilizes simulated aquifer drawdowns and flowrate data. The drain function and type curves developed in this investigation include the effects of leakage for the constant drawdown boundary condition, which is not included in the existing drain function and type curve found in the literature. Thus, a new set of type curves was developed that can be used to analyze drawdowns for one-dimensional flow in a leaky aquifer with constant drawdown at a line sink. Applications would include flow to a canal or river, drainage of agricultural lands, and dewatering associated with strip mining operations.  相似文献   
705.
ABSTRACT: There is a growing literature on the resolution of natural resources conflicts. Much of it is practical, focusing on guidelines for hands-on negotiation. This literature can be a guide in water conflicts. This is especially true for negotiations over new environmental values such as instream flow. The concepts of competitive, cooperative, and integrative styles of conflict resolution are applied to three cases of water resource bargaining. Lessons for the effective use of these ideas include: break a large number of parties into small working groups, approach value differences in small steps, be cautious in the presence of an attentive public, keep decisions at the local level, and understand the opponent's interests.  相似文献   
706.
固体废物管理技术进展   总被引:2,自引:1,他引:2  
概述了固体废物管理技术近年来的主要进展,这些进展包括,固体废物从“摇蓝到坟墓”的全过程管理,即从废物产生到收集、运输贮存,再循环,再利用,处理直至最终处理过程所涉及到的:废物最小量化管理技术;废物转移跟踪管理中产生者,运输者,处理处理者,主管当局的职责、主管当局的职责,义务和管理方式;废物经营者向主管当局申请许可证的程序和申请。时,对废物交换制度和废物管理信息系统也作了概要介绍。  相似文献   
707.
串联式氨解脱离子交换法处理味精等电点废母液   总被引:2,自引:0,他引:2  
李丽  顾晓彬 《环境工程》1998,16(1):7-10
提出了一种味精生产污染物控制新技术。采用四只串联的离子交换柱连续、交替吸附味精生产等电点废母液中残留的谷氨酸,通氨洗脱树脂吸附的谷氨酸,回收谷氨酸生产味精。这一技术可使味精得率提高45%,污染物CODCr排放量减少256%。  相似文献   
708.
Diagenesis of Upper Carboniferous foreland shelf rocks in southeastern Kansas took place at temperatures as high as 100–150° C at a depth of less than 2 km. High temperatures are the result of the long distance (hundreds of kilometers) advection of groundwater related to collisional orogeny in the Ouachita tectonic belt to the south. Orogenic activity in the Ouachita area was broadly Late Carboniferous, equivalent to the Variscan activity of Europe. Mississippi Valley-type Pb-Zn deposits and oil and gas fields in the US midcontinent and elsewhere are commonly attributed to regional groundwater flow resulting from such collisional events. This paper describes the diagenesis and thermal effects in sandstone and limestone of Upper Carboniferous siliciclastic and limestone-shale cyclothems, the purported confining layer of a supposed regional aquifer. Diagenesis took place in early, intermediate, and late stages. Many intermediate and late stage events in the sandstones have equivalents in the limestones, suggesting that the causes were regional. The sandstone paragenesis includes siderite cement (early stage), quartz overgrowths (intermediate stage), dissolution of feldspar and carbonates, followed by minor Fe calcite, pore-filling kaolinite and sub-poikilotopic Ca ankerite (late stage). The limestone paragenesis includes calcite cement (early stage); megaquartz, chalcedony, and Fe calcite spar (intermediate stage); and dissolution, Ca-Fe dolomite and kaolinite (late stage). The R m value of vitrinite shows a regional average of 0.6–0.7%; Rock-Eval T maX suggests a comparable degree of organic maturity. The T h of aqueous fluid inclusions in late stage Ca-Fe-Mg carbonates ranges from 90 to 160° and T mice indicates very saline water (>200000 ppm NaCl equivalent); 18O suggests that the water is of basinal origin. Local warm spots have higher R m, T max, and T h. The results constrain numerical models of regional fluid migration, which is widely viewed as an artesian flow from recharge areas in the Ouachita belt across the foreland basin onto the foreland shelf area. Such models must account for heating effects that extend at least 500 km from the orogenic front and affect both supposed aquifer beds and the overlying supposed confining layer. Warm spots indicate either more rapid or more prolonged flow locally. T h and T mice data show the highest temperatures coincided with high salinity fluids.  相似文献   
709.
混凝气浮-推流式活性污泥-深度处理法处理染色废水   总被引:2,自引:1,他引:2  
介绍了混凝气浮-推流式活性污泥-深度处理法在染色废水工程中的应用,分析了工程的设计及运行的情况。实践表明,混凝气浮预处理可以有效去除色度、悬浮物和部分有机物,提高抗冲击负荷能力;推流式活性污泥法有较高的处理效率,经深度处理后,废水达标排放。  相似文献   
710.
连续流间歇曝气工艺的氮磷脱除功能研究   总被引:4,自引:0,他引:4  
连续流间歇曝气工艺是在对传统活性污泥法的改造中发展起来的一种工艺。本文针对该工艺的氮磷脱除功能进行了小试研究 ,由试验结果可看出 ,连续流间歇曝气工艺简便易行 ,去除有机物及氨氮的效果稳定 ,在碳源满足脱氮除磷要求的条件下 ,可达到良好的氮磷脱除效果  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号