全文获取类型
收费全文 | 1786篇 |
免费 | 138篇 |
国内免费 | 132篇 |
专业分类
安全科学 | 329篇 |
废物处理 | 31篇 |
环保管理 | 752篇 |
综合类 | 332篇 |
基础理论 | 285篇 |
污染及防治 | 163篇 |
评价与监测 | 91篇 |
社会与环境 | 37篇 |
灾害及防治 | 36篇 |
出版年
2024年 | 3篇 |
2023年 | 32篇 |
2022年 | 26篇 |
2021年 | 52篇 |
2020年 | 50篇 |
2019年 | 53篇 |
2018年 | 32篇 |
2017年 | 56篇 |
2016年 | 64篇 |
2015年 | 84篇 |
2014年 | 73篇 |
2013年 | 91篇 |
2012年 | 70篇 |
2011年 | 104篇 |
2010年 | 58篇 |
2009年 | 126篇 |
2008年 | 83篇 |
2007年 | 81篇 |
2006年 | 69篇 |
2005年 | 80篇 |
2004年 | 69篇 |
2003年 | 77篇 |
2002年 | 62篇 |
2001年 | 62篇 |
2000年 | 72篇 |
1999年 | 61篇 |
1998年 | 50篇 |
1997年 | 29篇 |
1996年 | 43篇 |
1995年 | 30篇 |
1994年 | 26篇 |
1993年 | 23篇 |
1992年 | 14篇 |
1991年 | 11篇 |
1990年 | 10篇 |
1989年 | 15篇 |
1988年 | 11篇 |
1987年 | 9篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 10篇 |
1981年 | 9篇 |
1980年 | 13篇 |
1979年 | 15篇 |
1978年 | 11篇 |
1977年 | 4篇 |
1974年 | 2篇 |
1970年 | 2篇 |
排序方式: 共有2056条查询结果,搜索用时 15 毫秒
931.
932.
为研究不同楼梯类型的行人疏散效果,改进传统社会力模型,模拟4种常见梯形中行人的疏散过程,并通过总疏散时间和平均疏散速度指标以及微观速度密度分布图分析其疏散效果中存在的内在物理机制。研究表明:从安全和高效疏散角度上看,在限定空间中,单跑无平台梯形布局有利于低密度人群下人员的快速疏散;在中、高密度人群中,双分梯形的分流特点更有利于人员安全、快速疏散。从微观密度、速度分布图可看到这4种梯形在人员疏散过程中均易造成人员聚集拥堵,但发生事故风险的位置不同。单跑有、无平台梯形在楼梯上端和下端均易发生拥堵,且此时速度值大,发生事故的风险高;双分与双跑梯形在楼梯与平台的转角处易发生拥堵。 相似文献
933.
Unmitigated anthropogenic climate change is set to exacerbate current stresses on water resources management and creates the need to develop strategies to face climate change impacts on water resources, especially in the long term. Insufficient information on possible impacts on water availability limits the organization and promotion of efforts to adapt and improve the resilience and efficiency of water systems. To document the potential impacts of climate change in the region of Mendoza, Argentina, we perform a hydrological modeling of the Mendoza River watershed using a SWAT model and project climate change scenarios to observe hydrological changes. The results show the impact of higher temperature on glaciers as river flow increases due to glacier melting; at the same time, runoff decreases as precipitation is reduced. Furthermore, the runoff timing is shifted and an earlier melting becomes more important in more pronounced climate change scenarios. Scenarios show a reduction in water availability that ranges between 1 and 10%. An additional scenario under stronger climate change conditions without glaciers data shows a reduction of the river flow by up to 11.8%. This scenario would correspond to a future situation in which glaciers have completely melted. These situations would imply a reduction in the water availability and the possibility of future unsatisfied water uses, in particular for irrigation, which received most of the available water in Mendoza, on which agricultural activities and regional economy depends. 相似文献
934.
M.S. Srinivasan Pierre Grard‐Marchant Tamie L. Veith William J. Gburek Tammo S. Steenhuis 《Journal of the American Water Resources Association》2005,41(2):361-377
ABSTRACT: A curve number based model, Soil and Water Assessment Tool (SWAT), and a physically based model, Soil Moisture Distribution and Routing (SMDR), were applied in a headwater watershed in Pennsylvania to identify runoff generation areas, as runoff areas have been shown to be critical for phosphorus management. SWAT performed better than SMDR in simulating daily streamflows over the four‐year simulation period (Nash‐Sutcliffe coefficient: SWAT, 0.62; SMDR, 0.33). Both models varied streamflow simulations seasonally as precipitation and watershed conditions varied. However, levels of agreement between simulated and observed flows were not consistent over seasons. SMDR, a variable source area based model, needs further improvement in model formulations to simulate large peak flows as observed. SWAT simulations matched the majority of observed peak flow events. SMDR overpredicted annual flow volumes, while SWAT underpredicted the same. Neither model routes runoff over the landscape to water bodies, which is critical to surface transport of phosphorus. SMDR representation of the watershed as grids may allow targeted management of phosphorus sources. SWAT representation of fields as hydrologic response units (HRUs) does not allow such targeted management. 相似文献
935.
Abstract The Foliar Washoff of Pesticides (FWOP) Model was developed to provide an empirical simulation of pesticide washoff from plant leaf surfaces as influenced by rainfall amount. To evaluate the technique, simulations by the FWOP Model were compared to those by the foliar washoff algorithm of the Chemical, Runoff and Erosion from Agricultural Management Systems (CREAMS) Model. The two algorithms were linked individually to the Pesticide Runoff Simulator (PRS) for the comparison. Five years of test data from a Mississippi watershed were used to evaluate six insecticides (carbaryl, profenofos, methyl parathion, permethrin, phorate, and toxaphene). Initially, the FWOP model was used to evaluate the relative impact of chemical distribution (foliage versus soil) on the subsequent foliar washoff and soil surface contributions to runoff losses. Results indicated that runoff losses were low If all of the insecticide was applied to the foliage whereas high losses occurred if applied only to the soil. When an assumed application was distributed between the plant and soil (i.e., 90% to foliage and 10% to soil), predicted runoff losses compared well with observed field data (<3% of the application rate). Except for toxaphene, the FWOP model generally predicted less washoff and subsequent runoff losses than the CREAMS approach. Simulated toxaphene washoff losses were in good agreement with observed field data. Statistical comparisons of the two modeling approaches using the Kolmogorov‐Smirnov test showed differences in the two cumulative frequency distributions for washoff but smaller differences for runoff. Average 5‐year runoff losses, however, were greater using the CREAMS approach—by factors of 2, 3, and 3 for profenofos, methyl parathion and phorate, respectively. Results from this study will be useful for upgrading current exposure assessment models to more accurately address foliar washoff losses of pesticides as well as for assessing the impact of foliar‐applied chemicals on environmental quality. 相似文献
936.
Structural equation modeling (SEM) holds the promise of providing natural scientists the capacity to evaluate complex multivariate
hypotheses about ecological systems. Building on its predecessors, path analysis and factor analysis, SEM allows for the incorporation
of both observed and unobserved (latent) variables into theoretically-based probabilistic models. In this paper we discuss
the interface between theory and data in SEM and the use of an additional variable type, the composite. In simple terms, composite
variables specify the influences of collections of other variables and can be helpful in modeling heterogeneous concepts of
the sort commonly of interest to ecologists. While long recognized as a potentially important element of SEM, composite variables
have received very limited use, in part because of a lack of theoretical consideration, but also because of difficulties that
arise in parameter estimation when using conventional solution procedures. In this paper we present a framework for discussing
composites and demonstrate how the use of partially-reduced-form models can help to overcome some of the parameter estimation
and evaluation problems associated with models containing composites. Diagnostic procedures for evaluating the most appropriate
and effective use of composites are illustrated with an example from the ecological literature. It is argued that an ability
to incorporate composite variables into structural equation models may be particularly valuable in the study of natural systems,
where concepts are frequently multifaceted and the influence of suites of variables are often of interest. 相似文献
937.
DARREN M. SOUTHWELL ALEX M. LECHNER† TERRY COATES‡ BRENDAN A. WINTLE§ 《Conservation biology》2008,22(4):1045-1054
Abstract: Whenever population viability analysis (PVA) models are built to help guide decisions about the management of rare and threatened species, an important component of model building is the specification of a habitat model describing how a species is related to landscape or bioclimatic variables. Model-selection uncertainty may arise because there is often a great deal of ambiguity about which habitat model structure best approximates the true underlying biological processes. The standard approach to incorporate habitat models into PVA is to assume the best habitat model is correct, ignoring habitat-model uncertainty and alternative model structures that may lead to quantitatively different conclusions and management recommendations. Here we provide the first detailed examination of the influence of habitat-model uncertainty on the ranking of management scenarios from a PVA model. We evaluated and ranked 6 management scenarios for the endangered southern brown bandicoot ( Isoodon obesulus ) with PVA models, each derived from plausible competing habitat models developed with logistic regression. The ranking of management scenarios was sensitive to the choice of the habitat model used in PVA predictions. Our results demonstrate the need to incorporate methods into PVA that better account for model uncertainty and highlight the sensitivity of PVA to decisions made during model building. We recommend that researchers search for and consider a range of habitat models when undertaking model-based decision making and suggest that routine sensitivity analyses should be expanded to include an analysis of the impact of habitat-model uncertainty and assumptions. 相似文献
938.
Darío A. Maggioni Marcelo L. Signorini Nicolás Michlig María R. Repetti Mirna E. Sigrist 《Journal of environmental science and health. Part. B》2013,48(10):639-651
ABSTRACTAn evaluation of acute dietary exposure to pesticide residues, applying deterministic and stochastic methods, was performed for a selected group of pesticides in two representative age groups from Argentina. Thus, 28 active ingredients (a.i.) and 75 food items were evaluated for the group of 2–5-year-old children, while 9 a.i. and 59 food items were considered for the 10–49-year-old women group. A deterministic assessment was conducting following the Food and Agriculture Organization (FAO) and World Health Organization (WHO) procedure but using the national maximum residue limits (MRLs) as pesticide residue concentration data, while in the stochastic approach, a theoretical distribution modeled with the available information was used. Food consumption data were obtained from the 2004–2005 comprehensive national nutrition and health survey. The risk was estimated by comparing the short-term dietary exposure with the acute reference dose (ARfD) values for each pesticide-food combination evaluated. In the deterministic assessment, 173 (39.1%) and 40 (31.3%) combinations exceeded the ARfD thresholds for the 2–5-year-old children and 10–49-year-old women groups, respectively. This conservative study generated relevant information as a first stage of acute dietary risk assessment in Argentina. 相似文献
939.
Richard N. Palmer Hal E. Cardwell Mark A. Lorie William Werick 《Journal of the American Water Resources Association》2013,49(3):614-628
Participatory planning applied to water resources has sparked significant interest and debate during the last decade. Recognition that models play a significant role in the formulation and implementation of design and management strategies has encouraged the profession to consider how such models can be best implemented. Shared Vision Planning (SVP) is a disciplined planning approach that combines traditional water resources planning methodologies with innovations such as structured public participation and the use of collaborative modeling, resulting in a more complete understanding and an integrative decision support tool. This study reviews these three basic components of SVP and explains how they are incorporated into a unified planning approach. The successful application of SVP is explored in three studies involving planning challenges: the National Drought Study, the Lake Ontario‐St. Lawrence River Study, and the Apalachicola‐Chattahoochee‐Flint/Alabama‐Coosa‐Tallapoosa River Basin Study. The article concludes by summarizing the advantages and limitations of this planning approach. 相似文献
940.
As the world pays more attention to low-earbon and sustainable development,there’s a growing trend in architecture,engineering and construction fields to construct greener,more energy efficient and more sustainable buildings with the help of building information modeling(BIM).As BIM application becomes popular in industry,more and more scholars and engineers point out that an integrated construction environment is better for BIM’s fully functional capability.This paper illustrates the relationship between BIM application and an integrated construction environment based on case survey data.It is found that even though an integration construction environment is not necessary in BIM application,the statistical results showed that DBB(design-bid-build)and CM(construction management)modes have great differences in BIM’s application implementation scope and implementation deepness,while DB and CM modes do not. 相似文献