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   3479篇
  免费   86篇
  国内免费   41篇
安全科学   172篇
废物处理   144篇
环保管理   923篇
综合类   316篇
基础理论   810篇
环境理论   4篇
污染及防治   850篇
评价与监测   225篇
社会与环境   135篇
灾害及防治   27篇
  2023年   19篇
  2022年   24篇
  2021年   38篇
  2020年   40篇
  2019年   47篇
  2018年   66篇
  2017年   72篇
  2016年   117篇
  2015年   72篇
  2014年   90篇
  2013年   397篇
  2012年   119篇
  2011年   188篇
  2010年   148篇
  2009年   158篇
  2008年   166篇
  2007年   184篇
  2006年   150篇
  2005年   97篇
  2004年   125篇
  2003年   130篇
  2002年   112篇
  2001年   63篇
  2000年   58篇
  1999年   52篇
  1998年   44篇
  1997年   42篇
  1996年   53篇
  1995年   62篇
  1994年   54篇
  1993年   45篇
  1992年   33篇
  1991年   35篇
  1990年   37篇
  1989年   26篇
  1988年   36篇
  1987年   31篇
  1986年   42篇
  1985年   28篇
  1984年   46篇
  1983年   33篇
  1982年   37篇
  1981年   39篇
  1980年   25篇
  1979年   23篇
  1978年   17篇
  1977年   14篇
  1976年   12篇
  1974年   11篇
  1972年   10篇
排序方式: 共有3606条查询结果,搜索用时 31 毫秒
81.
Nature-based solutions (NBS) find increasing attention as actions to address societal challenges through harnessing ecological processes, yet knowledge gaps exist regarding approaches to landscape planning with NBS. This paper aims to provide suggestions of how planning NBS can be conceptualized and applied in practice. We develop a framework for planning NBS by merging insights from literature and a case study in the Lahn river landscape, Germany. Our framework relates to three key criteria that define NBS, and consists of six steps of planning: Co-define setting, Understand challenges, Create visions and scenarios, Assess potential impacts, Develop solution strategies, and Realize and monitor. Its implementation is guided by five principles, namely Place-specificity, Evidence base, Integration, Equity, and Transdisciplinarity. Drawing on the empirical insights from the case study, we suggest suitable methods and a checklist of supportive procedures for applying the framework in practice. Taken together, our framework can facilitate planning NBS and provides further steps towards mainstreaming.Electronic supplementary materialThe online version of this article (10.1007/s13280-020-01365-1) contains supplementary material, which is available to authorized users.  相似文献   
82.
Environmental Science and Pollution Research - Bio-waste materials from aquatic species are alternative sources of chitin and chitosan—high-value natural biodegradable and biocompatible...  相似文献   
83.
84.
85.
Climate change and sea level rise (SLR) pose risks to coastal communities around the world, but societal understanding of the distributional and equity implications of SLR impacts and adaptation actions remains limited. Here, we apply a new analytic tool to identify geographic areas in the contiguous United States that may be more likely to experience disproportionate impacts of SLR, and to determine if and where socially vulnerable populations would bear disproportionate costs of adaptation. We use the Social Vulnerability Index (SoVI) to identify socially vulnerable coastal communities, and combine this with output from a SLR coastal property model that evaluates threats of inundation and the economic efficiency of adaptation approaches to respond to those threats. Results show that under the mid-SLR scenario (66.9 cm by 2100), approximately 1,630,000 people are potentially affected by SLR. Of these, 332,000 (~20%) are among the most socially vulnerable. The analysis also finds that areas of higher social vulnerability are much more likely to be abandoned than protected in response to SLR. This finding is particularly true in the Gulf region of the United States, where over 99% of the most socially vulnerable people live in areas unlikely to be protected from inundation, in stark contrast to the least socially vulnerable group, where only 8% live in areas unlikely to be protected. Our results demonstrate the importance of considering the equity and environmental justice implications of SLR in climate change policy analysis and coastal adaptation planning.  相似文献   
86.
Algae biomass is an attractive biofuel feedstock when grown with high productivity on marginal land. Hydrothermal liquefaction (HTL) produces more oil from algae than lipid extraction (LE) does because protein and carbohydrates are converted, in part, to oil. Since nitrogen in the algae biomass is incorporated into the HTL oil, and since lipid extracted algae for generating heat and electricity are not co-produced by HTL, there are questions regarding implications for emissions and energy use. We studied the HTL and LE pathways for renewable diesel (RD) production by modeling all essential operations from nutrient manufacturing through fuel use. Our objective was to identify the key relationships affecting HTL energy consumption and emissions. LE, with identical upstream growth model and consistent hydroprocessing model, served as reference. HTL used 1.8 fold less algae than did LE but required 5.2 times more ammonia when nitrogen incorporated in the HTL oil was treated as lost. HTL RD had life cycle emissions of 31,000 gCO2 equivalent (gCO2e) compared to 21,500 gCO2e for LE based RD per million BTU of RD produced. Greenhouse gas (GHG) emissions increased when yields exceeded 0.4 g HTL oil/g algae because insufficient carbon was left for biogas generation. Key variables in the analysis were the HTL oil yield, the hydrogen demand during upgrading, and the nitrogen content of the HTL oil. Future work requires better data for upgrading renewable oils to RD and requires consideration of nitrogen recycling during upgrading.  相似文献   
87.
The application of controlled, low-frequency modulation (~100 Hz) superimposed onto the cutting process in the feed-direction – modulation-assisted machining (MAM) – is shown to be quite effective in reducing the wear of cubic boron nitride (CBN) tools when machining compacted graphite iron (CGI) at high machining speeds (>500 m/min). The tool life is at least 20 times greater than in conventional machining. This significant reduction in wear is a consequence of the multiple effects realized by MAM, including periodic disruption of the tool–workpiece contact, formation of discrete chips, enhanced fluid action and lower cutting temperatures. The propensity for thermochemical wear of CBN, the principal wear mode at high speeds in CGI machining, is thus reduced. The tool wear in MAM is also found to be smaller at the higher cutting speeds (730 m/min) tested. The feed-direction MAM appears feasible for implementation in industrial machining applications involving high speeds.  相似文献   
88.
(E)-6,10-dimethyl-5,9-undecadien-2-ol (geranyl acetol), termed here fuscol, was identified as a male-produced pheromone emitted by Tetropium fuscum (F.) and Tetropium cinnamopterum Kirby. In field experiments, traps baited with synthetic fuscol alone were not significantly attractive, but the combination of fuscol plus host volatiles (a synthetic blend of monoterpenes plus ethanol) attracted significantly more male and female T. fuscum and female T. cinnamopterum than did host volatiles alone. This is the first homoterpenoid alcohol to be described in the Cerambycidae, and the first pheromone reported from the sub-family Spondylidinae.  相似文献   
89.
OBJECTIVE: Vehicular speeds have been identified to be at the core of road accident severity and frequency globally. Whereas speed control is a fundamental priority and the cornerstone of road safety in the developed world, the subject is at rudimentary stages in most developing countries thus making research into vehicle speeds in developing nations imperative. The main aim of the study was to establish two major speed parameters, namely the mean speed and dispersion, and their implications for more extensive and long-term speed monitoring in Ghana. METHODS: Research workers stationed themselves in a parked car and used a radar gun to unobtrusively measure the travelling speeds of 4,163 vehicles over two 24-hour periods at two separate sites on one of the main inter-urban roads (Accra-Kumasi). Both sites were settled areas with posted speed limits of 50 km/hr. RESULTS: Over 95% of vehicles travelled above the posted speed limit of 50 km/hr. Vehicles on an average travelled at 87 km/hr, (95% CI=87, 88). Variation in speeds was wide, with a standard deviation of 18 km/hr for all classes of vehicles, and with a range of 40 to 187 km/hr. The highest vehicular speed was associated with the private car (97.6+/-18.3 km/hr) followed by large buses (93.6+/-13.3 km/hr) and the least was with heavy trucks (73.8+/-12.9 km/hr). CONCLUSION: The excessive vehicular speeds coupled with the wide speed variations explain in part the high incidence of traffic crashes and fatalities on the Accra-Kumasi highway. An integrated speed monitoring and control program, and realigning the highway to by-pass small and medium settlements would be required as a long-term measure for the reduction of speed-related road traffic crashes, fatalities, and injuries in Ghana.  相似文献   
90.
We report that the abdominal epidermis and associated tissues are the predominant sources of male-produced pheromones in the red flour beetle, Tribolium castaneum and, for the first time, describe the stereoisomeric composition of the natural blend of isomers of the aggregation pheromone 4,8-dimethyldecanal (DMD) in this important pest species. Quantitative analyses via gas chromatography–mass spectrometry showed that the average amount of DMD released daily by single feeding males of T. castaneum was 878 ± 72 ng (SE). Analysis of different body parts identified the abdominal epidermis as the major source of aggregation pheromone; the thorax was a minor source, while no DMD was detectable in the head. No internal organs or obvious male-specific glands were associated with pheromone deposition. Complete separation of all four stereoisomers of DMD was achieved following oxidation to the corresponding acid, derivatization with (1R, 2R)- and (1S, 2S)-2-(anthracene-2,3-dicarboximido)cyclohexanol to diastereomeric esters, and their separation on reversed-phase high-performance liquid chromatography at −54°C. Analysis of the hexane eluate from Porapak-Q-collected volatiles from feeding males revealed the presence of all four isomers (4R,8R)/(4R,8S)/(4S,8R)/(4S,8S) at a ratio of approximately 4:4:1:1. A walking orientation bioassay in a wind tunnel with various blends of the four synthetic isomers further indicated that the attractive potency of the reconstituted natural blend of 4:4:1:1 was equivalent to that of the natural pheromone and greater than that of the 1:1 blend of (4R,8R)/(4R,8S) used in commercial lures.  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