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   747篇
  免费   52篇
  国内免费   219篇
安全科学   50篇
废物处理   10篇
环保管理   53篇
综合类   396篇
基础理论   211篇
污染及防治   194篇
评价与监测   44篇
社会与环境   38篇
灾害及防治   22篇
  2024年   1篇
  2023年   6篇
  2022年   11篇
  2021年   17篇
  2020年   25篇
  2019年   29篇
  2018年   15篇
  2017年   20篇
  2016年   36篇
  2015年   34篇
  2014年   38篇
  2013年   91篇
  2012年   83篇
  2011年   87篇
  2010年   42篇
  2009年   73篇
  2008年   42篇
  2007年   50篇
  2006年   44篇
  2005年   35篇
  2004年   35篇
  2003年   27篇
  2002年   29篇
  2001年   29篇
  2000年   26篇
  1999年   18篇
  1998年   7篇
  1997年   19篇
  1996年   12篇
  1995年   8篇
  1994年   4篇
  1993年   7篇
  1992年   3篇
  1991年   9篇
  1990年   1篇
  1988年   1篇
  1985年   1篇
  1982年   1篇
  1978年   2篇
排序方式: 共有1018条查询结果,搜索用时 140 毫秒
1.
Unsustainable wildlife trade affects biodiversity and the livelihoods of communities dependent upon those resources. Wildlife farming has been proposed to promote sustainable trade, but characterizing markets and understanding consumer behavior remain neglected but essential steps in the design and evaluation of such operations. We used sea turtle trade in the Cayman Islands, where turtles have been farm raised for human consumption for almost 50 years, as a case study to explore consumer preferences toward wild‐sourced (illegal) and farmed (legal) products and potential conservation implications. Combining methods innovatively (including indirect questioning and choice experiments), we conducted a nationwide trade assessment through in‐person interviews from September to December 2014. Households were randomly selected using disproportionate stratified sampling, and responses were weighted based on district population size. We approached 597 individuals, of which 37 (6.2%) refused to participate. Although 30% of households had consumed turtle in the previous 12 months, the purchase and consumption of wild products was rare (e.g., 64–742 resident households consumed wild turtle meat [i.e., 0.3–3.5% of households] but represented a large threat to wild turtles in the area due to their reduced populations). Differences among groups of consumers were marked, as identified through choice experiments, and price and source of product played important roles in their decisions. Despite the long‐term practice of farming turtles, 13.5% of consumers showed a strong preference for wild products, which demonstrates the limitations of wildlife farming as a single tool for sustainable wildlife trade. By using a combination of indirect questioning, choice experiments, and sales data to investigate demand for wildlife products, we obtained insights about consumer behavior that can be used to develop conservation‐demand‐focused initiatives. Lack of data from long‐term social–ecological assessments hinders the evaluation of and learning from wildlife farming. This information is key to understanding under which conditions different interventions (e.g., bans, wildlife farming, social marketing) are likely to succeed.  相似文献   
2.
基于中国绿洲喜凉作物(chimonophilous crop)分布区39个站点1960~2016年逐日平均气温资料,运用线性趋势法、反距离加权插值(IDW)、Morlet小波、Mann-Kendall检验等方法,研究中国绿洲喜凉作物气候生长期的时空变化对变暖停滞的响应.结果表明:①变暖停滞期,中国绿洲喜凉作物气候生长期起、止日及生长期日数以-0.2d/10a、0.33d/10a、0.53d/10a的趋势变化,较1960~2016年起始日提前趋势减缓1.01d/10a,终止日推迟减缓1.28d/10a,生长期日数延长减缓2.3d/10a,对变暖停滞有响应.②中国绿洲喜凉作物气候生长期起始日对变暖停滞响应的站点有44%,终止日和生长期日数均为49%,主要分布在南疆、柴达木盆地和河西绿洲,其中河西绿洲对变暖停滞响应最明显,南疆次之,柴达木最小,而北疆绿洲不存在滞缓现象,显然空间差异明显.③M-K检验显示,中国绿洲喜凉作物气候生长期起、止日及生长期日数分别在2001年、1990年和1997年发生突变,起始日晚于变暖停滞起始年份,终止日和生长期日数早于变暖停滞起始年,且分绿洲生长期日数突变年与变暖停滞起始年相接近.④Morlet小波得出变暖停滞期其变化稳定存在2.4~4.3a的震荡周期,表明未来几年中国绿洲喜凉作物气候生长期仍持续延长.  相似文献   
3.
为探究孕激素左炔诺孕酮(LNG)对鱼类脂质代谢的影响,将刚孵化的稀有鮈鲫仔鱼置于0.8和6.5ng/L LNG暴露6个月至性成熟,考察其生长指标、肝脏组织病理学变化、脂质和脂蛋白含量及脂质代谢相关基因的表达情况.结果显示:(1)0.8,6.5ng/L LNG暴露显著降低70dph稀有鮈鲫的体重和肥满度,且6.5ng/L LNG暴露显著降低180dph雌、雄鱼的体长或体重;(2)0.8,6.5ng/L LNG暴露导致180dph成鱼肝脏出现细胞空泡、肝细胞肿胀等损伤;(3)0.8,6.5ng/L LNG暴露显著降低180dph雌鱼肝脏中甘油三酯、胆固醇的含量,且6.5ng/L LNG暴露显著降低雌鱼血浆中甘油三酯的含量,但对雄鱼肝脏及血浆的脂质含量无显著影响;(4)0.8,6.5ng/L LNG暴露显著降低180dph雌鱼肝脏中脂肪酸合成酶基因(fasn) mRNA的表达水平,且6.5ng/L LNG暴露显著降低180dph雄鱼肝脏中fasn及乙酰辅酶A羧化酶基因(acaca) mRNA的表达水平.由此可见,LNG长期低剂量暴露可抑制稀有鮈鲫的生长、诱导肝细胞损伤、引起肝脏和血浆脂质含量发生性别差异性变化,并影响肝脏中脂质代谢相关基因的表达,表明LNG在低浓度下可干扰稀有鮈鲫的脂质代谢,提示LNG对鱼类种群具有较高的潜在生态风险.  相似文献   
4.
Based on density functional theory (DFT) and basic structure models, the chemical reactions on the surface of vanadium-titanium based selective catalytic reduction (SCR) denitrification catalysts were summarized. Reasonable structural models (non-periodic and periodic structural models) are the basis of density functional calculations. A periodic structure model was more appropriate to represent the catalyst surface, and its theoretical calculation results were more comparable with the experimental results than a non-periodic model. It is generally believed that the SCR mechanism where NH3 and NO react to produce N2 and H2O follows an Eley-Rideal type mechanism. NH2NO was found to be an important intermediate in the SCR reaction, with multiple production routes. Simultaneously, the effects of H2O, SO2 and metal on SCR catalysts were also summarized.  相似文献   
5.
From 2000 to 2010 China experienced rapid economic development and urbanization. Many cities in economically developed areas have developed from a single-center status to polycentricity. In this study, we used exploratory spatial data analysis (ESDA) to identify the population centers, which identified 232 cities in China as having urban centers. COMP was used to represent urban agglomeration, and POLYD (representing how far is the city's sub-centers to the main center), POLYC (representing the number of a city's centers), and POLYP (representing the population distributed between the main center and the sub-centers) were used to indicate urban polycentricity. Night light data were used to determine the CO2 emissions from various cities in China. A mixed model was used to study the impact of urban aggregation and polycentric data on the CO2 emission efficiency in 2000 and 2010. The study found that cities with higher compactness were distributed in coastal areas, and the cities with higher multicentricity were distributed in the Yangtze River Delta and Shandong Province. The more compact the city was, the less conducive it was to improving CO2 emission efficiency. Polycentric development of the city was conducive to improving the CO2 emission efficiency, but the number of urban centers had no significant relationship with the CO2 emission efficiency. Our research showed that the compactness and multicentricity of the city had an impact on the CO2 emission efficiency and provided some planning suggestions for the low carbon development of the city.  相似文献   
6.
In South Carolina, U.S.A., mink have been reintroduced from two apparently healthy populations to areas where populations haveexisted in the past but have been extirpated. High mortality wasobserved during transport of mink from the source populations. Inorder to elucidate the potential effects of dioxin-like compoundson the survival and reproduction of mink, concentrations of totalpolychlorinated biphenyls (PCBs), p,p-DDE, dioxin-likePCBs, polychlorinated dibenzo-p-dioxins (PCDDs), anddibenzofurans (PCDFs) were measured in livers of mink collectedfrom the source populations in South Carolina and Louisiana. Concentrations of total 2,3,7,8-tetrachlorodibenzo-p-dioxinequivalents (TEQs) for the South Carolina and Louisiana mink were21 and 14 pg g-1, wet wt., respectively. PCB and TEQ concentrations were close to the threshold values that can, under laboratory conditions, elicit toxic effects in ranchmink. Therefore, any additional exposures of these populations toTEQs might adversely affect their populations.  相似文献   
7.
Dredging is a very important procedure for harbor management. InItaly the guidelines for the offshore dumping of dredged materials are issued by the Ministry of Environment. Theydescribed a few steps of dredging activities, such as thesampling strategy, but do not deal with limits or guide-valuesfor the chemical, physical and biological composition of theresulting sediments. The quality of dredged materials is mainlydependent on the presence of inorganic and organic pollutants.In particular, polychlorinated biphenyls (PCBs) and organo-chlorinated pesticides are seen as a high priority inmarine environment by international organizations because oftheir persistence, toxicity and bioaccumulation capacity.In this article the presence of some PCBs and organo-chlorinatedpesticides in sediment samples collected from the harbor ofLivorno (Northern Tyrrhenian Sea) was investigated. Theconcentration of HCHs, Aldrin, Chlordanes, DDEs, DDTs, and PCBsin 12 representative sites ranged between <1 g kg–1and 95, 19, 32, 35, 107, and 111 g kg–1, respectively.The application of univariate and multivariate statisticaltechniques, such as linear regression analysis and principalcomponent analysis, to the experimental data showed a differentdistribution of PCBs in the two sediment layers. On thecontrary, the vertical distribution of the other investigatedpollutants was more homogeneous and affected by randomvariability. The multivariate approach was an important tool to establish more rational criteria for the management of dredged materials.  相似文献   
8.
A total of 198 agricultural soil samples were collected from Zhangjiagang and Changshu in Southern Jiangsu for analysis of 13 polychlorinated biphenyls (PCBs) in order to assess the levels of pollution, sources, area distribution, and potential risk for the environment. All methods were rigorously tested and an adequate quality control was ensured. Only one site had no PCBs residues, and the highest total PCBs concentration in the surface soils was 32.83 ng/g. The average concentration in all the soil samples was 4.13 ng/g, signaling low-level pollution. Tetra-, penta-, and hexa-chlorinated biphenyls were dominant species in soil samples, accounting for more than 75% ofΣPCBs in the soil samples. PCB118 was the most abundant congener in all the samples. The PCB118 was about 20% ofΣPCBs. The soil organic matter content showed only a weak correlation with the levels of all PCB congeners, in which a better correlation was noted for the more volatile lighter PCB congeners than for the heavier homologues. To a certain extent, the sources and land use seemed to influence the levels of PCBs.  相似文献   
9.
SBR法处理中药材有机废水工艺研究   总被引:2,自引:0,他引:2  
应用SBR法对中药材有机废水进行了研究。考察了CODCR、BOD5、SS、NH3-H的处理效果,以及PH、水温、污泥负荷等条件对去除率的影响。运行结果表明,PHO 6.0-9.0、t为15-30℃、污沁荷0.3kgBOD5/kgMLSS.d,运行程序:进水0.5h(限制曝气)、曝气10h、脱氮1.5h,沉降0.5h,排水0.5h、闲置11h,周期时间24h时CODCR去除率88%、BOD594%、  相似文献   
10.
WTO:中国环境立法挑战与整合   总被引:3,自引:0,他引:3  
探讨了我国“入世”后环境立法所面对的挑战问题。分析了世贸组织法中的环保条款及中国环境立法不完善之处,指出这将对中国“入世”后对外贸易产生不利影响。对完善中国环境立法提出建议。  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