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   768篇
  免费   164篇
  国内免费   155篇
安全科学   28篇
废物处理   7篇
环保管理   87篇
综合类   570篇
基础理论   283篇
环境理论   2篇
污染及防治   26篇
评价与监测   32篇
社会与环境   43篇
灾害及防治   9篇
  2024年   6篇
  2023年   32篇
  2022年   29篇
  2021年   38篇
  2020年   32篇
  2019年   53篇
  2018年   24篇
  2017年   45篇
  2016年   38篇
  2015年   41篇
  2014年   37篇
  2013年   72篇
  2012年   80篇
  2011年   57篇
  2010年   46篇
  2009年   47篇
  2008年   38篇
  2007年   42篇
  2006年   45篇
  2005年   37篇
  2004年   30篇
  2003年   22篇
  2002年   22篇
  2001年   29篇
  2000年   21篇
  1999年   14篇
  1998年   35篇
  1997年   23篇
  1996年   12篇
  1995年   11篇
  1994年   7篇
  1993年   6篇
  1992年   9篇
  1991年   2篇
  1990年   3篇
  1988年   2篇
排序方式: 共有1087条查询结果,搜索用时 17 毫秒
1.
Marine coastal ecosystems, commonly referred to as blue ecosystems, provide valuable services to society but are under increasing threat worldwide due to a variety of drivers, including eutrophication, development, land-use change, land reclamation, and climate change. Ecological restoration is sometimes necessary to facilitate recovery in coastal ecosystems. Blue restoration (i.e., in marine coastal systems) is a developing field, and projects to date have been small scale and expensive, leading to the perception that restoration may not be economically viable. We conducted a global cost–benefit analysis to determine the net benefits of restoring coral reef, mangrove, saltmarsh, and seagrass ecosystems, where the benefit is defined as the monetary value of ecosystem services. We estimated costs from published restoration case studies and used an adjusted-value-transfer method to assign benefit values to these case studies. Benefit values were estimated as the monetary value provided by ecosystem services of the restored habitats. Benefits outweighed costs (i.e., there were positive net benefits) for restoration of all blue ecosystems. Mean benefit:cost ratios for ecosystem restoration were eight to 10 times higher than prior studies of coral reef and seagrass restoration, most likely due to the more recent lower cost estimates we used. Among ecosystems, saltmarsh had the greatest net benefits followed by mangrove; coral reef and seagrass ecosystems had lower net benefits. In general, restoration in nations with middle incomes had higher (eight times higher in coral reefs and 40 times higher in mangroves) net benefits than those with high incomes. Within an ecosystem type, net benefit varied with restoration technique (coral reef and saltmarsh), ecosystem service produced (mangrove and saltmarsh), and project duration (seagrass). These results challenge the perceptions of the low economic viability of blue restoration and should encourage further targeted investment in this field.  相似文献   
2.
Aerobic treatment of swine manure was coupled with anaerobic digestion and microalgal cultivation. A 14-day aerobic treatment reduced the total solid content of swine manure by >15%. Ammonia and carbon dioxide were stripped by the air supplied, and this off-gas was further used to aerate the culture of Chlorella vulgaris. The microalgal growth rates in Bristol medium and the wastewater with the off-gas increased from 0.08 to 0.22 g/L/d and from 0.15 to 0.24 g/L/d, respectively. Meanwhile, the aerobically treated swine manure showed a higher methane yield during anaerobic digestion. The experimental results were used to establish a demonstration unit consisting of a 100 L composter, a 200 L anaerobic digester, a 60 L tubular photobioreactor, and a 300 L micro-open raceway pond.  相似文献   
3.
The availability of genomic data for an increasing number of species makes it possible to incorporate evolutionary processes into conservation plans. Recent studies show how genetic data can inform spatial conservation prioritization (SCP), but they focus on metrics of diversity and distinctness derived primarily from neutral genetic data sets. Identifying adaptive genetic markers can provide important information regarding the capacity for populations to adapt to environmental change. Yet, the effect of including metrics based on adaptive genomic data into SCP in comparison to more widely used neutral genetic metrics has not been explored. We used existing genomic data on a commercially exploited species, the giant California sea cucumber (Parastichopus californicus), to perform SCP for the coastal region of British Columbia (BC), Canada. Using a RAD-seq data set for 717 P. californicus individuals across 24 sampling locations, we identified putatively adaptive (i.e., candidate) single nucleotide polymorphisms (SNPs) based on genotype–environment associations with seafloor temperature. We calculated various metrics for both neutral and candidate SNPs and compared SCP outcomes with independent metrics and combinations of metrics. Priority areas varied depending on whether neutral or candidate SNPs were used and on the specific metric used. For example, targeting sites with a high frequency of warm-temperature-associated alleles to support persistence under future warming prioritized areas in the southern coastal region. In contrast, targeting sites with high expected heterozygosity at candidate loci to support persistence under future environmental uncertainty prioritized areas in the north. When combining metrics, all scenarios generated intermediate solutions, protecting sites that span latitudinal and thermal gradients. Our results demonstrate that distinguishing between neutral and adaptive markers can affect conservation solutions and emphasize the importance of defining objectives when choosing among various genomic metrics for SCP.  相似文献   
4.
The loss of yields from agricultural production due to the presence of pests has been treated over the years with synthetic pesticides, but the use of these substances negatively affects the environment and presents health risks for consumers and animals. The development of agroecological systems using biopesticides represents a safe alternative that contributes to the reduction of agrochemical use and sustainable agriculture. Microalgae are able to biosynthesize a number of metabolites with potential biopesticidal action and can be considered potential biological agents for the control of harmful organisms to soils and plants. The present work aims to provide a critical perspective on the consequences of using synthetic pesticides, offering as an alternative the biopesticides obtained from microalgal biomass, which can be used together with the implementation of environmentally friendly agricultural systems.  相似文献   
5.
Strategies to reduce, halt, and reverse global declines in marine biodiversity are needed urgently. We reviewed, coded, and synthesized historical and contemporary marine conservation strategies of the Kitasoo/Xai'xais First Nation in British Columbia, Canada to show how their approaches work. We assessed whether the conservation actions classification system by the Conservation Measures Partnership was able to encompass this nation's conservation approaches. All first-order conservation actions aligned with the Kitasoo/Xai'xais First Nation's historical and contemporary marine conservation actions; hereditary chief management responsibility played a key role. A conservation ethic permeates Kitasoo/Xai'xais culture, and indigenous resource management and conservation existed historically and remains strong despite extreme efforts by colonizers to suppress all indigenous practices. The Kitasoo/Xai'xais's embodiment of conservation actions as part of their worldview, rather than as requiring actions separate from everyday life (the norm in nonindigenous cultures), was missing from the conservation action classification system. The Kitasoo/Xai'xais are one of many indigenous peoples working to revitalize their governance and management authorities. With the Canadian government's declared willingness to work toward reconciliation, there is an opportunity to enable First Nations to lead on marine and other conservation efforts. Global conservation efforts would also benefit from enhanced support for indigenous conservation approaches, including expanding the conservation actions classification to encompass a new category of conservation or sacredness ethic.  相似文献   
6.
南黄海东部海域浮游生态系统要素季节变化的模拟研究   总被引:5,自引:0,他引:5  
利用海洋生态系统动力学垂直一维物理-生物耦合模式模拟研究了南黄海东部海域浮游生态系统要素垂直分布的季节变化.物理亚模型为一维POM模式(Princeton Ocean Model),基于文献结果对垂直混合系数Kh和Km进行了调整;生态亚模型为ERSEM模式(European Regional Sea Ecosystem Model),主要考虑浮游植物、浮游动物、细菌、底栖碎屑和营养盐(氮、磷、硅)等状态变量.模拟结果表明,浮游植物出现一年双峰的态势和夏季次表层叶绿素最大值的现象,春、秋季水华期间,表层叶绿素峰值分别为3.25 mg/m3和0.71 mg/m3.浮游动物和细菌在春季水华后表层出现峰值,分别为143.6 mg C/m3和23.55 mg C/m3.硝酸盐、磷酸盐和硅酸盐的垂直分布均在5-11月呈现表层浓度低、底层浓度高的分布.通过计算碳通量可以看出,在春、夏季,浮游植物对无机碳的摄取量分别为58.944 g C·m-2·quarter-1和68.276 g C·m-2·quarter-1,高于细菌对非生命有机碳的摄取.在冬季,细菌对非生命有机碳的摄取超过浮游植物对无机碳的摄取量.浮游动物在冬季主要摄食细菌,占71%;春、夏季主要摄食浮游植物,可达67.5%.浮游植物对碳的释放主要是以DOC的形式,约占90%.  相似文献   
7.
碳酸钙中的碳能否被微藻利用这一问题一直处于争论中。本文在开放与隔离空气CO2环境下用含有碳酸钙粉末和不同浓度乙酰唑胺的培养液培养衣藻和小球藻。通过双向同位素示踪技术,定量描述出不同条件下微藻对碳酸钙碳源的利用份额。在隔离空气CO2的环境下,微藻对碳酸钙碳源的利用份额明显大于开放环境下。在开放环境下,随着培养液中乙酰唑胺浓度增加,生物量减少,微藻对固有无机碳源的利用份额减少,对碳酸钙碳源的利用份额增加。在隔离空气CO2的环境下,随着培养液中乙酰唑胺浓度增加,微藻生物量增加,衣藻对固有无机碳源的利用份额增加,对碳酸钙碳源的利用份额减少,而小球藻反之。微藻主要是通过利用碳酸钙溶蚀的可溶性无机碳(DIC)这种间接方式来利用碳酸钙碳源。而外界大气CO2浓度和胞外碳酸酐酶是影响碳酸钙溶解的重要因素,因此其也明显的影响着微藻对碳酸钙碳源的利用。  相似文献   
8.
本文以红枫湖、百花湖和阿哈水库中的微藻为研究对象,通过测定湖水中的DIC含量,微藻胞外碳酸酐酶活力和藻体的稳定碳同位素组成等信息,来研究湖泊微藻的碳同位素组成对全球气候变化的响应。结果发现:水体无机碳和微藻胞外碳酸酐酶活力是影响湖泊微藻稳定碳同位素组成变化的决定性因素。本研究所获得的认识将在全球气候变化方面具有重要意义。  相似文献   
9.
广东省船舶排放源清单及时空分布特征研究   总被引:12,自引:3,他引:9  
分别采用基于船舶引擎功率和耗油量的排放因子法,估算了广东省地区2010年的船舶排放清单,并选取客货运输吞吐量、航道通航能力因子和港口地理坐标等数据作为权重因子,研究了该地区各类船舶排放的时空分布特征.结果表明,广东省各类船舶在2010年的SO2、NO x、CO、PM10、PM2.5和VOCs排放总量分别为14.6×104t、23.1×104t、3.0×104t、7.9×103t、7.2×103t和9.3×103t.广东省客货运输船舶月排放波动较小;渔业船舶在1月、4月和11月份的排放比例最高.广东省客货运输船舶水域排放集中在西江干线水道和珠江三角洲高等级航道网内,港口排放主要分布在广东省珠江三角洲沿海发达城市地区;渔船港口排放量呈显著的沿海条带状空间分布特征.  相似文献   
10.
随着超高压联网工程建设项目不断增多,取得巨大经济效益的同时,其电缆安全性日益受到关注。采用标准实验方法,研究电缆绝缘油对8种占据不同生态位的海洋生物(费氏弧菌(Vibrio fischeri)、牟氏角毛藻(Chaetoceros mueleri)、卤虫(Artemia sp.)、蒙古裸腹溞(Moina mongolica)、凡纳滨对虾(Litopenaeus vannamei)、裸项栉鰕虎鱼(Ctenogobius gymnauchen)、双齿围沙蚕(Perinereis aibuhitensis)、菲律宾蛤仔(Ruditapes philippinarum))的急性毒性,同时进行了电缆绝缘油对裸项栉鰕虎鱼14 d延长毒性实验和电缆绝缘油对蒙古裸腹溞的慢性毒性。结果表明,电缆绝缘油在50%饱和溶解浓度下未对费氏弧菌产生明显的发光抑制作用;对牟氏角毛藻、凡纳滨对虾、裸项栉鰕虎鱼、双齿围沙蚕和菲律宾蛤仔等5种生物未表现出急性毒性影响,其LC50均大于饱和浓度;对卤虫的96 h-LC50为17.07%,LOEC为12.5%,NOEC为6.25%;对蒙古裸腹溞96 h-LC50为29.75%,LOEC为25.0%,NOEC为12.5%;电缆绝缘油对卤虫和蒙古裸腹溞有剧毒。对裸项栉鰕虎鱼成鱼14 d延长毒性LC50大于500 000 mg·L~(-1);对蒙古裸腹溞母溞存活数的NOEC为625μg·L~(-1),LOEC为1 250μg·L~(-1);对母溞存活期的NOEC为312μg·L~(-1),LOEC为625μg·L~(-1);对产胎数的NOEC为625μg·L~(-1),LOEC为1 250μg·L~(-1);对产幼溞数的NOEC为625μg·L~(-1),LOEC为1 250μg·L~(-1)。  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