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   30863篇
  免费   408篇
  国内免费   500篇
安全科学   999篇
废物处理   1245篇
环保管理   4452篇
综合类   5085篇
基础理论   8198篇
环境理论   11篇
污染及防治   8037篇
评价与监测   1825篇
社会与环境   1703篇
灾害及防治   216篇
  2022年   265篇
  2021年   277篇
  2020年   274篇
  2019年   270篇
  2018年   462篇
  2017年   453篇
  2016年   696篇
  2015年   526篇
  2014年   727篇
  2013年   2464篇
  2012年   961篇
  2011年   1400篇
  2010年   1103篇
  2009年   1163篇
  2008年   1373篇
  2007年   1445篇
  2006年   1255篇
  2005年   1004篇
  2004年   1071篇
  2003年   990篇
  2002年   933篇
  2001年   1212篇
  2000年   880篇
  1999年   550篇
  1998年   410篇
  1997年   399篇
  1996年   407篇
  1995年   471篇
  1994年   445篇
  1993年   386篇
  1992年   379篇
  1991年   371篇
  1990年   387篇
  1989年   382篇
  1988年   311篇
  1987年   279篇
  1986年   276篇
  1985年   281篇
  1984年   350篇
  1983年   307篇
  1982年   322篇
  1981年   301篇
  1980年   244篇
  1979年   273篇
  1978年   212篇
  1977年   197篇
  1975年   183篇
  1974年   191篇
  1973年   183篇
  1972年   204篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
211.
本研究在运用三维荧光光谱示踪平水期东平湖DOM荧光特征的基础上,进一步分析其与氢氧同位素指标的相关性,并在此基础上尝试对大气降水的DOC贡献进行估算,以期为东平湖的污染控制及治理提供依据.结果表明,东平湖平水期DOM主要由类蛋白组分(C1和C4)和类腐殖质组分(C2和C3)构成,以类酪氨酸组分C1为主,C1所占比重将近50%.平水期东平湖DOM同时受陆源、内源及大气降水的影响,但以内源输入为主;外源输入中大气降水补给与大汶河输入所占比例相当;大气降水中的溶解性有机碳输入可能会对东平湖DOM产生不可忽视的影响,需进一步系统研究.氢氧稳定同位素与溶解态有机碳以及类腐殖质荧光之间呈显著相关关系,可以在一定程度上指示DOM的变化趋势.  相似文献   
212.
Scholars continue to search for solutions to shift climate change skeptics’ views on climate science and policy. However, research has shown that certain audiences are resistant to change regarding environmental issues. To explore this issue further, we examine the presence of reactance among different audiences in response to simple, yet prominently used, climate change messages. Our results show that emphasizing the scientific consensus of climate change produces reactance, but only among people who question the existence of climate change. Moreover, adding political identification to the model as an additional moderating variable shows the increases in reactance occur among Republicans who question the existence of climate change. Finally, our results show that reactance to climate change messaging may lead to backfiring effects on important outcomes tied to climate change such as risk perceptions, climate change beliefs, and support for mitigation policies.  相似文献   
213.
Production facilities serve to transform raw materials into products, usually with the goal of achieving a designated output, in terms of quantity and quality, with the minimum of cost and labour. With the aid of production planning and controlling (PPC) systems, raw material inputs, and labour can be planned to achieve a determined output of products. In general, the role of environmental and social aspects is neglected in production planning processes. Because of the growing pressure from politics and customers, sustainable production of products is becoming more important. One possibility for supporting sustainable manufacturing is, to integrate sustainable aspects in the production planning process. This paper presents input and output information for current PPC systems and discusses the need for additional information necessary for sustainable PPC. For this approach, a text review of cooperate social responsibility (CSR) reporting indicators provided by the GRI was performed. Based on the text review, an input-output model has been developed for conventional and another one for sustainable PPC systems. Through the comparison of the two input-output models, challenges and requirements for sustainable PPC systems have been defined as a basis for future work and analyses.  相似文献   
214.

Tendencies in the dynamics of harvested northern fur seal (Callorhinus ursinus) population on the Tyulenii Island have been analyzed in detail. The results show that retardation of reproduction (decrease in the numbers of pups) and decline in the survival of young females (up to 3 years of age) by the late 1980s resulted in a reduction of the total number of females and a significant increase in the proportion of older females. This tendency changed during the later observation period (after 1988–1989) due to increase in the survival of young females: the female population has gradually recovered, with the proportion of young females increasing at the expense of old females (aged over 10 years). The age composition of males has also changed: the proportion of young animals has decreased, while that of large mature males (bulls) has increased. Moreover, the number of bulls continues to increase and has already exceeded the level that formerly provided for the well-being of the population. This, a paradoxical situation has arisen: the numbers of females and bulls are increasing, whereas pup production remains at a low level.

  相似文献   
215.
Yang  W.  Deng  D. G.  Meng  X. L.  Zhang  S. 《Russian Journal of Ecology》2019,50(4):352-360
Russian Journal of Ecology - Temporal and spatial variations of phytoplankton community in Lake Erhai were investigated from May 2010 to April 2011. A total of 124 species belonging to 8 phyla and...  相似文献   
216.
醌介导染料脱色菌株的分离鉴定及特性   总被引:1,自引:0,他引:1       下载免费PDF全文
实验分离获得1株能够利用醌化合物使磺酸化偶氮染料脱色的菌株JL,通过形态特征、16S rDNA与16S-23S区间序列分析表明,该菌株为蜡状芽孢杆菌(命名为Bacillus cereus JL).菌株JL使酸性大红3R脱色的最佳条件为葡萄糖浓度1g/L, pH值为5~7,温度30℃,接种量0.25g/L.蒽醌-2-磺酸(AQS)、蒽醌-2,6-二磺酸(AQDS)和2-羟基-1,4-萘醌(Lawsone)均能显著提高酸性大红3R的脱色速率,其中AQS的促进作用最为明显.研究发现, 0.1mmol/L AQS能够使菌株JL对2.0mmol/L酸性大红3R保持较高的脱色速率,而且能使多种偶氮染料脱色,表现出较好的底物广谱性.利用高效液相色谱-质谱鉴定了AQS介导的酸性大红3R脱色产物,表明酸性大红3R的偶氮键发生断裂, AQS在这一过程中仅起到电子传递的作用.  相似文献   
217.
218.
Reef‐fish management and conservation is hindered by a lack of information on fish populations prior to large‐scale contemporary human impacts. As a result, relatively pristine sites are often used as conservation baselines for populations near sites affected by humans. This space‐for‐time approach can only be validated by sampling assemblages through time. We used archaeological remains to evaluate whether the remote, uninhabited Northwestern Hawaiian Islands (NWHI) might provide a reasonable proxy for a lightly exploited baseline in the Main Hawaiian Islands (MHI). We used molecular and morphological techniques to describe the taxonomic and size composition of the scarine parrotfish catches present in 2 archaeological assemblages from the MHI, compared metrics of these catches with modern estimates of reproductive parameters to evaluate whether catches represented by the archaeological material were consistent with sustainable fishing, and evaluated overlap between size structures represented by the archaeological material and modern survey data from the MHI and the NWHI to assess whether a space‐for‐time substitution is reasonable. The parrotfish catches represented by archaeological remains were consistent with sustainable fishing because they were dominated by large, mature individuals whose average size remained stable from prehistoric (AD approximately 1400–1700) through historic (AD 1700–1960) periods. The ancient catches were unlike populations in the MHI today. Overlap between the size structure of ancient MHI catches and modern survey data from the NWHI or the MHI was an order of magnitude greater for the NWHI comparison, a result that supports the validity of using the NWHI parrotfish data as a proxy for the MHI before accelerated, heavy human impacts in modern times. Evidencia Arqueológica de la Validez de Poblaciones de Peces en Arrecifes Sin Explotar como Objetivos de Apoderamiento para Poblaciones Actuales  相似文献   
219.
Conservation decision makers commonly use project‐scoring metrics that are inconsistent with theory on optimal ranking of projects. As a result, there may often be a loss of environmental benefits. We estimated the magnitudes of these losses for various metrics that deviate from theory in ways that are common in practice. These metrics included cases where relevant variables were omitted from the benefits metric, project costs were omitted, and benefits were calculated using a faulty functional form. We estimated distributions of parameters from 129 environmental projects from Australia, New Zealand, and Italy for which detailed analyses had been completed previously. The cost of using poor prioritization metrics (in terms of lost environmental values) was often high—up to 80% in the scenarios we examined. The cost in percentage terms was greater when the budget was smaller. The most costly errors were omitting information about environmental values (up to 31% loss of environmental values), omitting project costs (up to 35% loss), omitting the effectiveness of management actions (up to 9% loss), and using a weighted‐additive decision metric for variables that should be multiplied (up to 23% loss). The latter 3 are errors that occur commonly in real‐world decision metrics, in combination often reducing potential benefits from conservation investments by 30–50%. Uncertainty about parameter values also reduced the benefits from investments in conservation projects but often not by as much as faulty prioritization metrics.  相似文献   
220.
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