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   7064篇
  免费   1363篇
  国内免费   159篇
安全科学   310篇
废物处理   69篇
环保管理   1917篇
综合类   3485篇
基础理论   731篇
污染及防治   429篇
评价与监测   1339篇
社会与环境   251篇
灾害及防治   55篇
  2025年   60篇
  2024年   194篇
  2023年   208篇
  2022年   219篇
  2021年   223篇
  2020年   234篇
  2019年   198篇
  2018年   165篇
  2017年   258篇
  2016年   297篇
  2015年   297篇
  2014年   340篇
  2013年   411篇
  2012年   447篇
  2011年   465篇
  2010年   319篇
  2009年   344篇
  2008年   287篇
  2007年   431篇
  2006年   396篇
  2005年   305篇
  2004年   265篇
  2003年   270篇
  2002年   257篇
  2001年   200篇
  2000年   198篇
  1999年   158篇
  1998年   121篇
  1997年   118篇
  1996年   121篇
  1995年   93篇
  1994年   86篇
  1993年   60篇
  1992年   49篇
  1991年   56篇
  1990年   26篇
  1989年   30篇
  1988年   36篇
  1987年   30篇
  1986年   24篇
  1985年   19篇
  1984年   22篇
  1983年   22篇
  1982年   27篇
  1981年   27篇
  1980年   31篇
  1979年   28篇
  1978年   18篇
  1975年   15篇
  1973年   18篇
排序方式: 共有8586条查询结果,搜索用时 15 毫秒
661.
    
Research has continued to indicate that the proliferation of information and communication technologies (ICTs) has the potential to alleviate poverty in developing countries. While theoretically, there are several mechanisms through which ICT may reduce poverty, they have not been empirically tested sufficiently. The present study aimed to recognize the mechanisms through which ICT may reduce poverty for a sample of 37 economies in the Sub-Saharan Africa (SSA) region during the period 2003–2019. Altering the income distribution, improving the ecological system, increasing the employment rate, increasing per capita income, and improving institutional quality were the assumed mechanisms through which ICT may reduce poverty. The results of the two-step system GMM technique showed that while an increase in the per capita income and employment rate contributed positively to poverty reduction, improvement in the environmental quality increased the poverty rate. The causal mediation analysis findings showed that ICT strengthened the negative impact of worsening the quality of the environment on poverty. However, the strengthened positive impact of ICT on poverty through employment and per capita income was greater than the negative influence through the environmental mechanism. Thus, all national strategies or initiatives aimed at reducing poverty in SSA must incorporate pro-poor ICT policies.  相似文献   
662.
酸化-吹气-吸收法测定水及废水中的硫化物   总被引:1,自引:0,他引:1       下载免费PDF全文
文志明  林大泉 《环境化学》1994,13(2):170-175
本文设计了流化物测定的酸化-吹气-吸收装置,验证了装置对硫化物的回收效果,对硫化物标准溶液的配制及其稳定性进行了研究,对分析条件进行了最佳选择,建立了亚甲基蓝光度法测定硫化物的分析方法,并对实际作品进行了测定.本方法的检出限为0.005mgS2-/1,线性范围为0.005—0.700mg S2-/l,可应用于水和废水样品中微量硫化物的测定.  相似文献   
663.
Recent models of choosiness in mate choice have identified two particularly important factors: the potential reproductive rate (PRR) of the choosing sex relative to that of the chosen sex, and the variation in quality of potential mates. This experimental study tested how these factors affected choosiness in male and female sand gobies, Pomatoschistus minutus. We manipulated relative PRR by means of water temperature, and mate quality by means of body length. The choosing male or female was offered a choice between two mates with either a small or a large difference in body length representing a small or a large variation in mate quality. Choosiness was measured as (1) preference for the larger mate, and (2) as whether or not spawning occurred with the smaller mate, while the larger mate was visible but screened off. We found that females preferred large males, and that their level of choosiness was affected by variation in male quality, but not by their own relative PRR. Males, on the other hand, seemed unselective in all treatments and were in general more likely than females to spawn with their provided partner. This suggests that in the sand goby, variation in male mate quality has a greater influence than relative PRR on facultative changes in female choosiness. However, a general difference in PRR between males and females may be one important factor explaining the observed sex difference in choosiness. Received: 17 April 2000 / Revised: 24 June 2000 / Accepted: 17 July 2000  相似文献   
664.
太湖流域3种氯酚类化合物水质基准的探讨   总被引:13,自引:7,他引:13  
按照美国地面水水质基准制定的程序和规范,筛选了太湖流域广泛存在的水生生物物种并收集了相应的基础毒性数据,探讨了五氯酚(PCP)、2,4-二氯酚(2,4-DCP)和2,4,6-三氯酚(2,4,6-TCP)在我国太湖地区的水生态基准的定值.同时采用蒙特卡罗构建物种敏感度分布(SSD)曲线和生态毒理模型方法预测了3种氯酚类化合物对太湖水生生物的急性基准浓度(CMC)和慢性基准浓度(CCC).结果表明,基于EPA规范方法和急慢性毒性比率得到的PCP、2,4-DCP和2,4,6-TCP3种氯酚类化合物的CMC值分别为25、908和594μg·L-1,CCC值分别为12、176和162μg·L-1;基于SSD曲线得到的CMC值分别为25、818和648μg·L-1,CCC值分别为6、75和198μg·L-1;基于生态毒理模型得到的CCC值分别为4、15和67μg·L-1,显示出3种方法得到的氯酚类化合物的CMC或CCC在同一个数量级上,但在数值上由生态毒理模型得出的CCC要小于其它两种方法,并且除PCP的急慢性基准值与美国EPA推出的水生态基准值相近外,其它两种氯酚类化合物的急慢性基准值均低于美国EPA推出的急慢性基准值.研究结果希望能为我国水质基准的制定提供一些有用的线索.  相似文献   
665.
本文简要分析了环境质量评价中目前广泛应用的各种评价方法与模型。在此基础上提出环境质量综合评判-灰色关联优势分析复合模型,应用于黄山风景区景观生态环境质量的综合评价,取得了满意的结果。  相似文献   
666.
    
Addition of plant residue into soils improves soil physiochemical properties and its fertility. Rapeseed residue is an emerging N source to paddy soils via rice-rape double-cropping practice. The objective of this study was to evaluate the effects of rapeseed residue and eggshell waste on chemical changes and enzyme activity in the rice paddy soil. The powdered eggshells at 0, 1, 3, and 5% were applied once to 7.0 kg paddy repacked soils in each pot treated with the rapeseed residue or the conventional N, P, and K fertilisers. Eight rice seedlings (Oriza sativa L. cv. Ilmibyeo) (40 days after sowing) were transplanted to the treated each pot. The contents of total C (TC) and N (TN), and organic matter (OM) were significantly increased in soils treated with the rapeseed residue compared to the N, P, and K fertilisers. With the addition of eggshell containing ~92% CaCO3, a considerable increase of soil pH was observed in soils treated with the rapeseed residue and the N, P, and K fertilisers, compared to the untreated soil. Activities of β-glucosidase, urease, and arylsulfatase enzymes were higher in soils treated with the rapeseed residue than soils treated with the N, P, and K fertilisers. The eggshell additions at 1, 3, and 5% into soils treated with the rapeseed residue increased enzyme activity mainly resulting from N mineralisation, whereas no change in enzyme activity was observed in the soils treated with the NPK fertiliser. The combined use of the rapeseed residue and the eggshells can be beneficial to improve soil environment.  相似文献   
667.
Although fish are usually thought of as victims of water quality degradation, it has been proposed that some planktivorous species may improve water quality through consumption of algae and sequestering of nutrients via growth. Within most numerical water quality models, the highest trophic level modeled explicitly is zooplankton, prohibiting an investigation of the effect a fish species may be having on its environment. Conversely, numerical models of fish consumption do not typically include feedback mechanisms to capture the effects of fish on primary production and nutrient recycling. In the present study, a fish bioenergetics model is incorporated into CE-QUAL-ICM, a spatially explicit eutrophication model. In addition to fish consumption of algae, zooplankton, and detritus, fish biomass accumulation and nutrient recycling to the water column are explicitly accounted for. These developments advance prior modeling efforts of the impact of fish on water quality, many of which are based on integrated estimates over an entire system and which omit the feedback the fish have through nutrient recycling and excretion. To validate the developments, a pilot application was undertaken for Atlantic menhaden (Brevoortia tyrannus) in Chesapeake Bay. The model indicates menhaden may reduce the algal biomass while simultaneously increasing primary productivity.  相似文献   
668.
大气臭氧污染的生物学指标监测评价   总被引:1,自引:0,他引:1  
臭氧是具有很大危害性的大气污染物之一,近150年来大气对流层中的臭氧质量浓度已经增加了36%,在今后50~100年内还将以每年0.5%-2%的速度继续升高。植物对大气污染物的敏感性是由多种因素相互作用而成的复杂综合性状。以不同质量浓度(分别为0.0、1.0、2.0、3.0、4.0、5.0 mg·L-1)臭氧(O3)胁迫下的不同类型植物为例,观察植物在不同时间(2、4、6、8 h)的外观伤害症状和细胞膜透性与O3质量浓度的相关性。试验结果表明:不同植物对O3的敏感度不同,蔬菜对臭氧相对较敏感;低质量浓度长时间和高质量浓度短时间的作用条件下,植物的受害症状基本相同,典型症状表现为叶片上散布细密点状斑,斑点的颜色呈白色、黄色、棕褐色,也有褪绿斑;植物细胞膜透性数据即电导率直接反映植物受损程度。综合植物外观症状指标与生理生化指标建立了相对定量化的大气质量生物学指标评价模式,即划分为轻微(0-0.2)、轻度(0.2-0.4)、中度(0.4-0.6)、高度(0.6-0.8)、严重(0.8-1.0)5个受害等级,以定量的判断O3气体对植物的伤害。  相似文献   
669.
非常规多水源双膜工艺处理后浓缩水的水质特性   总被引:1,自引:0,他引:1  
利用常规和非常规多水源经RO处理后作为新水源,与非常规单一城市污水厂水源比较,多水源双膜处理工艺产生的浓水水质有所不同。浓水水质检测主要指标包括无机盐(Cl-、SO42-、TDS、全盐量)、有机物(BOD、COD)、氮营养物(NH4+-N、TN)、碱度、硬度等。通过实际工程运行水质动态监测,初步探讨了RO浓水的水质规律及其影响因素,为RO浓水处理处置技术深入研究奠定了基础。  相似文献   
670.
Free-ranging adult male baboons give loud two-syllable wahoo calls during dawn choruses, interactions between groups, when chasing females, and in aggressive interactions with other males. Previous research has shown that the rate and duration of these contest wahoos are correlated with a males competitive ability: high-ranking males call more often, call at faster rates, and call for longer bouts than do low-ranking males. Here we report that acoustic features of wahoos also reveal information about male competitive ability. High-ranking males give wahoos with higher fundamental frequencies (F0) and longer hoo syllables. Within-subject analyses revealed that, as males fall in rank, the hoo syllables tend to shorten within a period of months. As males age and continue to fall in rank, F0 declines, hoo syllables shorten, and formant dispersion decreases. Independent of age and rank, within bouts of calling F0 declines and hoo syllables become shorter. Because wahoos are often given while males are running or leaping through trees, variation in these acoustic features may function as an indicator of a males stamina. The acoustic features of contest wahoos thus potentially allow listeners to assess a males competitive ability.Communicated by C. Nunn  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