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   15525篇
  免费   132篇
  国内免费   94篇
安全科学   401篇
废物处理   571篇
环保管理   1800篇
综合类   3413篇
基础理论   3902篇
环境理论   14篇
污染及防治   3887篇
评价与监测   901篇
社会与环境   771篇
灾害及防治   91篇
  2022年   125篇
  2021年   114篇
  2020年   99篇
  2019年   128篇
  2018年   232篇
  2017年   224篇
  2016年   307篇
  2015年   276篇
  2014年   370篇
  2013年   1053篇
  2012年   446篇
  2011年   660篇
  2010年   521篇
  2009年   582篇
  2008年   705篇
  2007年   670篇
  2006年   590篇
  2005年   523篇
  2004年   447篇
  2003年   455篇
  2002年   470篇
  2001年   533篇
  2000年   402篇
  1999年   250篇
  1998年   167篇
  1997年   190篇
  1996年   204篇
  1995年   227篇
  1994年   235篇
  1993年   184篇
  1992年   171篇
  1991年   197篇
  1990年   194篇
  1989年   184篇
  1988年   137篇
  1987年   132篇
  1986年   142篇
  1985年   113篇
  1984年   126篇
  1983年   128篇
  1982年   136篇
  1981年   133篇
  1980年   112篇
  1979年   128篇
  1978年   95篇
  1977年   102篇
  1976年   88篇
  1975年   94篇
  1973年   96篇
  1967年   91篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
This work was undertaken to analyze nutrient contents of vegetation in an alpine meadow—Tungnath, North-West Himalaya, India. The study pertains to the uptake, transfer and release of four main macronutrients (organic carbon, total nitrogen, total potassium and total phosphorus) in grazed (exposed to extensive grazing by cattles) and ungrazed (grazing completely prohibited) communities. Mineral concentration was recorded higher for the ungrazed sites compared to the grazed sites, and maximum standing state of nutrients was found in roots. Belowground compartment (roots) contributed maximum share of mineral elements to soil. Litter nutrients release was low because of low microbial activity and continuous removal of phytomass. Observations reveal that there was very little amount of nutrient release from phytomass and vegetation in alpine are very poor source of mineral recycling. Low transfer rate of minerals from one compartment to other is adequate for greater amount of these minerals that are translocated back into the storage organs. A small proportion get removed through rain splash or through the removal of hay during grazing as relatively high release rates in ungrazed sites when compared to grazed sites was observed. This translocation can be considered as an important adaptation in alpine plants for survival during adverse environmental conditions, against all types of biotic pressures and also for regeneration in the forthcoming growing season.  相似文献   
972.
A laboratory-scale bioremediation unit was designed, built and tested for the bio-removal of several Direct textile dyes. Four experiments were carried out to assess the efficiency of the bioremediation unit using Aspergillus niger fungal strain. Three commonly used Direct dyes and textile dyes mixture (simulated effluent: Direct brown, Direct violet, Direct green) were tested in this study. The strain of A. niger was efficient in the removal of the three Direct dyes. The decolorization percentages of the dyes after 24 h of incubation were 56.2, 51.7, and 95.4% for Direct brown, Direct green, Direct violet dyes, respectively. The percentages increased up to 79.4, 86.4, and 96.7% after 72 h of incubation for the same dyes, respectively. The results also showed that the fungal strain reduced the chemical oxygen demand values of simulated dye effluents from 165 to 564 mg/l with most of the dyes. The assessment of bioremediation products on biomodel was conducted using a fresh water fish. The liver and brain of Nile tilapia were tested to evaluate the expression of genes coding for several proteins related to stress such as metallothioneins (MTs), cytochrome P450 (CYP450), and heat shock proteins (HSPs). To assess the alterations in the gene expression, ten animals from each group were killed after 4 weeks of treatment. The results revealed significant increases in the brain and hepatic mRNA levels of all stress protein genes MT, CYP450, Hsp70a, b, and Hsp47 in the fish groups treated with industrial Direct violet, green, and brown dye water. Exposure of tilapia to bioremediation products after treatment with A. niger fungi reduced the over-expression of the stress protein genes in the brain and liver tissues.  相似文献   
973.
Recent publications by Pogge (Global ethics: seminal essays. St. Paul: Paragon House 2008) and by Singer (The life you can save: acting now to end world poverty. New York: Random House 2009) have resuscitated a debate over the justifiability of famine relief between Singer and ecologist Garrett Hardin in the 1970s. Yet that debate concluded with a general recognition that (a) general considerations of development ethics presented more compelling ethical problems than famine relief; and (b) some form of development would be essential to avoiding the problems of growth noted by Hardin. Better than renewing the debate, we should recognize two points. First, food needs do indeed evoke a moral response that is more direct and compelling than the philosophical positions often generated to rationalize a duty to bring aid. As such the argument for feeding hungry people cannot be generalized into a paradigm for development ethics without distortions that undercut the morally valid elements in Singer’s original argument. Second, contrary to prevailing assumptions in present day development ethics, food aid and famine relief continue to be important priorities for international agencies, notably the World Food Program. Emergency food assistance, the nominal topic of Singer’s original article, thus is an important issue for agricultural as well as development ethics, though one that should indeed be seen as distinct from more complex duties to address the conditions of chronic poverty and underdevelopment.  相似文献   
974.
A Carbon Cycle Science Update Since IPCC AR-4   总被引:1,自引:0,他引:1  
  相似文献   
975.
In the present work, simple-to-use predictive tool, which is simpler than current available models and involves a fewer number of parameters, requiring less complicated and shorter computations, is formulated to arrive at an appropriate estimation of the transport properties (namely viscosity and thermal conductivity) of carbon dioxide (CO2) as a function of pressure and temperature. The correlation developed accurately works for temperatures between 260 and 450 K as well as pressures between 10 and 70 MPa which is the range of pressure that is widely considered in CO2 sequestration. Results have been compared with the reported data and excellent agreement has been obtained between the predicted results and observed values. The average absolute deviations were found to be 1.1 and 1.3% for viscosity and thermal conductivity of carbon dioxide respectively. Proposed simple predictive tool and can be of immense practical value for the engineers to have a quick check on the transport properties (namely viscosity and thermal conductivity) of carbon dioxide at various temperatures and pressures without performing any experimental measurements. In particular, personnel dealing with regulatory bodies of greenhouse gas control and process industries would find the proposed approach to be user friendly involving transparent calculations with no complex expressions.  相似文献   
976.
977.
Carbon dioxide emissions have accelerated since the signing of the Kyoto Protocol. This discouraging development may partly be blamed on accelerating world growth and on lags in policy instruments. However, it also raises serious question concerning whether policies to reduce CO2 emissions are as effective as generally assumed. In recent years, a considerable number of studies have identified various feedback mechanisms of climate policies that often erode, and occasionally reinforce, their effectiveness. These studies generally focus on a few feedback mechanisms at a time, without capturing the entire effect. Partial accounting of policy feedbacks is common in many climate scenarios. The IPCC, for example, only accounts for direct leakage and rebound effects. This article attempts to map the aggregate effects of different types of climate policy feedback mechanisms in a cohesive framework. Controlling feedback effects is essential if the policy measures are to make any difference on a global level. A general conclusion is that aggregate policy feedback mechanisms tend to make current climate policies much less effective than is generally assumed. In fact, various policy measures involve a definite risk of ‘backfiring’ and actually increasing CO2 emissions. This risk is particularly pronounced once effects of climate policies on the pace of innovation in climate technology are considered. To stand any chance of controlling carbon emissions, it is imperative that feedback mechanisms are integrated into emission scenarios, targets for emission reduction and implementation of climate policy. In many cases, this will reduce the scope for subsidies to renewable energy sources, but increase the scope for other measures such as schemes to return carbon dioxide to the ground and to mitigate emissions of greenhouse gases from wetlands and oceans. A framework that incorporates policy feedback effects necessitates rethinking the design of the national and regional emission targets. This leads us to a new way of formulating emission targets that include feedback effects, the global impact target. Once the full climate policy feedback mechanisms are accounted for, there are probably only three main routes in climate policy that stand a chance of mitigating global warming: (a) returning carbon to the ground, (b) technological leaps in zero-emission energy technology that make it profitable to leave much carbon in the ground even in Annex II countries and (c) international agreements that make it more profitable to leave carbon in the ground or in forests.  相似文献   
978.
In infant period, human milk and infant formulae are the major sources of exposure to dioxins (polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (PCB). Since in many parts of Europe the mothers are increasingly reluctant to breastfeed their babies, the main objective of the present study is to assess the level of exposure of non-breast-fed infants during their early development. Consequently, the concentration levels of PCDD/F and dioxin-like PCB were determined in industrial infant formulae including "starting" (aged 0-4months) and "follow-on" (after 4months) products of milk formula, soy formula and hypoallergenic infant formula, available on the EU market. Furthermore, dietary exposure to dioxin of exclusively formula-fed infants was assessed at each month from 0 to 9months. The results suggest that dietary exposure to dioxins via formulae is higher when consuming "starting" than "follow-on" infant formulae on a body-weight basis. Estimated dietary exposure after 4months of age was always below the lowest range of the Tolerable Daily Intake (TDI) of 1pg WHO-TEQkg(-1)bwd(-1) and Provisional Tolerable Monthly Intake (PTMI) of 70pg WHO-TEQkg(-1)bwmonth(-1). The highest estimated cumulative dietary exposure to PCDD/F and dioxin-like PCB was obtained considering infants of 0-1months fed with the "starting" hypoallergenic infant formula (2.8pg WHO-TEQkg(-1)bwd(-1) and 84pg WHO-TQkg(-1)bwmonth(-1)). However, these elevated levels are much lower than those observed in some studies in breast-fed infants. The study can be used for further risk assessments in regard to infant exposure.  相似文献   
979.
Gomez CF  Constantine L  Huggett DB 《Chemosphere》2010,81(10):1189-1195
The potential for xenobiotic compounds to bioconcentrate is typically expressed through the bioconcentration factor (BCF), which has gained increased regulatory significance over the past decade. Due to the expense of in vivo bioconcentration studies and the growing regulatory need to assess bioconcentration potential, BCF is often calculated via single-compartment models, using K(OW) as the primary input. Recent efforts to refine BCF models have focused on physiological factors, including the ability of the organism to eliminate the compound through metabolic transformation. This study looks at the ability of in vitro biotransformation assays using S9 fractions to provide an indication of metabolic potential. Given the importance of the fish gill and liver in metabolic transformation, the metabolic loss of ibuprofen, norethindrone and propranolol was measured using rainbow trout (Oncorhynchus mykiss) and channel catfish (Ictalurus punctatus) gill and liver S9 fractions. Metabolic transformation rates (k(M)) were calculated and integrated into a refined BCF model. A significant difference was noted between BCF solely based on K(OW) and BCF including k(M). These studies indicate that the inclusion of k(M) in BCF models can bring predicted bioconcentration estimates closer to in vivo values.  相似文献   
980.
Phosphor imager autoradiography is a technique for rapid, sensitive analysis of the localization of xenobiotics in plant tissues. Use of this technique is relatively new to research in the field of plant science, and the potential for enhancing visualization and understanding of plant uptake and transport of xenobiotics remains largely untapped. Phosphor imager autoradiography is used to investigate the uptake and translocation of the explosives 1,3,5-trinitro-1,3,5-triazine (RDX) and 2,4,6-trinitrotoluene within Populus deltoides × nigra DN34 (poplar) and Panicum vigratum Alamo (switchgrass). In both plant types, TNT and/or TNT-metabolites remain predominantly in root tissues while RDX and/or RDX-metabolites are readily translocated to leaf tissues. Phosphor imager autoradiography is further investigated for use in semi-quantitative analysis of uptake of TNT by switchgrass.  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