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   17520篇
  免费   129篇
  国内免费   73篇
安全科学   407篇
废物处理   652篇
环保管理   1960篇
综合类   5444篇
基础理论   3609篇
环境理论   2篇
污染及防治   4093篇
评价与监测   877篇
社会与环境   616篇
灾害及防治   62篇
  2018年   200篇
  2017年   188篇
  2016年   294篇
  2015年   224篇
  2014年   325篇
  2013年   1159篇
  2012年   373篇
  2011年   522篇
  2010年   493篇
  2009年   556篇
  2008年   579篇
  2007年   600篇
  2006年   528篇
  2005年   469篇
  2004年   506篇
  2003年   461篇
  2002年   446篇
  2001年   616篇
  2000年   418篇
  1999年   290篇
  1998年   207篇
  1997年   199篇
  1996年   197篇
  1995年   233篇
  1994年   242篇
  1993年   211篇
  1992年   224篇
  1991年   236篇
  1990年   256篇
  1989年   229篇
  1988年   181篇
  1987年   180篇
  1986年   180篇
  1985年   180篇
  1984年   199篇
  1983年   187篇
  1982年   195篇
  1981年   207篇
  1980年   169篇
  1979年   180篇
  1978年   147篇
  1977年   139篇
  1974年   147篇
  1973年   146篇
  1968年   156篇
  1967年   184篇
  1966年   154篇
  1965年   148篇
  1964年   151篇
  1963年   139篇
排序方式: 共有10000条查询结果,搜索用时 22 毫秒
711.
712.
713.
The fast growing of global aquaculture industry accompanied with increasing pressure on the supply and price of traditional feed materials (e.g., fish meal and soy bean meal). This circumstance has urged the need to search alternative sources of feed stuff. Food waste was used as feed stuff in rearing fish which possess substantial protein and lipid. Grass carp are major species reared in Hong Kong with lower nutritional requirements; it is also an ideal species for investigating the feasibility of using food waste as fish feeds for local aquaculture industry. The growth and immunity, reflected by total protein, total immunologlobulin (IgI), and nitroblue tetrazolium (NBT) activity of grass carp blood, were depressed when feeding with food waste feeds without enzymes. However, the supplementation of bromelain and papain in fish feed enhanced the efficient use of food waste by grass carp, which in turn improved the fish immunity. The present results indicated that the addition of those enzymes could enhance the feed utilization by fish and hematological parameters of grass carp, and the improvement on growth and immunity superior to the control (commercial feed) was observed with the addition of bromelain and papain supplement. Addition of 1 and 2 % mixture of bromelain and papain could significantly enhance the lipid utilization in grass carp.  相似文献   
714.
The main objectives of this work were to identify and determine the concentrations of polycyclic aromatic hydrocarbons (PAHs) and trace metals in carpet dust samples from various mosques of the city of Riyadh and to assess the health risks associated with the exposure to these pollutants. Therefore, 31 samples of mosque’s carpet dust from Riyadh were collected. The results showed that 14 PAHs were present in the dust samples with concentrations ranged from 90 to 22,146 ng g?1 (mean = 4096 ± 4277 ng g?1) where low molecular weight compounds were dominant. The presence of PAHs were in the order of naphthalene > chrysene and benzo(b)fluoranthene > benzo(a)pyrene > acenaphthene and benzo(k)fluoranthene > pyrene and the absence of indeno(1,2,3-cd)pyrene and dibenz(a,h)anthracene. The diagnostic ratio coupled with principle component analysis (PCA) revealed mix sources of petrogenic from traffic, stack emission, and pyrogenic inputs from essence and perfumed wood burning. Trace metals were significant in the dust samples, and their concentrations decrease in the order of Zn, Mn, Cu, Cr, Pb, Ni, and V where Zn being the highest (94.4 ± 91.5 μg g?1) and indium was the lowest (1.9 ± 9.3 μg g?1). The trace metals were major in southern and central parts of Riyadh and followed the order of central Riyadh > southern Riyadh > western Riyadh > eastern Riyadh > northern Riyadh. Estimated risk based on the total PAHs was found to be 4.30 × 10?11 for adult and 1.56 × 10?11 for children. Elemental non-cancer risk for adults ranged from 7.9 × 10?4 for Co to 7.58 × 10?1 for Li and for children ranged from 3.70 × 10?3 for Co to 3.54 for Li. Policy implication and mitigations of PAHs in Riyadh and Saudi Arabia were highlighted.  相似文献   
715.
The gain and loss rates and the biological half-life of polychlorinated biphenyls (PCBs) and p,p'-DDE in wild birds were calculated using the values on burdens of these compounds in the bodies of adelie penguins in a previous report (Subramanian et al., 1986). The daily loss rate of PCBs (0.26%) was found to be higher than DDT compounds (0.12%) resulting in the longer biological half-life of the latter compounds (580 days) than PCBs (270 days). Hence, once DDT compounds are absorbed they are more persistent in the organisms' bodies due to their high lipophilicity and comparatively less metabolisable nature than PCBs.  相似文献   
716.
The leaching behavior of selected four- to six-ring polycyclic aromatic hydrocarbons (PAH) from a tumorigenic coal-derived solid product was determined using three media to evaluate their potential bioavailabilities. Equilibrium PAH concentrations generally exceeded the aqueous solubilities after less than five days of leaching. PAH selectively accumulated in phospholipid vesicles at individual concentrations greater than 1 μg/g, which is ca. 100-fold over that in the bulk aqueous leachate. The results suggest that the PAH are quite bioavailable from the solid product, and that cell membranes can be exposed to considerable quantities of these PAH over an extended bioassay.  相似文献   
717.
Airborne particulate matter (PM10, PM2.5, PM1) and volatile organic compounds (benzene, toluene, m,p-xylene, o-xylene) samples were collected during winter and summer seasons of 2005 at two sites, representing an urban and a suburban region of the Greater Athens Area. Urban site traffic emissions were the major contributor to the concentration of PM2.5, PM10, toluene, and xylenes, while benzene and PM1 concentrations were presented in significant spatial variations. K+, Na+, Mg2+, Ca2+, NO3-, Cl- and SO42- ions were analyzed for the chemical characterization of the collected PM samples. The results showed that Na+ cations and SO42- anions were the dominant species, during winter and summer, respectively, in both sites. The analysis of the synoptic scale and mesoscale atmospheric circulation during the experimental periods demonstrated that the meteorological conditions play a key role, not only in the variation but also in the distribution of the ionic concentrations at the three fractions of particulates and the dominant character (alkaline/acidic/neutral) of the particulates at the two sampling sites.  相似文献   
718.
The abundance and relevance ofAccumulibacter phosphatis (presumed to be polyphosphate-accumulating organisms [PAOs]), Competibacter phosphatis (presumed to be glycogen-accumulating organisms [GAOs]), and tetrad-forming organisms (TFOs) to phosphorus removal performance at six full-scale enhanced biological phosphorus removal (EBPR) wastewater treatment plants were investigated. Coexistence of various levels of candidate PAOs and GAOs were found at these facilities. Accumulibacter were found to be 5 to 20% of the total bacterial population, and Competibacter were 0 to 20% of the total bacteria population. The TFO abundance varied from nondetectable to dominant. Anaerobic phosphorus (P) release to acetate uptake ratios (P(rel)/HAc(up)) obtained from bench tests were correlated positively with the abundance ratio of Accumulibacter/(Competibacter +TFOs) and negatively with the abundance of (Competibacter +TFOs) for all plants except one, suggesting the relevance of these candidate organisms to EBPR processes. However, effluent phosphorus concentration, amount of phosphorus removed, and process stability in an EBPR system were not directly related to high PAO abundance or mutually exclusive with a high GAO fraction. The plant that had the lowest average effluent phosphorus and highest stability rating had the lowest P(rel)/HAc(up) and the most TFOs. Evaluation of full-scale EBPR performance data indicated that low effluent phosphorus concentration and high process stability are positively correlated with the influent readily biodegradable chemical oxygen demand-to-phosphorus ratio. A system-level carbon-distribution-based conceptual model is proposed for capturing the dynamic competition between PAOs and GAOs and their effect on an EBPR process, and the results from this study seem to support the model hypothesis.  相似文献   
719.
Releases of ammonia (NH3) to the atmosphere contribute significantly to the deposition of nitrogen to both terrestrial and aquatic ecosystems. This is the background for the national NH3 emission ceilings in Europe. However, in some countries the national legislation aims not only to meet these ceilings but also to reduce the atmospheric nitrogen deposition to local ecosystems. Such measures to reduce the load of nitrogen to local ecosystems were introduced in Denmark in 1994. In this paper we demonstrate that this regulation is reflected in the NH3 concentrations in Denmark. The Danish legislation forces farmers to applying manure to the fields during the crop-growing season. We have analyzed the seasonal variation in local NH3 concentrations over the time period of 1989-2003. During this period the seasonal variation has changed from having moderate spring and autumn concentration peaks to having a single and much more pronounced spring peak. In the analysis we apply an NH3 emission model to demonstrate that these changes in the seasonal variation are a result of the changes in the Danish legislation. The analysis demonstrates the strength of using a high-resolution emission model in the analysis of routine monitoring data.  相似文献   
720.
In this paper, the first data on brominated flame retardants (BFRs), in particular polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecane (HBCD) in eggs of bird species from South Africa are described (N=43). Concentrations of PBDEs were detected in all the studied species and in all the geographic areas. Highest concentrations of PBDEs were measured in bird eggs from the Vaal River, which is situated downstream of the most industrialized area in South Africa. Sum-PBDE concentrations were highest in eggs of one African sacred ibis (396 ng g(-1) lipid weight (lw)), possibly due to foraging on dumping sites. Lowest mean level of sum-PBDEs (2.3 ng g(-1) lw) was measured in cattle egrets (N=11) from Barberspan Sanctuary, a Ramsar site. The PBDE congener pattern showed large differences, reflecting different trophic levels, migratory behavior, distance to the source, and, exposure to different PBDE mixtures, among others. HBCD was detected only in four species, and highest levels were measured in one egg of African sacred ibis (71 ng g(-1) lw). In most species, levels of PBDEs were one to several orders of magnitude lower than levels of DDTs and PCBs. PBDEs correlated strongly with DDTs, PCBs and some other organochlorines (OCs), indicating the same source. The widespread occurrence of PBDEs in the South African avian species showed a strong need for further investigations of PBDEs in the Southern African environment.  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