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   5350篇
  免费   39篇
  国内免费   56篇
安全科学   88篇
废物处理   344篇
环保管理   384篇
综合类   859篇
基础理论   1140篇
环境理论   5篇
污染及防治   1791篇
评价与监测   471篇
社会与环境   349篇
灾害及防治   14篇
  2023年   55篇
  2022年   169篇
  2021年   130篇
  2020年   51篇
  2019年   64篇
  2018年   200篇
  2017年   125篇
  2016年   229篇
  2015年   154篇
  2014年   261篇
  2013年   497篇
  2012年   278篇
  2011年   299篇
  2010年   246篇
  2009年   205篇
  2008年   297篇
  2007年   287篇
  2006年   253篇
  2005年   184篇
  2004年   196篇
  2003年   171篇
  2002年   133篇
  2001年   160篇
  2000年   86篇
  1999年   57篇
  1998年   29篇
  1997年   24篇
  1996年   17篇
  1995年   43篇
  1994年   22篇
  1993年   20篇
  1992年   22篇
  1991年   16篇
  1990年   21篇
  1989年   19篇
  1985年   14篇
  1975年   12篇
  1972年   13篇
  1966年   15篇
  1965年   20篇
  1964年   29篇
  1963年   13篇
  1962年   17篇
  1961年   12篇
  1960年   12篇
  1959年   27篇
  1958年   25篇
  1957年   19篇
  1956年   15篇
  1955年   18篇
排序方式: 共有5445条查询结果,搜索用时 15 毫秒
971.
A study has been made of the presence and reactivity of the most commonly used surfactants, both anionic (linear alkylbenzene sulfonates, LAS, and alkyl ethoxysulfates, AES) and non-ionic (alcohol polyethoxylates, AEOs, and nonylphenol polyethoxylates, NPEOs), in water and surface sediments from the middle stretch of the Guadalete River in SW Spain (12 stations). Average values were between 0.1 and 3.7 mg kg(-1) in sediment, and between 0.2 and 37 μg L(-1) in water. The sorption of surfactants was dominated by hydrophobic mechanisms, so those homologues having longer alkyl chains (e.g. C(18)AEO) showed higher relative percentages and concentrations in sediments compared with water. Local and sharply higher concentrations of these compounds were observed at three sampling stations (7, 9 and 12), indicating the occurrence of wastewater discharges into the river. By analysing the distributions of different surfactant homologues and their metabolites we were able to distinguish between sewage contamination from sources discharging treated and untreated wastewaters. Upstream (stations 1-2), LAS concentrations were below 30 μg L(-1) and the composition of their degradation intermediates (sulfophenyl carboxylic acids, SPCs) (160 μg L(-1)) was dominated by short-chain homologues (C(6)-C(9)SPCs), indicating that the degradation of this surfactant is at an advanced stage. The highest concentration (487 μg L(-1)) of SPCs was detected near the effluent outlet of a sewage treatment plant (STP) (station 12). Sampling stations (7 and 9) affected by untreated wastewater discharges were the only ones showing the presence of the most reactive and biodegradable SPC isomers and homologues (e.g. C(11)SPC). Here, LAS reached the highest concentration values measured (>2 mg L(-1)), and showed a homologue distribution closer to that of commercial mixtures than LAS found at the other stations.  相似文献   
972.

Objective

Omphalocele is known to be associated with genetic anomalies like trisomy 13, 18 and Beckwith–Wiedemann syndrome, but not with Turner syndrome (TS). Our aim was to assess the incidence of omphalocele in fetuses with TS, the phenotype of this association with other anomalies, their karyotype, and the fetal outcomes.

Method

Retrospective multicenter study of fetuses with confirmed diagnosis of TS. Data were extracted from a detailed questionnaire sent to specialists in prenatal ultrasound.

Results

680 fetuses with TS were included in this analysis. Incidence of small omphalocele in fetuses diagnosed ≥12 weeks was 3.1%. Including fetuses diagnosed before 12 weeks, it was 5.1%. 97.1% (34/35) of the affected fetuses had one or more associated anomalies including increased nuchal translucency (≥3 mm) and/or cystic hygroma (94.3%), hydrops/skin edema (71.1%), and cardiac anomalies (40%). The karyotype was 45,X in all fetuses. Fetal outcomes were poor with only 1 fetus born alive.

Conclusion

TS with 45,X karyotype but not with X chromosome variants is associated with small omphalocele. Most of these fetuses have associated anomalies and a poor prognosis. Our data suggest an association of TS with omphalocele, which is evident from the first trimester.  相似文献   
973.
We report a fetus with hydrops, congenital heart disease and bilateral radioulnar synostosis caused by a novel pathogenic MECOM variant. The female fetus was referred for post-mortem examination after fetal hydrops and intrauterine death was diagnosed at 20 weeks gestation. Post-mortem examination confirmed fetal hydrops, pallor, truncus arteriosus and bilateral radioulnar synostosis. Trio whole genome sequencing analysis detected a novel de novo heterozygous pathogenic loss-of-function variant in MECOM (NM_004991), associated with a diagnosis of Radioulnar Synostosis with Amegakaryocytic Thrombocytopenia 2 (RUSAT-2). RUSAT-2 is a variable condition associated postnatally with bone marrow failure, radioulnar synostosis and congenital anomalies. RUSAT-2 is not currently associated with a prenatal phenotype or fetal demise, and was not present on diagnostic NHS prenatal gene panels at time of diagnosis. This case highlights the diagnostic value of detailed phenotyping with post-mortem examination, and of using a broad sequencing approach.  相似文献   
974.
975.
Food and Environmental Virology - Norovirus is a major cause of foodborne-associated acute gastroenteritis (AGE) outbreaks worldwide. Usually, food products are contaminated either during...  相似文献   
976.
Food and Environmental Virology - Enteric viruses have been described as important contaminants in fresh and ready-to-eat foods such as sandwiches, deli meat and dairy products. This is a...  相似文献   
977.
Energy recovery from grass using two-phase anaerobic digestion   总被引:9,自引:0,他引:9  
Municipal solid wastes are major sources of air, water and soil contamination. There is a need for alternative waste management techniques to better utilize the waste and minimize its adverse environmental impact. A two-phase pilot-scale bio-fermentation system was used to evaluate the feasibility of producing methane from grass waste, a major constituent of solid wastes. The bi-phasic system consists of a solid phase and a methane phase. Leachate is re-circulated through the solid phase until a desired level of volatile fatty acid (VFA) is accumulated in the leachate. The leachate is then transferred to the methane reactor where the VFA is converted to methane. The results showed that 67% of the volatile solids in the waste can be converted into soluble chemical oxygen demand in a period of six months. The system produced an average of 0.15 m3 of methane per kg of grass. The average methane concentration in the produced gas was 71%. A mathematical model was developed to estimate the methane and carbon dioxide concentrations in the gas phase as a function of reactor properties.  相似文献   
978.
Leaching of metals from fly ashes in the presence of complexing agents   总被引:3,自引:0,他引:3  
The leachability of some metals (Al, As, Ba, Ca, Cr, Cu, Fe, K, Mg, Mn, Ti, Zn) from fly ashes was studied in the presence of ethylenediamine tetraacetic acid (EDTA) and naturally occurring complexing agents-humic acids (HAs). Secondary complex-forming equilibria taking place in the leachates increase significantly the leached amounts of most metals. Kinetic experiments showed that almost the whole "available" amounts of metals are leached from fly ash within a time period of several hours (mostly within 20 h), with exceptions of matrix constituents (typically aluminium), which are released more slowly.  相似文献   
979.
Journal of Material Cycles and Waste Management - Biofilters have been recognized as a key technology in the mitigation of greenhouse gases (GHG) emitted by landfills. This study aimed to evaluate...  相似文献   
980.
Journal of Material Cycles and Waste Management - Solid waste management is the main topic of the circular economy and remains a challenge for public management, because despite the recent economic...  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