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   583篇
  免费   13篇
  国内免费   7篇
安全科学   14篇
废物处理   38篇
环保管理   43篇
综合类   65篇
基础理论   156篇
污染及防治   187篇
评价与监测   54篇
社会与环境   44篇
灾害及防治   2篇
  2023年   7篇
  2022年   20篇
  2021年   14篇
  2020年   8篇
  2019年   12篇
  2018年   26篇
  2017年   27篇
  2016年   34篇
  2015年   14篇
  2014年   32篇
  2013年   49篇
  2012年   42篇
  2011年   56篇
  2010年   34篇
  2009年   41篇
  2008年   29篇
  2007年   34篇
  2006年   24篇
  2005年   26篇
  2004年   16篇
  2003年   15篇
  2002年   4篇
  2001年   8篇
  2000年   9篇
  1999年   2篇
  1997年   3篇
  1996年   3篇
  1993年   3篇
  1992年   1篇
  1991年   3篇
  1990年   2篇
  1989年   1篇
  1988年   1篇
  1986年   1篇
  1979年   1篇
  1972年   1篇
排序方式: 共有603条查询结果,搜索用时 15 毫秒
561.

Objective

In gastroschisis, there is evidence to suggest that gut dysfunction develops secondary to bowel inflammation; we aimed to evaluate the effect of maternal antenatal corticosteroids administered for obstetric reasons on time to full enteral feeds in a multicenter cohort study of gastroschisis infants.

Methods

A three center, retrospective cohort study (1992-2013) with linked fetal/neonatal gastroschisis data was conducted. The primary outcome measure was time to full enteral feeds (a surrogate measure for bowel function) and secondary outcome measure was length of hospital stay. Analysis included Mann-Whitney and Cox regression.

Results

Of 500 patients included in the study, 69 (GA at birth 34 [25-38] weeks) received antenatal corticosteroids and 431 (GA at birth 37 [31-41] weeks) did not. Antenatal corticosteroids had no effect on the rate of reaching full feeds (Hazard ratio HR 1.0 [95% CI: 0.8-1.4]). However, complex gastroschisis (HR 0.3 [95% CI: 0.2-0.4]) was associated with an increased time to reach full feeds and later GA at birth (HR 1.1 per week increase in GA [95% CI: 1.1-1.2]) was associated with a decreased time to reach full feeds.

Conclusion

Maternal antenatal corticosteroids use, under current antenatal steroid protocols, in gastroschisis is not associated with an improvement in neonatal outcomes such as time to full enteral feeds or length of hospital stay.  相似文献   
562.
Firn core methanesulphonic acid (MSA) stratigraphy from Talos Dome (East Antarctica) was compared with anomalies of the satellite-measured sea ice extent (1973–1995) in the Ross Sea and Wilkes Land oceanic sector. In spite of the sparseness of sea ice data, the MSA maxima fit with many positive sea ice anomalies in the Ross Sea. This evidence suggests that marine biogenic activity enhanced by large sea ice cover is an important, but not exclusive, factor in controlling MSA concentration in snow precipitation at Talos Dome. Other than source intensity, differences in regional atmospheric transport mechanisms affect the arrival of MSA-rich aerosol at Talos Dome. To clarify the role of transport processes in bringing biogenic aerosol to Talos Dome, a spectral analysis was applied to the MSA, SOI (South Oscillation Index), and SAM (Southern Annular Mode) record. Synchronicity or phase shift between the chemical signature and atmospheric circulation modes were tested. The variations in the MSA profile have a periodicity of 6.9, 4.9, 3.5, and 2.9 years. The 6.9 and 2.9 year periodicities show a strong positive correlation and are synchronous with corresponding SOI periodicity. This variability could be related to an increase in MSA source intensity (by dimethylsulphide from phytoplanktonic activity) linked to the sea ice extent in the Ross Sea area, but also to an increased strength in transport processes. Both of these factors are correlated with La Niña events (SOI positive values). Furthermore, SAM positive values are related to an increased sea ice extent in the Ross Sea sector and show two main periodicities 3.3 and 3.8 years. These periodicities determine the MSA variability at 3.5 years. However, the effect of intensification of the polar vortex and the consequent reduction in transport process intensity, which reduce the delivery of air masses enriched in MSA from oceanic areas to Talos Dome, make the effect of the SAM on the MSA concentration at Talos Dome less active than the SOI. In this way, snow deposition at the Talos Dome records larger MSA concentration by the combined effects of increased source emissions and more efficient transport processes. The MSA record from Talos Dome can therefore be considered a reliable proxy of sea ice extent when the effect of changes in transport processes in this region of Antarctica is considered. Over the previous 140 years, these conditions occur with a periodicity of 6.9 years.  相似文献   
563.
Wastewaters are a source of pathogenic micro-organisms in the environment. The microbial load and residues found in the final effluents of wastewater-treatment plants (WWTPs) depend on the WWTPs' abatement capacity and the final disinfection treatment systems applied to wastewaters before discharge into water. A historical database with data on surface and marine-coastal water quality and on the characterization of WWTP effluents was made using data from 1997 to 2004 to assess the microbiologic impact along the coast of the Venice province (Italy, northern Adriatic sea). The monitoring of river and sea discharges along the coast is integrated with the application of the Synthetic Pluriennal Faecalization Index (ISPF). The experimental study was conducted in the period from November 2002 to April 2004 by the Veneto Regional Environmental Prevention and Protection Agency. The results of this investigation on faecal contamination together with previous data are presented with a preliminary performance characterization of the WWTPs' disinfection technologies (sodium hypochlorite, peracetic acid, UV rays, and ozone).  相似文献   
564.
The EMAS Regulation (Reg 761/01 EC) is EU scheme implemented by the European Commission since 1993 and it is for the implementation of an Environmental Management System (EMS) by any organization. The EMS was originally proposed by the European Commission and by the ISO as the frontrunner of a series of policy tools that enable companies to simultaneously pursue environmental objectives and competitive targets in a synergetic way.Based on the unique dataset of the EVER project, this paper investigates whether or not an EMS implemented within the EMAS Regulation has any effect on firm performance both from an environmental and a competitive point of view. Our econometric analysis shows the positive impact of a well-designed environmental management system on environmental performance and, as a consequence, on technical and organizational innovations. Effects on other competitive variables such as market performance, resource productivity and intangible assets are not strongly supported.  相似文献   
565.
566.
The present work proposes a siting process for the detection of a suitable site for wave energy exploitation. The choice of a suitable site is based on the good agreement between energy availability, environmental sustainability, and equipped facilities to exploit wave energy. The case study in the northern Latium coast is explicative because in this area there are several activities that affect marine ecosystems, and the introduction of renewable energies promote the reduction of anthropic pressures. The nearshore wave power is studied through the numerical wave model (CMS-Wave), and available wave buoys along the coast were used to compare numerical results. In correspondence with Civitavecchia harbour, the largest nearshore wave energy was found; the large depth in front of the breakwater allows to conserve a great part of offshore wave power, with an average dissipation rate of 10 % less than offshore, with mean annual available wave energy of 25.4 MWh/m and seasonal fluctuation of 5.4 MWh/m. This area appears to be an optimal site for nearshore and shoreline wave energy device tests and installations, for energy availability (intermediate level respect Mediterreanean Sea), low potential environmental impact, easier accessibility, and policy oriented towards a larger sustainability of harbour activities.  相似文献   
567.
SUMMARY

Studying the interactions among ecological factors and economic performance measured at the local scale is necessary to suggest policies able to mitigate natural resource depletion in complex ecosystems, like those in the Mediterranean region. The aim of this paper is to explore the relationship among natural resource depletion due to land degradation (LD) and some economic characteristics of local labour systems in Italy, a country where many areas, especially southern regions, are vulnerable. LD was estimated using an environmental sensitive area index, covering the national territory at a fine scale, which takes into account ecological factors such as climate, soil and vegetation. Economic indicators used here consider per capita income, land productivity, production and labour productivity by sector (agriculture, industry and services). A regression analysis was built-up at the LLS scale using an index change over time (1990–2000) as dependent variable and economic variables as predictors. A principal component analysis (PCA) was carried out to synthesise the outputs of the regression analysis. Results indicate a negative relationship among per capita income and LD over the whole study area. However, other variables showed a significant correlation with the dependent variable, highlighting the importance of local factors to increase land vulnerability. In order to clarify the contribution of economic factors to natural resource depletion it is necessary to drive integrate policies to combat LD in dry Mediterranean areas.  相似文献   
568.
569.
We investigated the influence of the mineralogical composition of marine sediments on bacterial activity in experimental microcosms. Calcite and quartz were added to natural marine sediments and microbial response in terms of total bacterial abundance and biomass, β-D-glucosidase exo-enzymatic activity and bacterial incorporation of a radio-labelled (3H-leucine) substrate were investigated for a period of one month. We report here that after 15 days the mineralogical composition of the sediment (calcite vs. quartz) had an impact on bacterial abundance and activity (reduced for ca 15% and 56%, respectively). However, such impact was mitigated or even disappeared in high organic nutrient conditions.  相似文献   
570.
Sperm storage is widespread in many vertebrate groups, and it is frequently associated with promiscuous mating systems. Chelonian species are one of the most outstanding examples of a promiscuous group capable of long-term sperm storage; specialized structures have evolved within the oviducts of these vertebrates to ensure sperm vitality across reproductive cycles. Thus far, few studies have investigated the factors regulating multiple paternity, sperm usage by females and paternity distribution in successive clutches. This study aimed to investigate the effect of mating order on male mounting and reproductive success in Testudo hermanni hermanni, combining behavioural and genetic data. A series of planned matings were performed, within which experimental females were mated sequentially to two different males under controlled conditions. Observations conducted during experimental matings revealed that courtship displays did not significantly differ between the first and second males to mate with a female. Interactions ending with a mount were characterized by a significantly higher intensity and occurrence of determinate courtship behaviours, for example biting and running after the female. Paternity analysis performed on hatchlings produced from experimental females revealed that 46 % of the clutches were multi-sired. A significant contribution of previous years' partners was still found, thus confirming the long-term sperm storage within the female oviduct in this species. Finally, mating order did not significantly affect the reproductive success of experimental males during the on-going reproductive season.  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