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   716篇
  免费   16篇
  国内免费   12篇
安全科学   67篇
废物处理   23篇
环保管理   166篇
综合类   143篇
基础理论   174篇
污染及防治   110篇
评价与监测   35篇
社会与环境   22篇
灾害及防治   4篇
  2023年   9篇
  2022年   5篇
  2021年   13篇
  2020年   16篇
  2019年   6篇
  2018年   18篇
  2017年   21篇
  2016年   31篇
  2015年   18篇
  2014年   26篇
  2013年   49篇
  2012年   21篇
  2011年   41篇
  2010年   23篇
  2009年   32篇
  2008年   36篇
  2007年   38篇
  2006年   36篇
  2005年   38篇
  2004年   23篇
  2003年   23篇
  2002年   29篇
  2001年   18篇
  2000年   21篇
  1999年   7篇
  1998年   7篇
  1997年   8篇
  1996年   12篇
  1995年   11篇
  1994年   10篇
  1993年   6篇
  1992年   11篇
  1991年   10篇
  1990年   5篇
  1989年   2篇
  1988年   10篇
  1987年   6篇
  1986年   3篇
  1985年   4篇
  1984年   3篇
  1983年   5篇
  1982年   6篇
  1981年   10篇
  1980年   6篇
  1979年   2篇
  1977年   2篇
  1973年   1篇
  1972年   1篇
  1962年   1篇
  1956年   1篇
排序方式: 共有744条查询结果,搜索用时 140 毫秒
711.
Bedner M  Maccrehan WA 《Chemosphere》2006,65(11):2130-2137
The reactivities of the amine-containing pharmaceuticals fluoxetine and metoprolol with hypochlorite were studied using conditions that simulate wastewater disinfection including neutral pH (7.0), a range of reaction times (2–60 min), and a molar excess of hypochlorite relative to the pharmaceutical concentration (5.7 times). The reactions were monitored using liquid chromatography (LC) with several detection modes including ultraviolet absorbance (UV), mass spectrometry (MS), and post-column reaction/reductive electrochemistry (EC) for determining active chlorine products. At levels of 10 μM, both compounds reacted rapidly (<2 min) to form principally N-chloramine products that were stable in aqueous solution for at least 1 h. The reaction was also studied in wastewater, and similar reactivity was noted. These results demonstrate that the cations fluoxetine and metoprolol are likely to be rapidly transformed into neutral N-chloramines during wastewater disinfection. The reactivity of the N-chloramines was also studied with sulfite to simulate dechlorination, which is often employed in wastewater treatment. Both N-chloramines reacted slowly with sulfite. In the pure water dechlorination experiments, it was estimated that 70% and 10% of the peak areas remained after 2 min reaction time for fluoxetine and metoprolol, respectively. At longer reaction times both N-chloramines had been completely reduced by sulfite, and the product of the sulfite reduction reaction was the parent pharmaceutical amine. Since typical dechlorination times in wastewater treatment are on the order of seconds, this suggests the chloramines formed from these two basic drugs might evade dechlorination and be released into the environment. The implications of chloramine release are discussed.  相似文献   
712.
Five species of the marine insect Halobates share similar ecology but have distinct biogeographic ranges in the eastern tropical Pacific, a region from approximately 75°W–160°W and 10°S–35°N. Between 2001 and 2010, the Sea Education Association collected Halobates from 682 neuston tows (surface net 1 m × 0.5 m, 335-μm mesh) during fifteen cruises between San Diego, USA, Mexico and Tahiti. Total Halobates spp. densities varied substantially from year to year, but our data do not show a sustained change from a data set collected 40 years earlier from 1967 to 1968 (Cheng and Shulenberger in Fish Bull 78(3):579–591, 1980). Halobates are sensitive to sea surface temperature and we observed significant differences in species distributions over time, but these were not due to differences in water temperature or climate change. Our analyses show that the patterns observed are attributable to substantial but previously undescribed seasonal shifts that occur each year in the ranges for both Halobates sobrinus and Halobates micans. There is substantial overlap in ranges during seasonal shifts, but very little co-occurrence of H. sobrinus and H. micans in individual net tows, suggesting biological mechanisms rather than physical factors are restricting distribution and co-occurrence of these two species.  相似文献   
713.
The current study examines the empowering effects of transformational leaders and the extent to which these effects differ across mechanistic–organic organizational contexts. Psychological empowerment is hypothesized to provide a comprehensive motivational mechanism explaining the relationships between transformational leadership and employee job‐related behaviors. In addition, the relationships between transformational leadership, employee psychological empowerment, and job‐related behaviors are hypothesized to be stronger in organizations with more organic as opposed to mechanistic structures. Results based on a cross‐organizational sample of employees and their immediate supervisors provide support for the hypothesized relationships. Psychological empowerment mediated relationships between transformational leadership and employee task performance and organizational citizenship behaviors. The mediating role of psychological empowerment was then found to be conditional upon mechanistic–organic contexts. More specifically, organic structures enhanced, whereas mechanistic structures constrained, the empowering influence of transformational leaders. In highly mechanistic contexts, the indirect effects were no longer statistically significant. Implications for theory, research, and organizational management are discussed. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
714.
The DPSIR framework was devised in the late 1990s as a tool for the reporting and analysis of environmental problems, ranging in scale from global systems to localized watersheds. Since then, international organizations have begun to apply this framework to the evaluation of sustainable development initiatives, to better understand and overcome barriers to sustainability. While this may seem a logical application for an integrated environmental assessment tool, the use of DPSIR in sustainable development will likely perpetuate the least satisfactory outcomes of development. DPSIR cannot address the impact of aggregated, informal responses on the drivers and pressures related to environmental problems and sustainability challenges. This problem is not merely an oversight of the framework, but an issue that emerges within the structure of DPSIR itself through the unexamined, unacknowledged hierarchy of actors that this framework implicitly creates with its typology. Therefore, a DPSIR-centered approach is not a new direction for development within international organizations, but instead, a reproduction of existing inequalities between actors and stakeholders within current approaches.  相似文献   
715.
This paper presents results of a social cost–benefit analysis (CBA) of afforestation and soil moisture treatment of common lands under an integrated watershed development programme in Karnataka State, India. The aim of the study was to find out if soil moisture conservation and afforestation measures were justified in terms of economic efficiency. The assessment was undertaken by calculating the economic internal rate of return (EIRR) for five village common lands in two watersheds, Uparhalla and Chinnahagari, in central Karnataka. Focused group discussions were organised, using a semi-structured questionnaire and various stakeholders, including project implementing agencies, self help groups and other community-based organisations. The attractiveness of the programme in both watersheds for landless and land owners was high in three out of five sampled villages, with an EIRR ranging from 19% to 91%, while two villages in Chinnahagari watershed had extremely low EIRR, reflecting poor management of soil moisture and afforestation interventions and lack of institutional cohesion to sustain investments made to develop common lands. Therefore, the CBA conducted in the KAWAD project, except for two villages, shows that the investment made to develop common lands should yield substantial economic returns in the long term under a business as usual scenario.  相似文献   
716.
A contingent valuation survey was undertaken to estimate the public benefits of landscapechanges that could arise from reductions in grazing levels using the example of the Central Southern Uplands of Scotland. A dichotomous choice with continuous follow-up format was used to quantify the environmentalbenefit in terms of the willingness to pay of the general public and visitors. The paper discusses the merits of this format and the evidence of starting-point bias. In addition, the results are compared with the preferences of locals and interest groups as expressed through focus group sessions and subsets of the survey. A strong preference for more tree cover was evident, a landscape feature not well represented in the current landscape.  相似文献   
717.
We report the first positive prenatal diagnosis ofcongenital non-bullous ichthyosiform erythroderma or lamellar ichthyosis. Fetal skin samples were obtained by fetoscopy at 21 weeks' gestation and examined by light and electron microscopy. Light microscopy revealed a thickened interfollicular epidermis with multiple layers of flattened cells and excessive keratinization of the epidermal lining of the follicular infundibulum. Electron microscopy of the thickened epidermis revealed granular cells that contained larger-than-normal keratohyalin granules and multiple layers of parakeratotic cornified cells. Although there was regional variation in the degree of interfollicular keratinization, follicles from all regions showed greater and more complete keratinization, indicating that they express the abnormality early enough in development to permit prenatal diagnosis at about 20 weeks' gestation.  相似文献   
718.
Fluorescence in situ hybridization (FISH) was performed with probes specific for chromosomes 13, 18, 21, X and Y on 911 of 11123 (8.2%) amniotic fluid samples submitted to the present authors' laboratory for cytogenetic analysis over an 8-year period. Altogether 3516 hybridizations were performed with an interpretable FISH result on all chromosomes requested in 884/911 (97%) of cases. An uninformative FISH result occurred in 44 hybridizations among 27 cases (3%). Of a total of 89 karyotypically proven cases with aneuploidy that might have been detected by FISH, the overall detection rate was 84%. An inconclusive or incomplete FISH result occurred in 9/89 (10%) of these proven aneuploid cases. In the remaining 80 informative proven aneuploid cases, correct detection of aneuploidy was accomplished in 75/80 (94%) of samples. A false-negative result occurred in the remaining 5/80 (6%) of such informative cases. Eighteen cases had karyotypically proven abnormalities that could not have been detected by the targeted FISH. Aside from these 18 cases, FISH allowed correct detection of normal disomy in 785/804 (98%) of such cases. An incomplete FISH result occurred in 18 normal disomic cases. There was a single possible ‘false-positive’ FISH result for chromosome 21. Interphase FISH analysis of uncultured amniotic fluid cells has been shown to be a useful laboratory tool for rapid fetal aneuploidy screening during pregnancy. As with all clinical laboratory diagnostic tests, incomplete or inconclusive results (or even interpretive errors) occur in a small percentage of cases. Nevertheless, FISH results accompanied by other data and by appropriate counseling provide clinicians and patients with valuable information for clinical decision-making surrounding family planning and pregnancy management. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   
719.
Potential human and wildlife exposures to TCDD in landspread pulp and paper mill sludge in the State of Maine were evaluated by means of a human health and an ecological risk assessment methodology. The highest historical concentrations of TCDD reported for these sludges do not present a risk to American woodcock, selected as an indicator species for this analysis. Concentrations of TCDD as high as 50 ppt in soil are not likely to produce adverse effects in the embryonic/hatchling stage of the woodcock. This soil concentration of TCDD does not present a significant risk to sportsmen and their families that may consume birds which inhabit these sites.  相似文献   
720.
Colloidal particles in runoff may have an important role in P transfer from soils to waterbodies, but remain poorly understood. We investigated colloidal molybdate-reactive phosphorus (MRP) in surface runoff and water extracts of calcareous arable soils from the semiarid western United States. Colloidal MRP was determined by ultrafiltration and operationally defined as MRP associated with particles between 1 microm and 1 nm diameter, although a smaller pore-size filter (0.3 nm) was used to define the lower size limit of colloids in water extracts. In surface runoff from three calcareous soils generated by simulated sprinkler irrigation, colloidal MRP concentrations ranged between 0.16 and 3.07 microM, constituting between 11 and 56% of the MRP in the <1-microm fraction. Concentrations were strongly correlated with agronomic and environmental soil-test P concentrations for individual soils. Water extracts of a range of similar soils contained two size fractions of colloidal MRP: a larger fraction (1.0-0.2 microm) probably associated with fine clays, and a smaller fraction (3-0.3 nm) probably associated with Ca-phosphate minerals. Colloidal MRP was solubilized in the acidic medium of the colorimetric detection procedure, suggesting that a fraction of the filterable MRP in runoff from calcareous soils may not be as readily bioavailable as free phosphate in waterbodies. Our results suggest that colloidal MRP is an important but poorly understood component of P transfer in runoff from calcareous western U.S. soils and should be given greater consideration in mechanistic studies of the P transfer process.  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