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   10772篇
  免费   1346篇
  国内免费   5677篇
安全科学   1930篇
废物处理   424篇
环保管理   1011篇
综合类   9362篇
基础理论   2074篇
环境理论   2篇
污染及防治   1615篇
评价与监测   766篇
社会与环境   362篇
灾害及防治   249篇
  2024年   58篇
  2023年   419篇
  2022年   595篇
  2021年   671篇
  2020年   667篇
  2019年   691篇
  2018年   547篇
  2017年   522篇
  2016年   630篇
  2015年   720篇
  2014年   644篇
  2013年   1162篇
  2012年   1113篇
  2011年   1203篇
  2010年   783篇
  2009年   936篇
  2008年   787篇
  2007年   905篇
  2006年   889篇
  2005年   639篇
  2004年   560篇
  2003年   471篇
  2002年   353篇
  2001年   304篇
  2000年   277篇
  1999年   218篇
  1998年   176篇
  1997年   177篇
  1996年   131篇
  1995年   123篇
  1994年   85篇
  1993年   79篇
  1992年   52篇
  1991年   22篇
  1990年   24篇
  1989年   21篇
  1988年   14篇
  1987年   8篇
  1986年   11篇
  1985年   4篇
  1984年   7篇
  1983年   12篇
  1982年   13篇
  1981年   9篇
  1980年   6篇
  1979年   4篇
  1978年   4篇
  1973年   5篇
  1972年   5篇
  1971年   33篇
排序方式: 共有10000条查询结果,搜索用时 546 毫秒
351.
Subsistence hunting presents a conservation challenge by which biodiversity preservation must be balanced with safeguarding of human livelihoods. Globally, subsistence hunting threatens primate populations, including Madagascar's endemic lemurs. We used population viability analysis to assess the sustainability of lemur hunting in Makira Natural Park, Madagascar. We identified trends in seasonal hunting of 11 Makira lemur species from household interview data, estimated local lemur densities in populations adjacent to focal villages via transect surveys, and quantified extinction vulnerability for these populations based on species-specific demographic parameters and empirically derived hunting rates. We compared stage-based Lefkovitch with periodic Leslie matrices to evaluate the impact of regional dispersal on persistence trajectories and explored the consequences of perturbations to the timing of peak hunting relative to the lemur birth pulse, under assumptions of density-dependent reproductive compensation. Lemur hunting peaked during the fruit-abundant wet season (March–June). Estimated local lemur densities were roughly inverse to body size across our study area. Life-history modeling indicated that hunting most severely threatened the species with the largest bodies (i.e., Hapalemur occidentalis, Avahi laniger, Daubentonia madagascariensis, and Indri indi), characterized by late-age reproductive onsets and long interbirth intervals. In model simulations, lemur dispersal within a regional metapopulation buffered extinction threats when a majority of local sites supported growth rates above the replacement level but drove regional extirpations when most local sites were overharvested. Hunt simulations were most detrimental when timed to overlap lemur births (a reality for D. madagascariensis and I. indri). In sum, Makira lemurs were overharvested. Regional extirpations, which may contribute to broad-scale extinctions, will be likely if current hunting rates persist. Cessation of anthropogenic lemur harvest is a conservation priority, and development programs are needed to help communities switch from wildlife consumption to domestic protein alternatives.  相似文献   
352.
ABSTRACT

Sketch-map-facilitated interviews were conducted in 23 villages in two adjacent regions in the southern Yucatan Peninsula of Mexico – the Maya (and increasingly Mennonite) forest-agriculture mosaic of the Chenes, and the late-20th-century-settlement forest frontier of Calakmul – to determine the frequency and typology of local-scale reserves, including the external (e.g. Payments for Environmental Services programs) and internal sources of their generation. 9% of the study communities are found to satisfy the author’s criteria for deliberate, autochthonous reserves. The static polygon reserve and static map are found to have limited value for understanding the evolving cultural ecologies of these regions. Alternative approaches are discussed, particularly those employed by geographers.  相似文献   
353.
• Isotope dilution method was developed for the determination of 27 PPCPs in water. • The established method was successfully applied to different types of water samples. • The correction effect of corresponding 27 ILSs over 70 d was investigated. • Benefit of isotopic dilution method was illustrated for three examples. Pharmaceuticals and personal care products (PPCPs) are a unique group of emerging and non-persistent contaminants. In this study, 27 PPCPs in various water samples were extracted by solid phase extraction (SPE), and determined by isotope dilution method using liquid chromatography coupled to tandem triple quadruple mass spectrometer (LC-MS/MS). A total of 27 isotopically labeled standards (ILSs) were applied to correct the concentration of PPCPs in spiked ultrapure water, drinking water, river, effluent and influent sewage. The corrected recoveries were 73%–122% with the relative standard deviation (RSD)<16%, except for acetaminophen. The matrix effect for all kinds of water samples was<22% and the method quantitation limits (MQLs) were 0.45–8.6 ng/L. The developed method was successfully applied on environmental water samples. The SPE extracts of spiked ultrapure water, drinking water, river and wastewater effluent were stored for 70 days, and the ILSs-corrected recoveries of 27 PPCPs were obtained to evaluate the correction ability of ILSs in the presence of variety interferences. The recoveries of 27 PPCPs over 70 days were within the scope of 72%–140% with the recovery variation<37% in all cases. The isotope dilution method seems to be of benefit when the extract has to be stored for long time before the instrument analysis.  相似文献   
354.
This study proposes an improved integrated water resource management (IWRM), in which water conservation was analyzed for the entire water use process. A multi-objective optimization method was applied to optimize the IWRM, which investigated the reduction of freshwater consumption and the total water supply cost. Customer's preference for saving water and an end use analysis (EUA) was applied in the water conservation analysis. Taking Tianjin as the study area, a reduction in customer's economic pressure (EP) was utilized to evaluate the degree of the customer's preference for saving water. The results revealed that agriculture had a greater preference for saving water than other sectors, where as the public had the weakest motivation for saving water. Improving the transportation method could contribute 62.1% of the total water savings in the agriculture sector. The optimization of the IWRM demonstrated that the local freshwater savings would be 21.5%, and the total cost for water supplies would decrease by 13%. However, a government subsidy of 87.5 million Yuan would be needed. Additionally, by analyzing the change in the amount of water savings affected by water price, the appropriate water price increase range was suggested to be 1.5–1.7 times the original price.  相似文献   
355.
Upcycling polymer wastes into useful, and valuable carbon based materials, is a challenging process. We report a novel catalyst-free and solvent-free technique for the formation of nano channeled ultrafine carbon tubes (NCUFCTs) and multiwalled carbon nanotubes (MWCNTs) from polyethylene terephthalate (PET) wastes, using rotating cathode arc discharge technique. The soot obtain from the anode contains ultrafine and nano-sized solid carbon spheres (SCS) with a mean diameter of 221 nm and 100 nm, respectively, formed at the lower temperature region of the anode where the temperature is approximately 1700 °C. The carbon spheres are converted into long “Y” type branched and non-branched NCUFCTs and MWCNTs at higher temperature regions where the temperature is approximately 2600 °C, with mean diameters of 364 nm and 95 nm, respectively. Soot deposited on the cathode is composed of MWCNTs with a mean diameter of 20 nm and other nanoparticles. The tubular structures present in the anode are longer, bent and often coiled with lesser graphitization compared to the nanotubes in the soot on the cathode.  相似文献   
356.
Fresh leachate, generated in municipal solid waste incineration (MSWI) plants, contains various pollutants with extremely high strength organics, which usually requires expensive and complex treatment processes. This study investigated the feasibility of blending treatment of MSWI leachate with municipal wastewater. Fresh MSWI leachate was pretreated by coagulation–flocculation with FeCl3 2 g/L and CaO 25 g/L, plate-and-frame filter press, followed by ammonia stripping at pH above 12. After that, blending treatment was carried out in a full-scale municipal wastewater treatment plant (WWTP) for approximately 3 months. Different operational modes consisting of different pretreated leachate and methanol addition levels were tested, and their performances were evaluated. Results showed that throughout the experimental period, monitored parameters in the WWTP effluent, including COD (<60 mg/L), BOD5 (<20 mg/L), ammonium (<8 mg/L), phosphorus (<1.5 mg/L) and heavy metals, generally complied with the Chinese sewage discharged standard. Under the experimental conditions, a certain amount of methanol was needed to fulfill TN removal. An estimation of the operation cost revealed that the expenditure of blending treatment was much lower than the total costs of respective treatment of MSWI leachate and municipal wastewater. The outcomes indicated that blending treatment could not only improve the treatability of the MSWI leachate, but also reduce the treatment cost of the two different wastewaters.  相似文献   
357.
A CFD scheme was presented for modeling municipal solid waste (MSW) combustion in a moving-grate incinerator, including the in-bed burning of solid wastes, the out-of-bed burnout of gaseous volatiles, and the selective non-catalytic reduction (SNCR) process between urea (CO(NH2)2) and NOx. The in-bed calculations provided 2-D profiles of the gas–solid temperatures and the gas species concentrations along the bed length, which were then used as inlet conditions for the out-of-bed computations. The over-bed simulations provided the profiles of incident radiation heat flux on the top of bed. A 3-dimensional benchmark simulation was conducted with a 750 t/day commercial incinerator using the present coupling scheme incorporating with a reduced SNCR reduction mechanism. Numerical tests were performed to investigate the effects of operating parameters such as injection position, injection speed and the normalized stoichiometric ratio (NSR) on the SNCR performance. The simulation results showed that the distributions of gas velocity, temperature and NOx concentration were highly non-uniform, which made the injection position one of the most sensitive operating parameters influencing the SNCR performance of moving grate incinerators. The simulation results also showed that multi-layer injections were needed to meet the EU2000 standard, and a NSR 1.5 was suggested as a compromise of a satisfactory NOx reduction and reasonable NH3 slip rates. This work provided useful guides to the design and operation of SNCR process in moving-grate incinerators.  相似文献   
358.
Despite long-standing knowledge of the benefits of riparian buffers for mitigating nonpoint source pollution, many streams are unprotected by buffers. Even landowners who understand ecological values of buffers mow riparian vegetation to the streambank. Do trends in rural riparian conditions reflect the development of riparian forest science? What motivates residential riparian management actions? Using high-resolution orthoimagery, we quantified riparian conditions and trends between 1998 and 2015 in the rural upper Little Tennessee River basin in Macon County, North Carolina and explored how landowners view riparian zone management and riparian restoration programs. Buffer composition in 2015 was as follows: no buffer (32.5%), narrow (19.3%), forested (26.7%), shrub (7.2%), and intermediate (7.0%). Relative to 1998, the greatest decrease occurred in the no buffer class (−17.7%, 46 km) and the largest increases occurred in the shrub (+72.5%, 20 km) and narrow (12.6%, 14 km) classes. Forested buffer marginally increased. Semi-structured interview data suggest that landowners prioritize recreational and scenic aspects of riparian buffers over ecological functions such as filtration and bank stabilization. Riparian restoration programs might be made more enticing to non-adopters if outreach language appealed to landowner priorities, design elements demonstrated intentional management, and program managers highlighted areas where ecological goals and landowner values align.  相似文献   
359.
A simple and cost-effective analysis method based on quartz crystal nanobalance (QCN) coated with a molecularly imprinted polymer (MIP) for measurement of methomyl was investigated. In the first part of this study, a sensitive, selective and reliable quartz crystal nanobalance (QCN) sensor was designed for the selective determination of methomyl in aqueous solutions. In the second part, in order to demonstrate the applicability and performance of the fabricated sensor in the real world situation, it was successfully applied for the determination of methomyl residual in photo catalytic degradation by ZnO powders in aqueous solutions. The fabricated sensor presents a high selectivity and sensitivity (4.56 Hz per mg L?1) for methomyl and it can be used for determination of methomyl concentration ranged between 1 to 45 mg L?1. Furthermore, good reproducibility, R.S.D. = 2.14% (n = 5) was observed. To investigate the performance of the sensor, the change in the insecticide concentration during the photocatalytic degradation of methomyl by ZnO was investigated by QCN and UV/Vis spectroscopy. Results obtained from QCN sensor and UV/Vis spectroscopy measurement are in good mutual agreement. So the fabricated sensor may provide an efficient, low cost, easy-to-use method for the in-field evaluation of specific targeted analytes in aqueous solutions which in turn may lead to improved food and water safety.  相似文献   
360.
Abstract: The links between species–environment relations and species’ responses to protection are unclear, but the objectives of marine protected areas (MPAs) are most likely to be achieved when those relations are known and inform MPA design. The components of a species’ habitat vary with the spatial resolution of the area considered. We characterized areas at two resolutions: 250 m2 (transect) and approximately 30,000 m2 (seascape). We considered three categories of environmental variables: substrate type, bottom complexity, and depth. We sought to determine at which resolution habitat characteristics were a better predictor of abundance and species composition of fishes and whether the relations with environmental variables at either resolution affected species’ responses to protection. Habitat features accounted for a larger proportion of spatial variation in species composition and abundances than differences in protection status. This spatial variation was explained best by habitat characteristics at the seascape level than at the transect level. Species’ responses to protected areas were specific to particular seascape characteristics, primarily depth, and bottom complexity. Our method may be useful for prioritizing marine areas for protection, designing MPAs, and monitoring their effectiveness. It identified areas that provided natural shelter, areas acting as buffer zones, and areas where fish species were most responsive to protection. The identification of such areas is necessary for cost‐effective establishment and monitoring of MPAs.  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