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   16624篇
  免费   158篇
  国内免费   98篇
安全科学   450篇
废物处理   627篇
环保管理   2339篇
综合类   2706篇
基础理论   4494篇
环境理论   4篇
污染及防治   4298篇
评价与监测   1007篇
社会与环境   851篇
灾害及防治   104篇
  2022年   115篇
  2021年   134篇
  2020年   124篇
  2019年   179篇
  2018年   224篇
  2017年   224篇
  2016年   357篇
  2015年   252篇
  2014年   366篇
  2013年   1271篇
  2012年   451篇
  2011年   640篇
  2010年   538篇
  2009年   523篇
  2008年   692篇
  2007年   694篇
  2006年   664篇
  2005年   507篇
  2004年   592篇
  2003年   523篇
  2002年   486篇
  2001年   707篇
  2000年   471篇
  1999年   286篇
  1998年   244篇
  1997年   218篇
  1996年   232篇
  1995年   250篇
  1994年   274篇
  1993年   220篇
  1992年   250篇
  1991年   224篇
  1990年   258篇
  1989年   238篇
  1988年   193篇
  1987年   174篇
  1986年   158篇
  1985年   167篇
  1984年   192篇
  1983年   180篇
  1982年   185篇
  1981年   179篇
  1980年   137篇
  1979年   153篇
  1978年   131篇
  1977年   117篇
  1975年   118篇
  1974年   115篇
  1973年   110篇
  1972年   133篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
821.
The influence of the water-accommodated fraction of No. 2 fuel oil on aspects of larval development of Cancer irroratus (Say) has been investigated. Rates of survival, respiration, ingestion and growth were estimated for both oil-treated and untreated larvae. Larvae reared in oil-treated water exhibited lower survival to megalopa than did larvae reared in untreated water. The presence of oil also altered several aspects of larval energetics. Reductions were seen in food consumption and growth rate while the metabolic cost of maintenance increased. One overall effect that may occur as a result of lowered larval survival and growth rate would be the reduction in larval recruitment in oil-polluted areas.  相似文献   
822.
823.
A study of marine boring and fouling organisms in the vicinity of the thermal effluent from the Oyster Creek Nuclear Generating Station, Barnegat Bay, New Jersey, USA has been conducted since 1971. Two subtropical species of shipworms have been found in significant numbers in the effluent. These are Teredo bartschi Clapp and Teredo furcifera von Martens. The shipworm Lyrodus sp. and the flatworm Taenioplana teredini Hyman, which is predatory on teredinids, were also found, but on only one occasion. The polychaete Ficopomatus enigmaticus (Fauvel) has been found for the first time on the Atlantic Coast of North America. Three other polychaetes, Potamilla (Potamethus) spathiferus (Ehlers), Loimia medusa (Savigny), and Sphaerosyllis sp., have been newly identified from Barnegat Bay, but probably are not recent range extensions. Only T. bartschi, T. furcifera, and F. enigmaticus have established breeding populations. Their distributions and abundances are probably related to the thermal effluent; this is most clear in the case of T. bartschi and least clear in the case of F. enigmaticus. T. bartschi was confined at first to the heated effluent in Oyster Creek, but has spread to Forked River. It has become a major faunal element in Oyster Creek. The impact of the other exotic species has been negligible. The primary mechanism of the range extensions is by boat transport.  相似文献   
824.
The turnover rate constants (k) of alanine in coastal marine sediments were measured using 3H-and 14C-alanine in tracer amounts (less than in situ concentrations of alanine in the porewater). After incubation 14C-label was recovered in free dissolved alanine, adsorbed alanine, volatile fatty acids and carbon dioxide pools. Alanine left the free dissolved pool by two processes: 1) adsorption (k=0.06 min-1) and 2) biological uptake (k=0.16 min-1). Adsorption of alanine was deduced from the persistence of 14C-alanine, which was slowly metabolized after an initial rapid rate of degradation. Adsorption was confirmed in biologically inactivated sediments. The adsorbed 14C-alanine was only partially exchanged by the addition of excess non-labelled alanine, indicating the existence of at least 2 different adsorbed pools. The rates of adsorption and desorption were equal, but the k-values were different, indicating that the adsorbed pool was 2500 fold greater than the free pool. From the biological turnover rate constant (0.16 min-1), the mineralization percentage (80%) and the concentration of alanine (800 nmol l-1 of porewater) a mineralization rate in the sediment of 75 nmol cm-3 d-1 was determined. This was in excess of the measured total NH 4 + production. It is concluded that much of the dissolved alanine (800 nm) was biologically unavailable and a more realistic free dissolved pool would be 10 nM.  相似文献   
825.
The major objective of the investigation was to evaluate the road traffic noise and its likely impacts on the local community of Asansol city (West Bengal, India) by monitoring and modeling. The attitudinal response of local population due to existing vehicular noise is presented in the paper. Noise and Attitudinal Survey was conducted at 25 locations. A total of 869 individuals were surveyed. The relationship between traffic noise levels and annoyance was studied using correlation, linear and multiple linear regressions analysis. The average L(dn) value was 73.28 +/- 8.51 dB(A) (55.1-87.3); The Traffic Noise Index (TNI) was 80.62 +/- 15.88 dB(A) (49.4-115.8). The mean value of percent of population Highly Annoyed (%HA) due to road traffic noise was 26.50 +/- 3.37 (19.44-33.2), whereas the mean dissatisfaction score (MDS) was 2.96 +/- 0.90 (1.04-4.45). Annoyance modeling was also performed based on field data. It can be said that Noise values gives desirable annoyance predicting values in comparison to vehicular data.  相似文献   
826.
In present study horizontal and vertical distribution of traffic-related pollutants (CO and SO(2)) within the street canyons in (CO and SO(2)) Varanasi, India was monitored. The results showed that average horizontal profiles of traffic-related pollutant concentrations within street canyon at leeward side were approximately same as that of windward side. However, the vertical concentration of both the pollutants decreases with height above the ground and study indicated that CO and SO(2) concentrations at different heights below the roof showed clear vertical self-gradient. CO and SO(2) concentration decreased with height and the minimum value occurred at the roof. It was concluded from the observed results that pollutants from vehicular exhaust emissions in the street canyon of Varanasi were evenly distributed. This result may be due to the fact that wind vortices are not formed. Therefore, urban planners can use this type of streets so that there is proper ventilation and dispersal of pollutants.  相似文献   
827.
A conditional time-averaged gradient (COTAG) system has been developed to provide direct long-term (weekly to monthly) average flux gradient measurements for a range of trace gases, between land and atmosphere. Over daily periods, atmospheric conditions can range from high stability, where the vertical gradients of ambient concentration are enhanced due to very small diffusivity, to highly unstable conditions, in which concentration gradients are small due to the intense turbulent activity of the surface layer. The large vertical gradients generated by high stability would bias the estimate of the actual flux: to avoid this, the COTAG system samples conditionally, within a carefully refined range of stability. A comparison with a continuous flux gradient system suggested that the removal of stable conditions from the sampling period does not substantially modify the evaluation of the long-term fluxes.  相似文献   
828.
The purpose of this study was to characterize the polycyclic aromatic hydrocarbon (PAH) contamination in the sediments of stormwater detention ponds in coastal South Carolina. Levels of the sum of PAH analytes were significantly higher in the sediments of commercial ponds compared to that of reference, golf course, low-density residential, and high-density residential ponds. Isomer ratio analysis suggested that the predominant source of PAHs were pyrogenic; however, many ponds had a PAH signature consistent with mixed uncombusted and combusted PAH sources. PAH levels in these sediments could be modeled using both pond drainage area and pond surface area. These results demonstrate that the sediment from most commercial ponds, and a few residential and golf course ponds, were moderately contaminated with PAHs. PAH levels in these contaminated ponds exceeded between 42% and 75% of the ecological screening values for individual PAH analytes established by US EPA Region IV, suggesting that they may pose a toxicological risk to wildlife.  相似文献   
829.
With the aim of giving an overview on concentration and distribution of Cd, Cu, and Pb in fish from the coasts of Sinaloa state (SE Gulf of California), specimens with different feeding habits were collected in five locations. Sampling occurred between June 2003 and March 2004. Metal analyses on fish tissues were made by graphite furnace (Cd, Pb) and flame (Cu) atomic absorption spectrophotometry. Metal concentrations in tissues of carnivorous fish were grouped together and compared with corresponding concentrations in non-carnivorous fish; Cu and Pb levels were significantly (p?<?0.05) higher in liver of non-carnivorous species. Though no samples exceeded the maximum level set in international legislation for fish, from the perspective of the public health and considering the legal limits of fishery products for human consumption, Cu concentrations were exceeded (in tissues different from muscle) in four carnivorous and five non-carnivorous species according to the Australian legislation. In the case of Cd, two carnivorous species (Pomadasys leuciscus and Caulolatilus princeps) and one non-carnivorous species (Mugil cephalus), showed concentrations over the maximum level of 2 μg g???1 dry weight considered in the Mexican legislation. Considering average amounts of fish consumption in Mexico, daily mineral intake (DMI) values for Cu and percentage weekly intake (PWI) of Cd and Pb were estimated; none of the analyzed metals in edible portion of analyzed fish could be detrimental to humans.  相似文献   
830.
The distribution and accumulation of heavy metals in the sediments, especially those nearest of wastewater discharges of south of Spain, were investigated. Sediment samples from 14 locations were collected and characterised for metal content (e.g. Ni, Cu, Zn, Cr, Pb, Mn, Cd and Hg), organic carbon, total nitrogen, total phosphorous, n-hexane-extractable material, carbonates and grain size. Concentration data were processed using correlation analysis and factor analysis. The correlation analysis of concentrations data showed important positive correlations among organic carbon, total phosphorus, Cu, Zn, Cd and Hg, otherwise weak correlations among Mn, Cr, Ni and CO3 2???, indicating that these metals have complicated geochemical behaviours. The use of statistical factor analysis also confirmed these results. Sediments pollution assessment was carried out using geoaccumulation and metal pollution indexes (MPI8). The results revealed that sediments of Cádiz bay and Sancti Petri channel were uncontaminated with the studied metals.  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