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   1419篇
  免费   14篇
  国内免费   5篇
安全科学   34篇
废物处理   52篇
环保管理   150篇
综合类   698篇
基础理论   192篇
污染及防治   228篇
评价与监测   49篇
社会与环境   26篇
灾害及防治   9篇
  2017年   22篇
  2016年   10篇
  2015年   17篇
  2014年   16篇
  2013年   68篇
  2012年   40篇
  2011年   44篇
  2010年   30篇
  2009年   35篇
  2008年   38篇
  2007年   42篇
  2006年   39篇
  2005年   40篇
  2004年   46篇
  2003年   43篇
  2002年   31篇
  2001年   21篇
  2000年   17篇
  1999年   15篇
  1998年   20篇
  1995年   17篇
  1994年   11篇
  1989年   13篇
  1979年   13篇
  1978年   11篇
  1966年   10篇
  1965年   15篇
  1964年   15篇
  1963年   25篇
  1962年   17篇
  1961年   14篇
  1960年   23篇
  1959年   24篇
  1958年   15篇
  1957年   16篇
  1956年   15篇
  1955年   27篇
  1954年   33篇
  1953年   19篇
  1952年   14篇
  1951年   24篇
  1948年   9篇
  1947年   11篇
  1941年   9篇
  1939年   9篇
  1938年   12篇
  1933年   9篇
  1931年   11篇
  1930年   12篇
  1929年   13篇
排序方式: 共有1438条查询结果,搜索用时 875 毫秒
111.

Phylogenetic relationships near the origin of extant crocodylians are weakly supported, and this lack of resolution makes for poor estimates of taxonomic and morphological diversity. Previously known taxa are found throughout the Cretaceous in Laurasia and at a few sites from Brazil, Australia, and northern Africa. Here, we report Batrachomimus pastosbonensis gen. et sp. nov. from the Late Jurassic of northeastern Brazil, which is deeply nested within Neosuchia and associated to the Cretaceous Asian paralligatorids. The new taxon predates all other members of Paralligatoridae and its immediate sister group (including Eusuchia) by 30 million years. A nearly complete skull, osteoderms, and limb bones were recovered, and autapomorphies of B. pastosbonensis include a scalloped lateral margin of the rostrum in dorsal view, unsculpted alveolar margin at the caudalmost portion of the maxilla, blunt lateral prongs on the jugal at the base of the postorbital bar, hourglass shaped choanae, and pterygoid choanal septum extended between the palatal shelves of the palatines. The crocodyloid-like skull proportions and the slender, conical teeth suggest an amphibious and piscivorous life history to this 1 m long animal.

  相似文献   
112.
Abstract

To determine covariates of radon testing behavior, we surveyed by mail a random sample of all Boston University employees (N = 915) six to nine months after they had been informed of the availability of radon testing services through the University's medical center. The response rate was 58%. Analysis suggests blue collar workers were underrepresented within the response rate. Slightly more than half of the respondents (51%) were men. The majority (69%) were under the age of 45. Twenty-seven percent of the respondents (N = 143) had tested their homes for radon. Bivariate analysis revealed important differences between radon testers and nontesters. Testers were 12 times more likely to be home owners than renters (p = 0.00), and were more knowledgeable about radon's characteristics and testing procedures (p = 0.00). Testers were more likely to view radon as a serious problem (p = 0.00), to consider radon testing efficacious (p = 0.00), and to consider themselves susceptible to exposure (p = 0.00). Testers were also less likely to perceive barriers to radon testing. We used logistic regression to compare the usefulness of the Health Belief Model and the Diffusion of Innovations Model in predicting radon testing. We concluded that the knowledge deficits and barriers to radon testing identified in this study should be targeted in radon educational interventions.  相似文献   
113.
ABSTRACT: The State of Florida (1994) has adopted a plan for addressing Everglades eutrophication problems by reducing anthropogenic phosphorus loads. The plan involves implementation of Best Management Practices in agricultural watersheds and construction of regional treatment marshes (Stormwater Treatment Areas or STA's). This paper describes the development, testing, and application of a mass-balance model for sizing STA's to achieve treatment objectives. The model is calibrated and tested against peat and water-column data collected in Water Conservation Area-2A (WCA-2A), where phosphorus dynamics and eutrophication impacts have been intensively studied. The 26-year-average rate of phosphorus accretion in peat is shown to be proportional to average water-column phosphorus concentration, with a proportionality constant of 10.2 m/yr (90 percent Confidence Interval = 8.9 to 11.6 m/yr). Spatial and temporal variations in marsh water-column data suggest that drought-induced recycling of phosphorus was important during periods of low stage in WCA-2A. Maintaining wet conditions will be important to promote phosphorus removal in STA's. Sensitivity analysis of STA performance is conducted over the range of uncertainty in model parameter estimates to assess the adequacy of the model as a basis for STA design.  相似文献   
114.
ABSTRACT: Survey data collected in the San Joaquin Valley of southern California and the Grand Valley of western Colorado reveal that residents of both areas believe that a severe sustained drought is likely to occur within the next 20–25 years and that their communities would be seriously impacted by such an event. Although a severe sustained drought affecting the Colorado River Basin would cause major economic and social disruptions in these and other communities, residents express little support for water management alternatives that would require significant shifts in economic development activities or in water use and allocation patterns. In particular, residents of these areas express little support for strategies such as construction and growth moratoriums, mandatory water conservation programs, water transfers from low-to high-population areas, water marketing, or reallocations of water from agricultural to municipal/industrial uses. This rejection of water management strategies that would require a departure from “business as usual” with respect to water use and allocations severely restricts the capacity of these and similar communities to respond effectively should a severe sustained drought occur.  相似文献   
115.
Book reviews     
Baker  Ilyas  Kassas  M.  Bandler  Hans  Lisowski  Marylin  Disinger  John F.  Duthie  David  Briggs  K. B. 《The Environmentalist》1992,12(4):291-304
Environment Systems and Decisions -  相似文献   
116.
WhenPseudomonas oleovorans (GPo1) is grown on sodium octanoate under ammonium limiting conditions, it is able to accumulate a copolyester consisting of medium chain length 3-hydroxyalkanoic acids (PHAm). 3-Hydroxybutyrate is only incorporated in trace amounts. WhenP. oleovorans is equipped with the PHB biosynthetic genes ofAlcaligenes eutrophus (GPo1[pVK101::PP1]), it forms a polyester containing major amounts of 3-hydroxybutyrate. The resulting polymer however is a blend of PHAm and PHB, rather than a copolymer of 3-hydroxybutyrate and medium chain length 3-hydroxyalkanoic acids [11]. To establish whether PHAm and PHB molecules are stored in the same or separate granules by this recombinantP. oleovorans strain, we studied polymer forming cells by freeze-fracture electron microscopy. This approach is possible because previous freeze-fracture electron microscopy studies on PHAm and PHB accumulating strains have shown that PHAm and PHB granules can be distinguished from each other: PHAm granules from mushroom-like structures, whereas PHB granules from needle structures during freeze-fracturing. In this paper we show that stationary phase cells of GPo1[pVK101::PP1] contained both mushroom and needle-like structures, indicating that PHAm and PHB chains were stored in separate granules. To be able to determine whether the separation of PHAm and PHB is complete, the respective granules were separated on sucrose gradients. A total cell extract of GPo1[pVK101::PP1] which was subjected to sucrose gradient centrifugation revealed two white bands of different densities: the upper band with a density of 1.05 g/mL consisted exclusively of PHAm granules, while the lower band with a density of 1.19 g/mL consisted of PHB granules only. Thus, when bacteria synthesize both PHAm and PHB, the resulting polymer chains are segregated completely and stored in separate granules.  相似文献   
117.
Small-and large-scale farm operators and applicators urgently need user-friendly and cost-effective on-site methods to treat dilute-formulated herbicide-laden wastewater (i.e., rinsate). In this study, we investigated solvent-regenerable synthetic adsorbents, Ambersorb® 563 adsorbent, Ambersorb 572 adsorbent, and Ambersorb 575 adsorbent, as alternatives to activated carbon (Filtrasorb ® 400) for cleanup of water containing Dual 8E (a.i., metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide]) or Banvel 4L (a.i., dicamba [3,6-dichloro-2-methoxybenzoic acid]). Batch-type adsorption experiments were conducted to compare adsorptive capacities of the various adsorbents. Adsorption maxima, obtained from adsorption isotherms, indicated that of the Ambersorb adsorbents tested, Ambersorb 572 adsorbent generally exhibited the highest adsorptive capacities for the herbicides tested and was comparable to Filtrasorb 400. Solvent (methanol) regenerability studies demonstrated that herbicide was readily recovered from Ambersorb 572 adsorbent and Filtrasorb 400. In general, metolachlor was more readily recoverable than dicamba. In fixed-bed column studies, Ambersorb 572 adsorbent exhibited twice the adsorptive capacity of Filtrasorb 400. Fixed-bed columns were more effective in removing metolachlor from herbicide containing water regardless of the adsorbent used. Multicycling of Ambersorb 572 adsorbent resulted in 30% loss of adsorptive capacity for dicamba as Banvel 4L and no loss of adsorptive capacity for metolachlor as Dual 8E. Working capacity was reached after three adsorption-regeneration cycles. Fixed-bed columns packed with solvent-regenerable adsorbents may prove useful as part of an on-site wastewater disposal system.  相似文献   
118.
Prompted by the calls in recent years to link relief practice to peace-building, development, or both, several conferences and papers have recently mounted a strong critique, seeing these 'broadenings' of relief as 'eroding' or 'corrupting' core humanitarian principles and playing into neo-isolationist agendas to slash humanitarianism. This paper argues that whereas these critiques have important goals in mind when they encourage a concentration on the basics of relief, there has been a loss of subtlety in the ensuing debate. Considering each element of the debate in turn, the paper argues that there is more common ground between 'new' and 'old', 'broadened' and 'basics' relief than at first appears. In concluding, it is argued that further research on key questions, and an openness to hear all perspectives will get us further than entrenched positions and rallying cries.  相似文献   
119.
ABSTRACT

Neighborhood life expectancy varies by as much as 10 years across the City of Louisville. In 2013, the Greater Louisville Project funded by local government, businesses, and foundations, argued these differences had little to do with environmental factors. The Greater Louisville Project (2013) study argued that these neighborhood differences could be attributed 40% to socio-economic factors (with a major emphasis on education), 10% to physical environment, 30% to health behaviors, and 20% to access to medical care. To test these claims, we construct our own model of neighborhood variation in years of potential life lost (YPLL) by adding two variables testing environmental degradation. We operationalise two separate measures of environmental contamination: proximity to EPA designated brownfield sites and proximity to chemical factories in an industrial park in the neighborhood known as “Rubbertown”. We conduct several regression analyses, which show a relationship between proximity to environmental contaminants and an increase in neighborhood YPLL. Our beta weights challenge the claims made by the Greater Louisville Project, which minimize the impact nearness to environmental contaminants has on reductions in life expectancy in Louisville neighborhoods.  相似文献   
120.
It has been argued that respondents in contingent valuation (CV) surveys, asked to value complex environmental amenities, will state willingness to pay (WTP) independently of the scope of the project. Such insensitivity to scope would be at odds with rational choice, and could therefore imply that CV is not a theoretically valid method for biodiversity valuation. The scope test in the present CV study was applied to endangered species preservation. Respondents were split in four sub-samples facing different scopes of endangered species preservation. The design allowed for both external and internal scope tests. Furthermore, the tests were split according to elicitation format. Of four external tests of insensitivity to scope, one was rejected, two gave mixed results, depending on either the type of test or elicitation format, and for the last one the null hypothesis could not be rejected. Of five internal tests, insensitivity to scope was rejected in three cases, one test gave mixed results, and one could not be rejected. Survey design features of the CV study, especially an unfamiliar sub-group of endangered species, could explain the apparent insensitivity to scope observed.  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