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   111篇
  免费   0篇
  国内免费   3篇
安全科学   14篇
废物处理   1篇
环保管理   24篇
综合类   14篇
基础理论   23篇
环境理论   1篇
污染及防治   19篇
评价与监测   14篇
社会与环境   2篇
灾害及防治   2篇
  2022年   2篇
  2020年   1篇
  2019年   2篇
  2018年   2篇
  2017年   2篇
  2016年   2篇
  2015年   2篇
  2014年   1篇
  2013年   2篇
  2012年   3篇
  2011年   4篇
  2010年   7篇
  2009年   8篇
  2008年   3篇
  2007年   7篇
  2006年   5篇
  2005年   5篇
  2004年   7篇
  2003年   6篇
  2002年   4篇
  2001年   3篇
  2000年   4篇
  1999年   2篇
  1998年   1篇
  1997年   1篇
  1996年   1篇
  1995年   3篇
  1993年   2篇
  1992年   2篇
  1991年   3篇
  1990年   2篇
  1989年   2篇
  1986年   2篇
  1984年   1篇
  1982年   3篇
  1980年   1篇
  1979年   1篇
  1975年   3篇
  1973年   1篇
  1971年   1篇
排序方式: 共有114条查询结果,搜索用时 15 毫秒
21.
Cryptocurrencies have the potential to revolutionize the exchange of information and money through blockchain and distributed ledger technologies. Despite the promise of such underlying technologies, their reliance upon distributed consensus processes to approve software updates raises the potential for governance failures to destabilize a given cryptocurrency. These governance failures, known as ‘hard forks,’ can separate a cryptocurrency into two rival camps. Where such events can destabilize a given cryptocurrency’s value, and instill distrust in the capacity of a cryptocurrency to survive as a reliable vehicle of exchange, it is imperative for the cryptocurrency community to improve their governance processes and limit the potential for hard forks to occur. While the distributed nature of cryptocurrency governance makes any traditional governing process unlikely to succeed, anticipatory approaches that establish thresholds and metrics to determine when software reform is necessary may help alleviate the governance failures presented by many hard forks.  相似文献   
22.
Here we assessed retinoids as biomarkers of contaminant exposure by studying whether the sex, age, lipid content and organochlorine concentrations of bottlenose dolphins induced variation in retinoid status and its deposition in blubber. Blubber samples were collected from 47 individuals of known age and gender from Sarasota Bay in June 2000 and 2001. The sample included a representative cross-section of the resident dolphin community, with ages ranging from 2 to 50 years. Organochlorine levels showed the age- and sex-related variation commonly observed in other species, with concentrations increasing in youngsters of both sexes and in adult males, and decreasing in adult females after the onset of maturity. Blubber lipid content was low in the overall population and significantly decreased with age in adult males. Retinoid blubber concentrations were comparable to other odontocete species previously studied, and were strongly determined by lipid content. As a consequence of the latter, retinoid concentration was observed to decrease with age in adult males. This effect could not be statistically dissociated from the negative correlation observed between levels of organochlorines and retinoid blubber concentration. Consequently, we could not clarify whether high organochlorine loads in this population lowered retinoid concentrations or, conversely, whether depleted lipid reserves were indeed responsible for the high organochlorine concentrations and the low retinoid levels detected in blubber. With the current knowledge, both options should be considered and investigated, with initial focus on male dolphins.  相似文献   
23.
Summary The vocal behavior of Hyla versicolor was studied in the field by means of behavioral observations and playback experiments, and these data were coupled with measurements of oxygen consumption in calling frogs to estimate the effect of social interactions on calling energetics. Male gray treefrogs have intense calls (median peak SPL=109 dB, fast RMS SPL=100 dB at 50 cm). At an air temperature of 23° C, males produced an average of 1,200–1,300 calls/h for 2–4 h per night. Calling rates and call durations differed among individuals, but were relatively constant for each male during periods of sustained calling. Males in dense choruses gave calls about twice as long as isolated males, but produced calls at about half the rate. Consequently, total calling effort and estimated aerobic costs were largely independent of chorus density. Playbacks of recorded calls to males in the field elicited increases in call duration and decreases in calling rate, regardless of the rate or duration of the stimulus. Males gave longer calls in response to long calls or to stimuli presented at high rates, but they did not precisely match either stimulus rate or duration. Calling effort and estimated oxygen consumption changed only slightly during stimulus playbacks. These results indicate that male-male competition elicits pro-found changes in the vocal behavior of calling males, but these changes have little effect on energy expenditure. We estimated that most calling males had metabolic rates of about 1.7–1.8 ml O2/(g\h), or about 280 J/h for an average size (8.6 g) male at 20° C. Although changes in call duration and calling rate did not affect aerobic costs of calling, males producing long calls at slow rates called for fewer hours per night than males producing shorter calls at higher rates. This suggests that calling time may be limited by the rate at which muscle glycogen reserves are depleted.  相似文献   
24.
Signature whistles of 42 free-ranging bottle-nose dophin calves were compared to those of their mothers. Humans judged their similarity by inspection of spectrograms. There was a sex difference in the tendency of calves to produce whistles similar to or different from those of their mothers; most female calves produced whistles that were different from those of their mothers, whereas male calves were more likely to produce whistles that were similar to those of their mothers. Because matrilineally related females associate together and use signature whistles to establish and/or maintain contact with their calves, there may be a selective pressure for females to produce whistles that are distinct from those of their mothers. There may be fewer constraints governing whistle development in males, with the result that some males produce whistles similar to those of their mothers and others do not.  相似文献   
25.
The toxicity of seawater dispersions of a chemical dispersant to two marine crustaceans was investigated in the presence and absence of various quantities of a non-toxic mineral oil. From the results and a physical-chemical partitioning analysis, a limiting value of the oil-water partition coefficient of the toxic compounds is deduced suggesting that essentially all of the toxic compounds in the dispersant will partition into solution in water following dispersant application to an oil spill. This conclusion simplifies interpretation and prediction of the toxic effects of a dispersed oil spill.The combined bioassay-partitioning procedure may have applications to the study of the toxicity of other complex mixtures such as industrial effluents.  相似文献   
26.
de Boer J  Oehme M  Smith K  Wells DE 《Chemosphere》2000,41(4):493-497
Two interlaboratory studies on individual toxaphene congeners have been organised by the project Quality Assurance of Information for Marine Environmental Monitoring in Europe (QUASIMEME). Fifteen laboratories analysed two standard solutions in the first study and 13 laboratories analysed a standard solution and two cleaned biota extracts in the second study. The coefficients of variation obtained for the standard solutions were 6-21% and for the cleaned extracts 16-39%. Although the results were comparable to those of other studies, further improvement in the level of agreement between the participating laboratories was considered possible.  相似文献   
27.
During July of 1983, 1986, and 1987, we measured rates of oxygen consumption of 234 individuals of 17 species of midwater crustaceans (orders Decapoda, Mysidacea, and Euphausiacea) off the Hawaiian islands at depths from the surface to greater than 1200 m. The routine metabolic rates declined with increasing depths of the species' occurrence to an extent greater than could be accounted for by depth-related changes in body size or water temperature. Most species appeared able to regulate their oxygen consumption down to the lowest oxygen partial pressures found in their depth range (20 mm Hg O2), but did not regulate to such low oxygen partial pressures as did similar midwater crustaceans off California, where oxygen levels reach as low as 6 mm Hg. Metabolic rates of the shallower-living, but not the deepest-living Hawaiian crustaceans were significantly higher than those of Californian crustaceans. This is interpreted as indicating that the metabolic rates of midwater crustaceans are not adapted specifically to differing levels of primary production and that the decline with depth of metabolic rates in these species is not the result of food limitation at depth. The data are, however, consistent with the hypothesis that lower metabolic rates at depth are due to the relaxation of selection pressures relating to visual predation near the surface.  相似文献   
28.
We characterized the prey field and the lipid classes/fatty acids in the flesh of age 0 juvenile cod (Gadus morhua) during their late-summer/fall arrival and settlement into eelgrass (Zostera marina) in coastal Newfoundland. Examination of available prey demonstrated a high abundance of small zooplankton (Acartia, Microsetella and Oithona sp.) with no larger Calanus sp. prey. Breakpoint analysis showed significant changes in the accumulation of relative (mg g−1 wet weight) and absolute (μg fish−1) amounts of lipid with standard length at the time of settlement (~60 mm standard length). Settling juvenile cod showed an alternate lipid utilization strategy where they catabolized phospholipids (PL) to a greater extent than triacylgylcerols (TAG). Polyunsaturated fatty acids (PUFA) content in cod flesh decreased as fish grew indicating that nearshore zooplankton quality was not optimal for PL formation. The dramatic reduction in cod PL was likely due to both catabolism of muscle and a lack of dietary PUFA suitable for PL synthesis. However, juvenile cod continued to grow, leading to decreased lipid stores and suggesting that cod settling into eelgrass are under intense selection pressure for growth prior to the onset of winter, possibly as a means of escaping gape-limited predation. These data contrast better-studied freshwater and estuarine systems in which lipid storage is critical for successful overwintering.  相似文献   
29.
本文调查了可持续建筑业的社会形势,特别是发展中国家的可持续建筑业,一个有社会责任感的建筑产业,就是一个在保护劳工免受负面影响的同时努力加强正面影响作用的产业,这要求遵守劳动标准,正如“国际劳工组织(ILO)协定“和国家立法所表达的那样,志愿行动已经做出了积极的贡献,但是严格的计划将要求每一个人依照相同的游戏规则,要做到如此,全体利益相关者确定的统一行动是十分必要的,一个新的“社会责任感建设投资“行动,由国际劳工组织发起,它将把政府代表,雇主,工人和其他主要建筑利益相关者聚在一起,其目的是要制定战略和行动计划,以加强建筑作业中关键劳动标准的贯彻,以及推动建筑部门的生产性就业.  相似文献   
30.
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