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   90701篇
  免费   1275篇
  国内免费   1351篇
安全科学   3821篇
废物处理   3288篇
环保管理   14010篇
综合类   21546篇
基础理论   26316篇
环境理论   74篇
污染及防治   14652篇
评价与监测   5379篇
社会与环境   3674篇
灾害及防治   567篇
  2022年   838篇
  2021年   841篇
  2020年   716篇
  2019年   877篇
  2018年   1141篇
  2017年   1177篇
  2016年   2199篇
  2015年   1860篇
  2014年   2612篇
  2013年   9310篇
  2012年   2270篇
  2011年   2590篇
  2010年   3326篇
  2009年   3465篇
  2008年   2064篇
  2007年   1913篇
  2006年   2280篇
  2005年   2246篇
  2004年   2566篇
  2003年   2384篇
  2002年   1931篇
  2001年   2187篇
  2000年   1971篇
  1999年   1497篇
  1998年   1366篇
  1997年   1361篇
  1996年   1476篇
  1995年   1577篇
  1994年   1461篇
  1993年   1320篇
  1992年   1303篇
  1991年   1276篇
  1990年   1233篇
  1989年   1188篇
  1988年   1037篇
  1987年   972篇
  1986年   985篇
  1985年   1066篇
  1984年   1161篇
  1983年   1161篇
  1982年   1174篇
  1981年   1096篇
  1980年   942篇
  1979年   926篇
  1978年   817篇
  1977年   716篇
  1976年   637篇
  1975年   603篇
  1973年   632篇
  1972年   636篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
The towed undulating vehicle (TUV), named SARAGO, was used for two fine-scale surveys between the Italian and the Sardinian coasts during the Astraea 2 cruise (6-7 and 26-27 September 1995), studying the deep chlorophyll maximum distribution. SARAGO sections identify a sub-surface doming with higher chlorophyll a and primary production concentrations in the upwelling area of a cyclonic gyre region, detected by sea-surface temperature images. In the first section, the cyclone presents a double doming, in density and salinity, with shallower and concentrated patches of chlorophyll a for about 2 miles. Twenty days later, the second section shows that the gyre changes shape and extension, showing a single doming with higher primary production and chlorophyll a concentrations, distributed over a large area of about 40 nautical miles. SARAGO allows analysis of this high-variability phenomenon (cyclonic gyre) and allows concentrated patches (2 nm) to be identified, thus proving the importance of TUVs in the study of mesoscale processes.  相似文献   
83.
84.
85.
86.
Protected areas in developing countries play a vital role in promoting the ideal of sustainable development.But 'people-park'conflicts are commonplace,threatening the future of these areas and the long term well-being of local communities. Surprisingly, little attention has been given to applying lessons learned in conflict studies to people-parkconflicts. In contrast to traditional adversarialresponses, negotiated approaches offer considerable potential for transforming people-park conflicts into mutually beneficial relationships.Experiencesin the Richtersveldregion of South Africa demonstrate the cardinal role negotiation can play in addressing key issues underlying people-park conflicts.  相似文献   
87.
Risk homeostasis theory postulates that people accept a specific level (target level) of risk in a given activity in return for benefits accruing from that activity. It follows that, if people expect a great deal from the future, the less likely they are to jeopardise it by taking risks in respect of their health and safety. One effective method for reducing target level of risk are incentives, and the available literature contains ample evidence of the effectiveness of incentives programmes in accident prevention. As incentives essentially imply an enhanced quality of life in the future, the question arises as to how expectations of the future may be related to health and safety habits. In order to explore the relationship between perceived value of the future and health and safety habits, an analysis of the psychological literature on individual differences in future time orientation/perspective is presented. Four factors are identified: (1) clear ideation of the future, (2) active planning for the future, (3) time pressure, and (4) optimistic expectations about events outside one's own control. It is hypothesised that factors (1) and (2) are associated with positive health and safety habits, while factors (3) and (4) may characterise individuals with relatively high target levels of physical risk. Research questions and procedures for the study of these relationships are discussed.  相似文献   
88.
89.
H. Sudo  M. Azeta 《Marine Biology》1992,113(2):211-217
Ontogenetic change of habitat depths of Nautilus pompilius in the Philippines (Tañon Strait) and Fiji is considered by comparing 18O/16O ratios in septa and cameral fluid of live-caught specimens and ambient sea-water. 18O values of cameral liquid become heavier with decreasing volume within a chamber, which may be due to isotopic fractionation during discharge across the siphuncular wall. All of the seven Philippine and Fiji specimens analyzed show a distinct change in 18O from light values in the first seven septa to heavier values in the succeeding septa. Two different isotopic temperature scales are obtained for the Fiji and Philippine populations, suggesting a differential vital effect of metabolism between them. Sightly light 18O values in Septa 1 to 7 and hatching at relatively high temperatures in aquaria both suggest that N. pompilius hatch at the shallowest depths within their inhabitable vertical range. Depths of postembryonic animals in the Philippines and Fiji waters estimated from the isotopic temperature-depth diagrams range from 120 to 160 m and from 440 to 520 m, respectively, both of which correlate well with capture records. More than several tens of small-scale 18O cycles are detected in the sequence of nacreous layers within the single septum of a submature Philippine specimen. This can be interpreted as reflecting daily vertical migration.  相似文献   
90.
Laboratory experiments conducted during 1987 on Appledore Island, Maine, USA, tested whether feeding preference or the absence of an attractant was the cause for the occurrence of beds of Codium fragile ssp. tomentosoides (herein referred to as Codium fragile) within rocky barrens grazed clear of kelp by the sea urchin Strongylocentrotus droebachiensis. Consumption of C. fragile in single-diet experiments (1 seaweed/sea urchin) was highly variable and was not significantly different from that for several other seaweeds (Agarum cribrosum, Ascophyllum nodosum, Chondrus crispus, and Laminana saccharina) important in the field diet of the green sea urchin. In multiple-diet experiments (5 seaweeds/sea urchin) significantly less Codium fragile was eaten than Chondrus crispus, but significantly more Codium fragile was eaten than A. cribrosum. Chemosensory experiments suggest that C. fragile does not attract the sea urchin. Sea urchins are unable to detect C. fragile but will eat it when they come in contact with it.  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