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   39095篇
  免费   422篇
  国内免费   316篇
安全科学   1288篇
废物处理   1779篇
环保管理   5368篇
综合类   6126篇
基础理论   10299篇
环境理论   15篇
污染及防治   9558篇
评价与监测   2668篇
社会与环境   2472篇
灾害及防治   260篇
  2022年   346篇
  2021年   389篇
  2020年   256篇
  2019年   319篇
  2018年   580篇
  2017年   571篇
  2016年   900篇
  2015年   688篇
  2014年   1056篇
  2013年   3173篇
  2012年   1275篇
  2011年   1724篇
  2010年   1412篇
  2009年   1537篇
  2008年   1765篇
  2007年   1720篇
  2006年   1557篇
  2005年   1382篇
  2004年   1299篇
  2003年   1268篇
  2002年   1201篇
  2001年   1446篇
  2000年   1025篇
  1999年   648篇
  1998年   463篇
  1997年   507篇
  1996年   527篇
  1995年   621篇
  1994年   539篇
  1993年   480篇
  1992年   477篇
  1991年   484篇
  1990年   466篇
  1989年   445篇
  1988年   384篇
  1987年   335篇
  1986年   352篇
  1985年   326篇
  1984年   370篇
  1983年   351篇
  1982年   367篇
  1981年   311篇
  1980年   246篇
  1979年   279篇
  1978年   221篇
  1977年   206篇
  1975年   198篇
  1974年   183篇
  1973年   225篇
  1972年   193篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Introduced and cryptogenic species in Port Phillip Bay, Victoria, Australia   总被引:4,自引:0,他引:4  
Port Phillip Bay (PPB) is a large (1,930 km2), temperate embayment in southern Victoria, Australia. Extensive bay-wide surveys of PPB have occurred since 1840. In 1995/1996 the Commonwealth Scientific and Industrial Research Organization (CSIRO) Centre for Research on Introduced Marine Pests (CRIMP) undertook an intensive evaluation of the region with the aims of developing a comprehensive species list of native and introduced biota and contrasting previous bay-wide assessments with a current field survey in order to detect new incursions and discern alterations to native communities. Two methods were used to meet these aims: a re-evaluation of regional museum collections and published research in PPB to identify and determine the timing of introductions; and field surveys for benthic (infauna, epifauna and encrusting) organisms between September 1995 to March 1996. One hundred and sixty introduced (99) and cryptogenic (61) species were identified representing over 13% of the recorded species of PPB. As expected, the majority of these are concentrated around the shipping ports of Geelong and Melbourne. Invasions within PPB appear to be increasing, possibly due to an increase in modern shipping traffic and an increase in aquaculture (historically associated with incidental introductions); however the records of extensive biological surveys suggest that this may, in part, be an artefact of sampling effort. In contrast to Northern Hemisphere studies, PPB (and Southern Hemisphere introductions in general) have significantly different suites of successfully invading taxa. PPB is presented as one of the most invaded marine ecosystems in the Southern Hemisphere.Communicated by M.S. Johnson, Crawley  相似文献   
22.
23.
24.
25.
ABSTRACT: The use of nonparametric tests for monotonic trend has flourished in recent years to support routine water quality data analyses. The validity of an assumption of independent, identically distributed error terms is an important concern in selecting the appropriate nonparametric test, as is the presence of missing values. Decision rules are needed for choosing between alternative tests and for deciding whether and how to pre-process data before trend testing. Several data pre-processing procedures in conjunction with the Mann-Kendall tau and the Seasonal Kendall test (with and without serial correlation correction) are evaluated using synthetic time series with generated serial correlation and missing data. A composite test (pre-testing for serial correlation followed by one of two trend tests) is evaluated and was found to perform satisfactorily.  相似文献   
26.
27.
Pentachlorotoluene (PCT) and pentabromotoluene (PBT) are environmental contaminants detected in the Great Lakes ecosystem. In view of the paucity of toxicity data and the potential for human exposure, a subacute (28 day) and a subchronic (91 day) study were conducted in the rat. In the subacute study, groups of 10 male and 10 female rats were fed the diet containing PCT or PBT at 0, 0.5, 5.0, 50 or 500 ppm for 28-days. In the subchronic study, the group size was increased to 15, the dose levels were 0, 0.05, 0.5, 5.0, 50 and 500 ppm in the diet and the exposure period was 91 days. Growth rate and food consumption were not affected by exposure to either chemical in the subacute and subchronic study. Clinical observations revealed no abnormalities. Decreased hemoglobin was observed in female rats fed 5.0 ppm PCT and higher levels in the subacute (28 day) study. In the same study the hematocrit value and erythrocyte numbers of females fed 5.0 or 500 ppm PCT diets were significantly lower than the control. In both subacute and subchronic studies mild dose-dependent histopathological changes were observed in the thyroid, liver and kidney of rats fed PCT and PBT diets. In general male rats were more susceptible than females to the treatment of PCT and PBT. Based on these data, it was concluded that the no observable adverse effect level for PCT was 50 ppm in the diet (3.5 mg/kg b.w./day) and that of PBT was 5.0 ppm (0.35 mg/kg b.w./day).  相似文献   
28.
29.
30.
While the world is going into different tourism expectations, the tourism understanding in Turkey is defined as tourism in the sea-sand-sun triangle. However, it is possible to contribute to the income and local development of the indigenous people by developing nature-based tourism. Besides, with the sustainable use and preservation of the natural-cultural assets, the damage of the traditional tourism industry on the natural and cultural environment could be reduced. In this study, it is aimed to bring up the nature-based tourism concept in Çanakkale by evaluating the nature-based tourism industry in the general of Turkey and assessing the natural-cultural resources that Çanakkale comprehends. The most important areas that have a nature-based tourism potential in Çanakkale and the tourism activities that are most suitable for these areas have been determined.  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