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   32888篇
  免费   347篇
  国内免费   245篇
安全科学   868篇
废物处理   1206篇
环保管理   4153篇
综合类   6268篇
基础理论   9102篇
环境理论   26篇
污染及防治   8369篇
评价与监测   1934篇
社会与环境   1348篇
灾害及防治   206篇
  2022年   221篇
  2021年   213篇
  2019年   243篇
  2018年   441篇
  2017年   426篇
  2016年   623篇
  2015年   537篇
  2014年   758篇
  2013年   2291篇
  2012年   943篇
  2011年   1317篇
  2010年   1122篇
  2009年   1131篇
  2008年   1355篇
  2007年   1453篇
  2006年   1276篇
  2005年   1085篇
  2004年   1074篇
  2003年   1034篇
  2002年   1000篇
  2001年   1293篇
  2000年   915篇
  1999年   609篇
  1998年   461篇
  1997年   476篇
  1996年   466篇
  1995年   518篇
  1994年   478篇
  1993年   421篇
  1992年   439篇
  1991年   404篇
  1990年   407篇
  1989年   438篇
  1988年   368篇
  1987年   316篇
  1986年   295篇
  1985年   330篇
  1984年   302篇
  1983年   332篇
  1982年   338篇
  1981年   287篇
  1980年   266篇
  1979年   298篇
  1978年   251篇
  1977年   219篇
  1976年   221篇
  1975年   209篇
  1974年   185篇
  1973年   197篇
  1972年   216篇
排序方式: 共有10000条查询结果,搜索用时 408 毫秒
11.
12.
Journal of Material Cycles and Waste Management - The traditional Chinese medicinal plant Magnolia officinalis has a wide range of applications; including more than 200 kinds of patented Chinese...  相似文献   
13.
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   
14.
15.
16.
17.
The genetic polymorphism of natural populations of Lepilemur mustelinus ruficaudatus was studied by protein electrophoresis. We sampled blood from 72 individuals from four populations separated by geographic or anthropogenic barriers from southwestern Madagascar. Six out of 22 enzyme loci showed genetic variation with a degree of polymorphism of 0.273. The expected and observed degree of genetic heterozygosity over all loci is similar to that of other primates (He = 0.058, Ho = 0.036). The F-statistics revealed that the four subpopulations were similar with respect to gene structure (FST = 0.065, p = 0.016), but the genotypic structures within subpopulations were inconsistent with random mating. For the total of the four subpopulations the proportion of heterozygous individuals was significantly smaller than expected under random mating (FIS = 0.373, FIT = 0.414, p < 0.01). These results correspond closely to what is expected considering the low migration ability of individuals of L. m ruficaudatus leading to small and rather isolated inbred populations.  相似文献   
18.
19.
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   
20.
The periodicity of fires in larch forests of Evenkia and their relationship with landscape elements have been studied. Cross-sections with “burns” in them caused by past fires have been analyzed in 72 test plots; the fire chronology encompassed the period from the 15th to the 20th century. The between-fire intervals (BFIs) have been calculated by two methods: (I) on the basis of burns alone and (II) on the basis of burns and the start of growth of the new generation of larch after the earliest fire. The BFI depends on local orographic features; it is 86 ± 11 (105 ± 12), 61 ± 8 (73 ± 8), 139 ± 17 (138 ± 18), and 68 ± 14 (70 ± 13) years for northeastern slopes, southwestern slopes, bogs, and flatlands, respectively. The mean BFIs calculated by methods I and II are 82 ± 7 and 95 ± 7 years, respectively. The permafrost horizon rises at a mean rate of 0.3 cm per year after a forest fire. It has been shown that the number of fires regularly peaks at periods of 36 and 82 years. There is also a temporal trend in fire frequency: the mean BFI was approximately 100 years in the 19th century and 65 years in the 20th century.  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