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   17481篇
  免费   163篇
  国内免费   80篇
安全科学   472篇
废物处理   646篇
环保管理   2562篇
综合类   2822篇
基础理论   4664篇
环境理论   5篇
污染及防治   4504篇
评价与监测   1050篇
社会与环境   887篇
灾害及防治   112篇
  2022年   126篇
  2021年   150篇
  2020年   137篇
  2019年   188篇
  2018年   239篇
  2017年   240篇
  2016年   377篇
  2015年   280篇
  2014年   388篇
  2013年   1361篇
  2012年   474篇
  2011年   675篇
  2010年   567篇
  2009年   559篇
  2008年   737篇
  2007年   738篇
  2006年   702篇
  2005年   545篇
  2004年   622篇
  2003年   550篇
  2002年   513篇
  2001年   719篇
  2000年   485篇
  1999年   307篇
  1998年   259篇
  1997年   232篇
  1996年   243篇
  1995年   262篇
  1994年   285篇
  1993年   229篇
  1992年   254篇
  1991年   227篇
  1990年   265篇
  1989年   243篇
  1988年   199篇
  1987年   181篇
  1986年   160篇
  1985年   180篇
  1984年   199篇
  1983年   185篇
  1982年   191篇
  1981年   185篇
  1980年   142篇
  1979年   158篇
  1978年   133篇
  1977年   118篇
  1975年   120篇
  1974年   117篇
  1973年   111篇
  1972年   133篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
952.
This research was supported by a grant from the National Council for Research and Development, Israel, and the KFK, Karlsruhe, Germany.  相似文献   
953.
Baigger  A.  Perony  N.  Reuter  M.  Leinert  V.  Melber  M.  Grünberger  S.  Fleischmann  D.  Kerth  G. 《Die Naturwissenschaften》2013,100(9):895-898

Several social mammals, including elephants and some primates, whales and bats, live in multilevel societies that form temporary subgroups. Despite these fission–fusion dynamics, group members often maintain long-term bonds. However, it is unclear whether such individual links and the resulting stable social subunits continue to exist after a complete reorganisation of a society, e.g. following a population crash. Here, we employed a weighted network analysis on 7,109 individual roosting records collected over 4 years in a wild Bechstein’s bat colony. We show that, in response to a strong population decline, the colony’s two stable social subunits fused into a non-modular social network. Nevertheless, in the first year after the crash, long-term bonds were still detectable, suggesting that the bats remembered previous individual relationships. Our findings are important for understanding the flexibility of animal societies in the face of dramatic changes and for the conservation of social mammals with declining populations.

  相似文献   
954.
A fetus with multiple structural defects was seen at prenatal ultrasound examination. After termination of the pregnancy a bilateral cleft lip, alveolus, and palate; micrognathia; and webbed joints were seen. Fetal tissues showed indications of infection, intranuclear inclusion bodies, chronic stress, haemolysis, arterial wall damage, and profuse haemorrhage. Parvovirus B19 DNA was detected in fetal tissues by dot hybridization after polymerase chain reaction. The possibility of parvovirus B19 infection leading to congenital malformations is discussed.  相似文献   
955.
956.
957.
958.
959.
    
Many species that inhabit seasonally ponded wetlands also rely on surrounding upland habitats and nearby aquatic ecosystems for resources to support life stages and to maintain viable populations. Understanding biological connectivity among these habitats is critical to ensure that landscapes are protected at appropriate scales to conserve species and ecosystem function. Biological connectivity occurs across a range of spatial and temporal scales. For example, at annual time scales many organisms move between seasonal wetlands and adjacent terrestrial habitats as they undergo life‐stage transitions; at generational time scales, individuals may disperse among nearby wetlands; and at multigenerational scales, there can be gene flow across large portions of a species’ range. The scale of biological connectivity may also vary among species. Larger bodied or more vagile species can connect a matrix of seasonally ponded wetlands, streams, lakes, and surrounding terrestrial habitats on a seasonal or annual basis. Measuring biological connectivity at different spatial and temporal scales remains a challenge. Here we review environmental and biological factors that drive biological connectivity, discuss implications of biological connectivity for animal populations and ecosystem processes, and provide examples illustrating the range of spatial and temporal scales across which biological connectivity occurs in seasonal wetlands.  相似文献   
960.
Fly ash samples from five power stations in Western Australia and Queensland, and two soils used for horticulture in Western Australia, were evaluated for a series of physical and chemical properties. Soils were comprised primarily of coarse sand-sized particles, whereas most of the fly ashes were primarily fine sand- and silt-sized particles. Hydraulic conductivities in the fly ashes were 105- to 248-fold slower than in the soils. The water-holding capacities of fly ashes at "field capacity" were three times higher than those of the soils. Extractable P in the fly ashes (except Tarong and Callide) were 20- to 88-fold higher than in the soils. The pH showed considerable variation among the different sources of fly ash, with samples from Muja being the most acidic (pH = 3.8; 1:5 in CaCl2 extract) and from Gladstone the most alkaline (pH = 9.9). The toxicity characteristic leaching procedure (TCLP) values indicate that the potential for release of trace elements from the fly ashes was well below regulatory levels. When applied at sufficient rates (e.g., to achieve 10% w/w in surface layers) to sandy soils, fly ash altered texture and increased water-holding capacity. Depending on the source of fly ash used, such amendments could also provide P and aid nutrient retention by increasing the phosphorus retention index (PRI) and/or cation exchange capacity (CEC). The considerable variability in physical and chemical properties among the fly ash samples evaluated in the present study supports the notion that field trials are essential to the future development of soil amendment strategies making use of any particular source of fly ash.  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