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   19508篇
  免费   223篇
  国内免费   169篇
安全科学   642篇
废物处理   725篇
环保管理   3143篇
综合类   2862篇
基础理论   5213篇
环境理论   11篇
污染及防治   5008篇
评价与监测   1198篇
社会与环境   966篇
灾害及防治   132篇
  2022年   131篇
  2021年   154篇
  2020年   128篇
  2019年   181篇
  2018年   262篇
  2017年   281篇
  2016年   425篇
  2015年   303篇
  2014年   426篇
  2013年   1673篇
  2012年   564篇
  2011年   788篇
  2010年   638篇
  2009年   642篇
  2008年   826篇
  2007年   865篇
  2006年   777篇
  2005年   617篇
  2004年   696篇
  2003年   638篇
  2002年   584篇
  2001年   763篇
  2000年   544篇
  1999年   327篇
  1998年   295篇
  1997年   253篇
  1996年   277篇
  1995年   294篇
  1994年   328篇
  1993年   265篇
  1992年   288篇
  1991年   257篇
  1990年   282篇
  1989年   264篇
  1988年   229篇
  1987年   196篇
  1986年   187篇
  1985年   193篇
  1984年   221篇
  1983年   214篇
  1982年   229篇
  1981年   215篇
  1980年   159篇
  1979年   180篇
  1978年   153篇
  1977年   142篇
  1975年   127篇
  1974年   125篇
  1973年   115篇
  1972年   142篇
排序方式: 共有10000条查询结果,搜索用时 862 毫秒
291.
292.
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   
293.
294.
Mitigation and Adaptation Strategies for Global Change -  相似文献   
295.
296.
We present a remarkable chain of events in which percutaneous umbilical cord sampling was performed in an attempt to clarify a situation of possible fetal sex chromosome mosaicism in an amniotic fluid culture and led to the discovery that the mother herself had a 45,X/46,XX/ 47.XXX chromosome constitution. This may have simply represented the chance concurrence of pseudo-mosaicism in the amniotic fluid culture of a woman with an abnormal sex chromosome constitution, but it is also possible that the 45,X colony was maternal in origin. Although clearly a most unusual circumstance, the possibility should be kept in mind when termination of a pregnancy is being considered because of apparent mosaicism in a prenatal diagnostic study.  相似文献   
297.
Fisheries management is the practice of analyzing and selecting options to maintain or alter the structure, dynamics, and interaction of habitat, aquatic biota, and man to achieve human goals and objectives. The theory of fisheries management is: managers or decision makers attempt to maximize renewable `output' from an aquatic resource by choosing from among a set of decision options and applying a set of actions that generate an array of outputs. Outputs may be defined as a tangible catch, a fishing experience, an existence value, or anything else produced or supported by renewable aquatic resources. Overall output is always a mix of tangible and intangible elements. However defined, management goals and objectives are essential components of fisheries management or any other field of renewable natural resource management. Reaching consensus on management goals and objectives has never been a simple task. Beyond the broad and often conflicting goals of an agency, managers must decide who should set specific management objectives — agency personnel, the public, or a combination of the two. Historically, rhetoric aside, fisheries managers in North America nearly always have consulted with professionals in governmental roles to set management objectives. In a strongly pluralistic society, this often resulted in protracted political and legal conflict. Increasingly, there are calls for use of risk assessment to help solve such ecological policy and management problems commonly encountered in fisheries management. The basic concepts of ecological risk assessment may be simple, but the jargon and details are not. Risk assessment (and similar analytical tools) is a concept that has evoked strong reactions whenever it has been used. In spite of the difficulties of defining problems and setting management objectives for complex ecological policy questions, use of risk assessment to help solve ecological problems is widely supported. Ecological risk assessment will be most useful (and objective) in political deliberations when the policy debate revolves around largely technical concerns. To the extent that risk assessment forces policy debate and disagreement toward fundamental differences rather than superficial ones, it will be useful in decision making.  相似文献   
298.
Dedicated to Prof. H. Autrum on the occasion of his 85th birthday.  相似文献   
299.
300.
This paper, based on the autonomy concept, continues to investigate hierarchical forms and spatial structure of ecosystems. The former can lead to limits for the selection of the component parts of an ecosystem and a distinction between its endogenous and exogenous variables; and the latter can be lead to a hypothesis of the space of an ecosystem: the space of an ecosystem = its habitat area + supporting area + impact area, and two characteristics of ecosystems, space-overlapping and the area of ecosystem space, have been further studied referring to human activities.  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