全文获取类型
收费全文 | 17788篇 |
免费 | 242篇 |
国内免费 | 611篇 |
专业分类
安全科学 | 483篇 |
废物处理 | 849篇 |
环保管理 | 2131篇 |
综合类 | 2891篇 |
基础理论 | 4590篇 |
环境理论 | 2篇 |
污染及防治 | 4758篇 |
评价与监测 | 1270篇 |
社会与环境 | 1538篇 |
灾害及防治 | 129篇 |
出版年
2023年 | 118篇 |
2022年 | 260篇 |
2021年 | 202篇 |
2020年 | 150篇 |
2019年 | 193篇 |
2018年 | 300篇 |
2017年 | 316篇 |
2016年 | 458篇 |
2015年 | 346篇 |
2014年 | 526篇 |
2013年 | 1459篇 |
2012年 | 613篇 |
2011年 | 833篇 |
2010年 | 689篇 |
2009年 | 753篇 |
2008年 | 846篇 |
2007年 | 863篇 |
2006年 | 722篇 |
2005年 | 643篇 |
2004年 | 608篇 |
2003年 | 662篇 |
2002年 | 593篇 |
2001年 | 808篇 |
2000年 | 540篇 |
1999年 | 333篇 |
1998年 | 248篇 |
1997年 | 228篇 |
1996年 | 248篇 |
1995年 | 292篇 |
1994年 | 219篇 |
1993年 | 182篇 |
1992年 | 205篇 |
1991年 | 202篇 |
1990年 | 211篇 |
1989年 | 193篇 |
1988年 | 153篇 |
1987年 | 159篇 |
1986年 | 114篇 |
1985年 | 149篇 |
1984年 | 151篇 |
1983年 | 138篇 |
1982年 | 133篇 |
1981年 | 134篇 |
1980年 | 107篇 |
1979年 | 113篇 |
1977年 | 88篇 |
1975年 | 81篇 |
1974年 | 80篇 |
1973年 | 95篇 |
1972年 | 88篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
491.
河口湿地是陆海相互作用强烈的重要地球关键带,同时还受到人类活动的强烈影响.黄河三角洲湿地作为年轻的暖温带河口湿地,其微塑料污染状况尚未得到充分研究.因此对黄河三角洲湿地表层沉积物中微塑料的形态、丰度、粒径和成分组成进行了测定,并使用污染负荷指数(PLI)和潜在污染风险指数(PRI)评估了研究区域微塑料污染状况和生态风险.结果表明,黄河三角洲湿地微塑料丰度为20~520 n ·kg-1,中值为150 n ·kg-1.微塑料形貌以纤维和黑色为主,粒径在1 mm以上,成分多为人造丝、聚乙烯、聚酯纤维和聚对苯二甲酸乙二醇酯等.湿地中微塑料的PLI值介于0.04~0.96之间,PRI值介于0.00~171.60之间,表明黄河三角洲湿地微塑料污染处于轻微污染和低生态风险水平. 相似文献
492.
493.
494.
495.
Robert T. LackeyAuthor vitae 《Environmental Science & Policy》1998,1(4):329-335
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
496.
Hydroxyprogesterone caproate is one of the most effective and widely used drugs for the treatment of uterine bleeding and threatened miscarriage in women. Hydroxyprogesterone caproate was administered to pregnant rats in order to assess the effect of intraperitoneal exposure to supranormal levels of hydroxyprogesterone caproate on the male reproductive potential in the first generation. The cauda epididymal sperm count and motility decreased significantly in rats exposed to hydroxyprogesterone caproate during embryonic development, when compared with control rats. The levels of serum testosterone decreased with an increase in follicle stimulating hormone and luteinizing hormone in adult rats exposed to hydroxyprogesterone caproate during the embryonic stage. It was suggested that the impairment of male reproductive performance could be mediated through the inhibition of testosterone production. 相似文献
497.
498.
499.
500.