全文获取类型
收费全文 | 7816篇 |
免费 | 123篇 |
国内免费 | 398篇 |
专业分类
安全科学 | 225篇 |
废物处理 | 343篇 |
环保管理 | 648篇 |
综合类 | 1664篇 |
基础理论 | 1557篇 |
环境理论 | 4篇 |
污染及防治 | 2015篇 |
评价与监测 | 597篇 |
社会与环境 | 1219篇 |
灾害及防治 | 65篇 |
出版年
2023年 | 47篇 |
2022年 | 154篇 |
2021年 | 160篇 |
2020年 | 94篇 |
2019年 | 93篇 |
2018年 | 163篇 |
2017年 | 207篇 |
2016年 | 223篇 |
2015年 | 177篇 |
2014年 | 326篇 |
2013年 | 678篇 |
2012年 | 352篇 |
2011年 | 395篇 |
2010年 | 318篇 |
2009年 | 330篇 |
2008年 | 404篇 |
2007年 | 411篇 |
2006年 | 335篇 |
2005年 | 302篇 |
2004年 | 277篇 |
2003年 | 259篇 |
2002年 | 244篇 |
2001年 | 277篇 |
2000年 | 231篇 |
1999年 | 118篇 |
1998年 | 88篇 |
1997年 | 96篇 |
1996年 | 78篇 |
1995年 | 97篇 |
1994年 | 78篇 |
1993年 | 73篇 |
1992年 | 62篇 |
1991年 | 63篇 |
1990年 | 75篇 |
1989年 | 56篇 |
1988年 | 42篇 |
1987年 | 39篇 |
1986年 | 47篇 |
1985年 | 48篇 |
1984年 | 51篇 |
1983年 | 36篇 |
1982年 | 46篇 |
1981年 | 36篇 |
1980年 | 44篇 |
1979年 | 44篇 |
1974年 | 30篇 |
1973年 | 34篇 |
1972年 | 39篇 |
1971年 | 30篇 |
1969年 | 31篇 |
排序方式: 共有8337条查询结果,搜索用时 15 毫秒
991.
992.
993.
Sami M. Kivel? Panu V?lim?ki David Carrasco Maarit I. M?enp?? Satu M?ntt?ri 《Die Naturwissenschaften》2012,99(8):607-616
A resource allocation trade-off is expected when resources from a common pool are allocated to two or more traits. In holometabolous insects, resource allocation to different functions during metamorphosis relies completely on larval-derived resources. At adult eclosion, resource allocation to the abdomen at the expense of other body parts can be seen as a rough estimate of resource allocation to reproduction. Theory suggests geographic variation in resource allocation to the abdomen, but there are currently no empirical data on it. We measured resource allocation to the abdomen at adult eclosion in four geometrid moths along a latitudinal gradient. Resource (total dry material, carbon, nitrogen) allocation to the abdomen showed positive allometry with body size. We found geographic variation in resource allocation to the abdomen in each species, and this variation was independent of allometry in three species. Geographic variation in resource allocation to the abdomen was complex. Resource allocation to the abdomen was relatively high in partially bivoltine populations in two species, which fits theoretical predictions, but the overall support for theory is weak. This study indicates that the geographic variation in resource allocation to the abdomen is not an allometric consequence of geographic variation in resource acquisition (i.e., body size). Thus, there is a component of resource allocation that can evolve independently of resource acquisition. Our results also suggest that there may be intraspecific variation in the degree of capital versus income breeding. 相似文献
994.
995.
996.
997.
于2016年11、12月以北京市3个典型区域的431名普通居民为研究对象,平均年龄(62.80±10.42)岁.以液相色谱联合质谱检测人群尿液中2-OHNap、1-OHNap、2-OHFul、1+9-OHPhe、2-OHPhe、3-OHPhe、4-OHPhe及1-OHPyr浓度水平,并对研究人群进行问卷调查.结果表明,全部人群尿液中2-OHNap、1-OHNap、2-OHFul、∑OHPhe、1-OHPyr浓度中位数水平分别为2.99,3.46,4.24,1.49,0.35μg/g Cr.Logistics回归分析显示,吸烟者尿液中2-OHNap、1-OHNap、2-OHFul、1-OHPyr发生高浓度的可能性分别是不吸烟者的9.83,6.32,4.51,1.89倍;年龄组每增加一个等级,导致2-OHNap、1-OHNap、∑OHPhe、1-OHPyr发生高浓度的可能性分别增加了0.48,0.44,0.31,0.46倍;教育程度每增加一个等级,导致2-OHFul发生高浓度的可能性降低了0.44倍.相关性分析显示,人体尿液中2-OHNap的浓度与环境空气中的萘的浓度呈正相关关系.人体尿液中2-OHNap主要来源于城市空气中的萘.影响北京市典型区域人群尿样中羟基多环芳烃浓度升高的主要因素为吸烟、年龄增高以及受教育程度较低. 相似文献
998.
999.
Mark V. Lomolino J. Curtis Creighton Gary D. Schnell David L. Certain 《Conservation biology》1995,9(3):605-614
Field studies were conducted on the western population of the endangered American burying beetle (Nicrophorus americanus) in Oklahoma and Arkansas to determine its habitat affinities. A common cause of declining populations is some specialized adaptation that makes it difficult to respond to a rapidly changing habitat. We evaluated the hypothesis that N. americanus is a habitat specialist in its search for food, preferring mature forests with deep, humic soils. This hypothesis was rejected. Based on comparisons of niche breadth among syntopic congeners and niche overlap, N. americanus is relatively generalized in its use of a range of habitats when searching for food. It is likely that the generalist nature and the endangered status of N. americanus both derive from the fact that it is the largest member of its guild. In comparison to smaller species, N. americanus breeds on larger carcasses, which are more unpredictable in space and time. It is likely, therefore, that N. americanus must search over a larger area and greater diversity of habitats than its smaller congeners. 相似文献
1000.