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   3425篇
  免费   26篇
  国内免费   37篇
安全科学   69篇
废物处理   173篇
环保管理   428篇
综合类   470篇
基础理论   1244篇
环境理论   2篇
污染及防治   688篇
评价与监测   208篇
社会与环境   197篇
灾害及防治   9篇
  2023年   12篇
  2022年   18篇
  2021年   21篇
  2020年   11篇
  2019年   23篇
  2018年   126篇
  2017年   137篇
  2016年   203篇
  2015年   68篇
  2014年   37篇
  2013年   71篇
  2012年   444篇
  2011年   245篇
  2010年   43篇
  2009年   58篇
  2008年   79篇
  2007年   94篇
  2006年   87篇
  2005年   412篇
  2004年   550篇
  2003年   418篇
  2002年   59篇
  2001年   52篇
  2000年   31篇
  1999年   33篇
  1998年   12篇
  1997年   16篇
  1996年   13篇
  1995年   16篇
  1994年   11篇
  1993年   9篇
  1992年   10篇
  1991年   9篇
  1990年   8篇
  1989年   9篇
  1988年   3篇
  1987年   5篇
  1984年   4篇
  1982年   5篇
  1981年   2篇
  1979年   4篇
  1975年   2篇
  1974年   2篇
  1972年   3篇
  1971年   2篇
  1968年   1篇
  1967年   1篇
  1966年   2篇
  1961年   1篇
  1957年   1篇
排序方式: 共有3488条查询结果,搜索用时 31 毫秒
991.
所罗门群岛的雨林组成与人类干扰的历史   总被引:1,自引:0,他引:1  
通过对所罗门群岛的实例研究,我们发现迄今为止被认为是未经开发的、原始的、原生的热带雨林实际上是以前的定居点,而且存在着广泛的林木清除和灌溉/轮垦农业.多学科的观察,如雨林生态学、森林分类学和制图学、人类植物学、土地利用史、口头传说、人种学和考古学等方面都支持我们的结论.这些观察与有关伐木后雨林更新情况的现代观点有关系,也修正了某些关于美拉尼西亚史前史和历史的人口统计学假设,并意味着要较好地理解雨林动态,必须进行植物学、考古学和社会人类学等跨学科的联系.  相似文献   
992.
The silk weave spun by hornet larvae before undergoing pupal metamorphosis is composed of fibers and sheets, both containing symbiotic bacteria. The bacteria are secreted from the silk gland and are glued to the secreted silk, which is made up of amino-acid polymers. In the dark, it possesses at first an electric current amounting to several hundred nanoamperes (nA) (i.e., a thermoelectric property), and a high electric capacitance of up to several milliFarads (mF). This electrical charge is used gradually by the developing pupa. The symbiotic bacteria penetrate through slits in the coat of the silk fibers to the core or into pockets in the sheets, where they gradually digest parts of the silk weave, thereby nullifying its mechanical properties and facilitating in due time the egress of the imago from the puparium.  相似文献   
993.

News and Comments

More European heritage awards  相似文献   
994.
Conservation biologists and other environmentalists confront five obstacles in building support for regulatory policies that seek to exclude or remove introduced plants and other non-native species that threaten to harm natural areas or the natural environment. First, the concept of “harm to the natural environment” is nebulous and undefined. Second, ecologists cannot predict how introduced species will behave in natural ecosystems. If biologists cannot define “harm” or predict the behavior of introduced species, they must target all non-native species as potentially “harmful”. an impossibly large regulatory task. Third, loss of species richness may constitute harm to an environment, but introduced organisms typically, generally, and significantly add to species richness in ecosystems. If species richness correlates with desirable ecosystem properties, moreover, such as stability and productivity, as some ecologists believe, then introduced organisms, by increasing species richness, would support those desirable properties. Fourth, one may plausibly argue that extinction constitutes environmental harm, but there is no evidence that non-native species, especially plants, are significant causes of extinction, except for predators in certain lakes and other small island-like environments. Fifth, while aesthetic, ethical, and spiritual values may provide a legitimate basis for invasive species policy, biologists often cite concepts such as “biodiversity” and ecosystem “health” or “integrity” to provide a scientific justification. To assert that non-native species threaten biodiversity or undermine ecosystem health, however, may be to draw conceptual entailments or consequences from definitions of “biodiversity” and “integrity” that arbitrarily exclude non-native species or make the presence of exotic species a per se indicator of decline.  相似文献   
995.
Natura 2000 is a network of natural sites whose aim is to preserve species and habitats of relevance in the European Union. The policy underlying Natura 2000 has faced widespread opposition from land users and received extensive support from environmentalists. This paper addresses the ethical framework for Natura 2000 and the probable moral assumptions of its main stakeholders. Arguments for and against Natura 2000 were analyzed and classified according to “strong” or “weak” versions of the three main theories of environmental ethics – anthropocentrism, biocentrism, and ecocentrism. Weak (intergenerational) anthropocentrism was found to underlie the Natura 2000 network itself and the positions of environmentalists, while strong (traditional) anthropocentrism pervaded the positions of economic developers. Land users seemed to fall somewhere between weak and strong anthropocentrism. The paper discusses the relation between ethics and different attitudes towards Natura 2000, highlighting some of the implications for the network’s ongoing implementation. It is shown that Natura 2000 achieves a strong reversal of the burden of proof from conservation to economic development and land use change under anthropocentrism. It is argued that the alleged theoretical divide between anthropocentrism and non-anthropocentrism in relation to the burden of proof does not seem to hold in practice. Finally, it is predicted that the weak versions of anthropocentrism, biocentrism, and ecocentrism, are likely to converge extensively in respect to nature conservation policy measures.“Charting the depths of law and policy disputes yield an understanding of ethical differences.” Paul B. Thompson (2002, p. 189).  相似文献   
996.
In addition to obviating the use of synthetic agrochemicals and emphasizing farming in accordance with agro-ecological guidelines, organic farming acknowledges the integrity of plants as an essential element of its natural approaches to crop production. For cultivated plants, integrity refers to their inherent nature, wholeness, completeness, species-specific characteristics, and their being in balance with their (organically farmed) environment, while accomplishing their “natural aim.” We argue that this integrity of plants has ethical value, distinguishing integrity of life, plant-typic integrity, genotypic integrity, and phenotypic integrity. We have developed qualitative criteria to ethically evaluate existing practices and have applied these criteria to assess whether current plant breeding and propagation techniques violate the integrity of crop plants. This process has resulted in a design of a holistic, scientific approach of organic plant breeding and seed production. Our evaluation has met considerable criticism from mainstream (crop) scientists. We respond to the following questions: (1). Can ethics be incorporated into objective crop sciences? (2). What is the nature of the intrinsic value of plants in organic farming? We argue that criteria to take integrity into account can only be assessed from a holistic perspective and we show that a holistic approach is needed to design such ethical notions in a consistent way. The ethical notions have been further elaborated by formulating human responsibility and respect towards crop plants. Responsibility and respect can only be shown by providing crop plants the right to be nurtured and to express natural behavior at all levels of integrity.  相似文献   
997.
998.
This study uses a combination of data from U.K. monitoringstations and from modelling undertaken with the U.K.Meteorological Office's NAME Model to investigate therelative influences of primary and secondary particulateson total PM10 levels at sites in the United Kingdom. Co-located PM10 and sulphate aerosol measurementsindicate that sulphate has a disproportionately largeinfluence on the variation of PM10 levels incomparison to its contribution to their total mass.Comparisons of measured PM10 at urban centre, roadsideand rural sites suggest that local primary sources havevery little influence on daily mean levels. NAME has beenused to model both primary particles and sulphate aerosolfrom sources across the whole of Europe. The discrepanciesbetween modelled and observed PM10 suggest that coarseparticles, such as windblown dust and resuspended roaddust,may comprise a very large, if not dominant, proportion ofobserved PM10 levels. The apparently minor role ofprimary particles (especially locally-sourced ones) raisesa number of issues regarding the suitability of current U.K.and European legislation to addressing the particle problem.  相似文献   
999.
1000.
A new composite has been developed from natural rubber and chrome-tanned leather waste for use in footwear and textile industries. The contribution of this material to environmental quality and sustained development should be highligh because chrome tanned leather wastes, a major environmental problem, can be recycled. However, the safety of this new material for human use is questionable, as it is already well reported in the literature that chromium, particularly in its hexavalent oxidation state, can be genotoxic and carcinogenic to living beings. Thus, the aim of this study was to evaluate in vitro biocompatibility of this composite material for possible use in the footwear and textile industries, through cytotoxicity, cell adhesion, and genotoxicity tests. Inductively coupled plasma optical emission spectrometry (ICP-OES) was used to measure both concentrations of total and hexavalent chromium. Based on the findings, it was concluded that the composite exhibits low levels of cytotoxicity and genotoxicity, and possesses favorable properties for initial cell adhesion. Furthermore, it was verified that the composites released low concentrations of chromium and that the predominant species released would be trivalent chromium. The results of the present study open the possibility of the incorporation of solid residues of tanned leather into chromium without necessarily the chromium contained in these residues influences the toxicity and genotoxicity of this new material.  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