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   22186篇
  免费   274篇
  国内免费   135篇
安全科学   627篇
废物处理   954篇
环保管理   3140篇
综合类   3555篇
基础理论   6222篇
环境理论   12篇
污染及防治   5622篇
评价与监测   1375篇
社会与环境   925篇
灾害及防治   163篇
  2022年   143篇
  2021年   154篇
  2019年   148篇
  2018年   272篇
  2017年   301篇
  2016年   456篇
  2015年   358篇
  2014年   518篇
  2013年   1710篇
  2012年   645篇
  2011年   946篇
  2010年   750篇
  2009年   730篇
  2008年   920篇
  2007年   965篇
  2006年   863篇
  2005年   721篇
  2004年   701篇
  2003年   691篇
  2002年   659篇
  2001年   801篇
  2000年   600篇
  1999年   352篇
  1998年   287篇
  1997年   291篇
  1996年   297篇
  1995年   345篇
  1994年   318篇
  1993年   298篇
  1992年   293篇
  1991年   287篇
  1990年   302篇
  1989年   282篇
  1988年   256篇
  1987年   251篇
  1986年   231篇
  1985年   205篇
  1984年   263篇
  1983年   216篇
  1982年   279篇
  1981年   222篇
  1980年   190篇
  1979年   206篇
  1978年   184篇
  1977年   153篇
  1975年   144篇
  1974年   161篇
  1973年   162篇
  1972年   148篇
  1971年   146篇
排序方式: 共有10000条查询结果,搜索用时 484 毫秒
791.
792.
793.
The ecosystem services (ES) concept is being increasingly incorporated into environmental policy formulation and management approaches. The Corporate Ecosystem Services Review (ESR) is a framework used to assess the dependence and impact that a business has on ES. The success of the corporate experience of ES assessment provides an opportunity for adaption for local authority decision making. In this paper, the ESR tool was adapted to the South African setting at a local government level, and tested at two sites in the Msunduzi Municipality, KwaZulu-Natal. In testing the tool and gathering feedback from key stakeholders, it was found that there are both opportunities and challenges to this approach. Overall, however, it provides an opportunity for the systematic inclusion of ES assessment into existing regulatory frameworks for land-use planning and Integrated Environmental Management, whether in a strategic application, at a broader spatial (municipal) scale or in a specific locale within the municipality.  相似文献   
794.
795.
796.
797.
798.
799.
The aim of the present study is to investigate mechanical and morphological properties of pineapple leaf fibres (PALF) reinforced phenolic composites and its comparison with kenaf fibre (KF)/phenolic composites. Mechanical properties (tensile, flexural and impact) of untreated and treated PALF phenolic composites at different fibre loading were investigated. Tensile, flexural and impact properties of PALF and kenaf/phenolic composites were analyzed as per ASTM standard. Morphological analysis of tensile fracture samples of composites was carried out by scanning electron microscopy. Obtained results indicated that treated PALF/phenolic composites at 50% PALF loading exhibited better tensile, flexural and impact properties as compared to other untreated PALF/phenolic composites. Treated kenaf/phenolic composites at 50% fibre loading showed better tensile, flexural and impact properties than untreated kenaf/phenolic composite. It is concluded that treated 50% fibre loading kenaf and PALF/phenolic composites showed better mechanical properties than untreated kenaf and PALF/phenolic composites due to good fibre/matrix interfacial bonding. Results obtained in this study will be used for the further study on hybridization of PALF and KF based phenolic composites.  相似文献   
800.
The demand for biodegradable plastic material is increasing worldwide. However, the cost remains high in comparison with common forms of plastic. Requirements comprise low cost, good UV-stability and mechanical properties, as well as solubility and water uptake lead to the preparation of multi-component polymer blends based on polyvinyl alcohol and starch in combination with waste products that are hard to utilize—waste lignin and hydrolysate extracted from chromium tanned waste. Surprisingly the addition of such waste products into PVA gives rise to blends with better biodegradability than commercial PVA in an aquatic aerobic environment with non-adapted activated sludge. These blends also exhibited greater solubility in the water and UV stability than commercial PVA. Tests on the processing properties of the blends (melt flow index, tensile strength and elongation at break of the films) as well as their mechanical properties showed that materials based on these blends might be applied in agriculture (for example as the systems for controlled-release pesticide or fertilizer) and, somewhat, in the packaging sector.  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