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   32024篇
  免费   388篇
  国内免费   244篇
安全科学   987篇
废物处理   1175篇
环保管理   4805篇
综合类   4902篇
基础理论   9119篇
环境理论   23篇
污染及防治   8214篇
评价与监测   1894篇
社会与环境   1315篇
灾害及防治   222篇
  2022年   196篇
  2021年   197篇
  2019年   243篇
  2018年   430篇
  2017年   416篇
  2016年   618篇
  2015年   536篇
  2014年   727篇
  2013年   2415篇
  2012年   943篇
  2011年   1370篇
  2010年   1125篇
  2009年   1147篇
  2008年   1389篇
  2007年   1453篇
  2006年   1304篇
  2005年   1095篇
  2004年   1071篇
  2003年   1032篇
  2002年   1022篇
  2001年   1293篇
  2000年   913篇
  1999年   574篇
  1998年   462篇
  1997年   463篇
  1996年   485篇
  1995年   528篇
  1994年   468篇
  1993年   441篇
  1992年   448篇
  1991年   391篇
  1990年   404篇
  1989年   428篇
  1988年   373篇
  1987年   318篇
  1986年   295篇
  1985年   334篇
  1984年   314篇
  1983年   346篇
  1982年   348篇
  1981年   302篇
  1980年   271篇
  1979年   286篇
  1978年   252篇
  1977年   207篇
  1976年   209篇
  1975年   198篇
  1974年   180篇
  1973年   179篇
  1972年   206篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
The development of traceability in low-level radioactivity measurements is discussed. The role that the development of large quantities of natural matrix standards can play is also discussed.  相似文献   
92.
93.
94.
95.
96.
In the UK for the period 1994-99, a broad range of environmental projects were given financial support through the European Agriculture Guidance and Guarantee Fund under the Objective 1 and Objective 5b programmes. This paper is concerned with the ex-post evaluation of these projects set within a Sustainable Development framework. The aim was to identify project types or characteristics that offered the greatest return on investment. A classification of six broad project types was adopted. The evaluation revealed that there were significant differences between individual projects with respect to the type and scale, and temporal and social distribution of the benefits they delivered. In particular, as well as delivering environmental and economic benefits, many projects made a significant contribution to the development of human and social capital. The paper concludes that it is possible to improve the basis for future project selection in order to maximise the returns on environmental investments in the context of sustainable development.  相似文献   
97.
This article does not focus on adaptation or mitigation policy directly but on an allied opportunity that exists for the Pacific Islands via the auspices of the Climate Convention, because the existing very costly energy systems used in the Pacific Island region are fossil-fuel dependent. It is argued here that efforts can be made towards the development of energy systems that are ecologically sustainable because Pacific Island nations are eligible to receive assistance to introduce renewable energy technology and pursue energy conservation via implementation mechanisms of the Climate Convention and, in particular, through transfer of technology and via joint implementation. It is contended that assistance in the form of finance, technology, and human resource development from developed countries and international organizations would provide sustainable benefits in improving the local Pacific Island environments. It is also emphasized that mitigation of greenhouse gas emissions is not the responsibility of the Pacific Islands as they contribute very little on a per capita global scale and a tiny proportion of total global greenhouse gas emissions.  相似文献   
98.
ABSTRACT: Recent studies suggest that waste generation from the freshwater phase of Atlantic salmon (Salmo salar L.) production varies considerably on an annual basis. A fish farm on the West Coast of Scotland was visited regularly during a two-year period to determine inflow and outflow water quality. Waste output budgets of suspended solids (SS), biochemical oxygen demand (BOD), total nitrogen (TN), total phosphorus (TP), total ammonia nitrogen (TAN = NH3+NH4+), dissolved reactive phosphorus (DRP) and total phosphorus (TP) were produced. The annual waste loadings obtained were 71 kg TN t fish?1 yr?1 (one year of data only), 10.9–11.1 kg TP t fish?1 yr?1, 1.2–2.1 kg DRP t fish?1 yr?1, 422–485 kg BOD5 t fish?1 yr?1, 327–337 kg SS t fish?1 yr?1, and 30–35 kg TAN-N t fish?1 yr?1. Simple linear regression models relating waste parameter production to water temperature and feeding regime were developed. When compared to existing data for other salmonid production systems, greater ranges of daily waste loadings were observed. Wide variations in concentrations of these parameters during a daily cycle were also observed, suggesting that mass balance estimates of waste production will provide more robust estimates of waste output than frequent monitoring of outflow water quality.  相似文献   
99.
Starch-PVOH cast films were prepared with and without crosslinking agent (hexamethoxymethylmelamine) in the absence of plasticizer. Moisture absorption in films without crosslinking agent at a low relative humidity was similar to that of PVOH and increased as the relative humidity increased. Films with crosslinking agent showed moisture absorption linearly proportional to the relative humidity. Significant improvement in resistance to water disintegration for crosslinked starch-PVOH films was observed. While the tensile strength decreased with increased relative humidity, crosslinking significantly improved the tensile strength. Increased PVOH content improved elongation of films even when the relative humidity was 80% or higher. Biodegradation studies revealed that the degradation rate was negatively correlated with the PVOH content in films and crosslinking generated more converged degradation curves. Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by USDA implies no approval of the product to the exclusion of others that may also be suitable.  相似文献   
100.
Biological and physicochemical approaches were utilized in a treatment train for acid mine dis charge (AMD) waters. Anaerobic bioreactors, chemical precipitation reactors, and biopolymer chelation reactors, operated in static, semicontinuous, and continuous flow modes, removed significant quantities of metals and sulfates associated with AMD water. Static tests indicated accept able copper removal via precipitation by generation of hydrogen sulfide in anaerobic reactors. However, low pH affected the biopolymer coating in the chelation reactor, resulting in loss of bed surface. Corrections of AMD to pH > 7 resulted in some metal precipitationprior to biopolymer treatment. A series of static semicontinuous tests at pH 5.0 provided improved metal and sulfate removal. Copper (Cu+) was reduced to trace concentrations, while manganese (Mn+), although reduced, proved to be the most recalcitrant of the metals. © 2006 Wiley Periodicals, Inc.  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