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   19210篇
  免费   245篇
  国内免费   175篇
安全科学   607篇
废物处理   806篇
环保管理   2551篇
综合类   2975篇
基础理论   5214篇
环境理论   7篇
污染及防治   4882篇
评价与监测   1343篇
社会与环境   1114篇
灾害及防治   131篇
  2022年   159篇
  2021年   147篇
  2020年   151篇
  2019年   166篇
  2018年   276篇
  2017年   340篇
  2016年   451篇
  2015年   368篇
  2014年   576篇
  2013年   1509篇
  2012年   663篇
  2011年   900篇
  2010年   773篇
  2009年   763篇
  2008年   864篇
  2007年   914篇
  2006年   775篇
  2005年   674篇
  2004年   664篇
  2003年   638篇
  2002年   617篇
  2001年   736篇
  2000年   539篇
  1999年   312篇
  1998年   219篇
  1997年   266篇
  1996年   252篇
  1995年   286篇
  1994年   288篇
  1993年   223篇
  1992年   232篇
  1991年   212篇
  1990年   231篇
  1989年   211篇
  1988年   169篇
  1987年   177篇
  1986年   170篇
  1985年   178篇
  1984年   166篇
  1983年   166篇
  1982年   145篇
  1981年   150篇
  1980年   134篇
  1979年   140篇
  1978年   112篇
  1977年   116篇
  1975年   92篇
  1974年   90篇
  1973年   98篇
  1972年   90篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
A simple method of time series analysis, based upon linear least squares curve fitting, is developed. The method's advantages and disadvantages are discussed, and an example is presented using the Vostok Core methane record.  相似文献   
172.
The paper focuses upon the organization of a federal state-funded pollution prevention project in the Styrian industry. The project includes 13 companies from the textile, pulp and paper, machine building, wood working and printed circuit board manufacturing industries, covering most of the sectors and sizes in the Styrian industry. It started in January 1994 and will last for one year. It will demonstrate the possibilities of pollution prevention and the need for further research work. This project will make use of the methods and tools that were refined in the Austrian Prepare project. As a first step, a systematic balance of all the inputs and outputs of a company is made, after which the weak points and inefficiencies of material and energy use are identified and the options for improvements, both economical and ecological, are defined. Consequently, modifications in products and production lead to a situation with less waste and emissions. The preliminary lessons from these projects are presented: as a rule, the utilities (consumption of process materials and water, cleaning, energy, preparatory and finishing steps) are treated as black boxes and usually represent a considerable optimization potential. In these areas especially there is usually a lack of information and coordination as well as a need for a systematic and comprehensive approach. Leadership in the company and creative consultants are needed for starting lasting successful pollution prevention projects.  相似文献   
173.
The 57-MW high-flux reactor of the Institute Max von Laue-Paul Langevin at Grenoble serves as a central neutron-beam facility for laboratories and research institutes in the three member countries, the United Kingdom, France, and the Federal Republic of Germany. The heavy-water-moderated and -cooled reactor is equipped with hot, thermal, and cold moderators, providing neutrons with high intensity over an unusual wide range of energies (wavelengths) extending from some 0.1 meV (30 Å) up to some 500 meV (0.4 Å). An extensive system of neutron guides with different curvatures permits the transport of neutrons over distances ranging up to 140 m with minimal intensity losses for neutrons in the useful wavelength band. The transmitted beams, in addition, exhibit very low background contamination by fast and epithermal neutrons, and γ-radiation. A large variety of high-resolution neutron spectrometers provide unique opportunities in fields such as nuclear physics, crystallography, solid-state physics, chemistry, metallurgy, and biology.  相似文献   
174.
The distribution of actinomycetes in oil contaminated sandy loam ultisols of the Niger Delta region of Nigeria was studied to aid in understanding the effect of hydrocarbons on indigenous microbial population in tropical soils. The average total counts of actinomycetes in all the oil samples analysed was 103 cfu/g. Higher counts of actinomycetes were observed during the dry season than during the wet season. The counts of hydrocarbonoclastic actinomycetes correlated positively with the total count of actinomycetes.The actinomycetes were generally restricted to the top soil(0-10 cm soil depth) although a seemingly deeper(down to 40 cm soil depth) distribution was noticed in the dry season. The isolates included oil degrading species of Actinoplanes, Norcadia,Streptomyces and Streptosporangium. Their high oil utilization ability indicates their positive potential and role in the bioremediation of oil-spilled soils.  相似文献   
175.
176.
Only three decades ago it was thought inconceivable that organic compounds could transport electric charges like metals do. However, recently organic molecules exhibiting high conductivities have been synthesized. Some examples of organic conductors are presented together with the present status of this research which is both interesting to chemists and physicists. Some applications of organic conductors are discussed.  相似文献   
177.
178.
179.
180.
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