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   39688篇
  免费   323篇
  国内免费   284篇
安全科学   905篇
废物处理   1938篇
环保管理   5413篇
综合类   5373篇
基础理论   11110篇
环境理论   8篇
污染及防治   10122篇
评价与监测   2855篇
社会与环境   2359篇
灾害及防治   212篇
  2022年   221篇
  2021年   263篇
  2020年   187篇
  2019年   271篇
  2018年   1775篇
  2017年   1685篇
  2016年   1768篇
  2015年   634篇
  2014年   802篇
  2013年   2590篇
  2012年   1362篇
  2011年   2471篇
  2010年   1656篇
  2009年   1618篇
  2008年   2116篇
  2007年   2502篇
  2006年   1282篇
  2005年   1038篇
  2004年   1122篇
  2003年   1062篇
  2002年   1064篇
  2001年   1279篇
  2000年   911篇
  1999年   531篇
  1998年   441篇
  1997年   386篇
  1996年   440篇
  1995年   469篇
  1994年   462篇
  1993年   408篇
  1992年   405篇
  1991年   363篇
  1990年   411篇
  1989年   397篇
  1988年   340篇
  1987年   305篇
  1986年   279篇
  1985年   281篇
  1984年   339篇
  1983年   334篇
  1982年   322篇
  1981年   308篇
  1980年   248篇
  1979年   275篇
  1978年   221篇
  1977年   200篇
  1975年   189篇
  1974年   166篇
  1973年   187篇
  1972年   217篇
排序方式: 共有10000条查询结果,搜索用时 757 毫秒
271.
Supplementing the nutrient requirement of crops through organic manures plays a key role in sustaining soil fertility, and crop productivity and reducing use of fossil fuels. Field experiments were conducted for 2 years at two different locations (i.e. Lucknow and Pantnagar) in Uttar Pradesh, India. The objectives of the study were to assess the herb and essential oil yields of Japanese mint (Mentha arvensis cv. Hy 77), and its nutrient accumulation under single and combined applications of organic manures and inorganic fertilizers (NPK). Changes in physical and chemical characteristics of the soils (Fluvisols, Mollisols) were also determined. Eight treatments comprising different combinations of NPK through inorganic fertilizers and farm yard manure (FYM) were compared. The distilled waste of mint after extraction of essential oil was recycled to soils in the plots to supplement the nutritional requirement of the succeeding mustard crop (Brassica juncea cv. Pusa Bold). Herb and essential oil yield of mint were significantly higher with combined application of organic and inorganic sources of nutrients as compared to single applications. Accumulation of N and P was at par under full inorganic and combined supply whereas, K accumulation was higher with the former. Soil organic C and pH after harvest of mint did not significantly differ among the treatments, but the level of mineralizable N, Olsen-P and NH4OAc extractable K were higher in soil with integrated supply of nutrients. Significant increase in soil water stable aggregates, organic C, available NPK and microbial biomass, and decrease in soil bulk density were observed with waste recycling over fertilizer application. These benefits were reflected in the seed and stubble yield of mustard which succeeded mint. This study indicates that combined application of inorganic fertilizers with organics helps in increasing the availability of nutrients and crop yield and provides a significant effect to the succeeding crop. Similarly, recycling crop residues reduces the need for fossil fuel based fertilizer, and helps in sustaining and restoring soil fertility in terms of available nutrients and major physical and chemical characteristics of the soil.  相似文献   
272.
The biological activity of the Matsucoccus spp. sex pheromones and diene modified analogs has been tested in forests of Israel and Portugal in order to explore the structure-activity relationship of the pine bast scale pheromone/kairomone system. The response of the adult predatory bugs, Elatophilus hebraicus and E. crassicornis and of the brown lacewing, Hemerobius stigma is more selective than that of the conspecific Matsucoccus males. The removal of the terminal methyl group from the diene terminus of both pheromones 1 and 2 eliminates all kairomonal activity but retains moderate pheromonal activity. Addition of a methyl group to the diene terminus of pheromones 1 and 2 sustains full pheromonal and kairomonal activities of the Elatophilus spp. but eliminates entirely the kairomonal activity of H. stigma. Subtle designed alterations in the structure of the diene group, typical of all Matsucoccus pheromones, change the mode of the kairomonal activity markedly.  相似文献   
273.
274.
275.
276.
277.
278.
279.
280.
Seleniummetabolisminanimalsandhumans¥P.D.Whanger(DepartmentofAgriculturalChemistry,OregonUniversity,Oregon97331-7301,USA)Abst...  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