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   16598篇
  免费   169篇
  国内免费   139篇
安全科学   414篇
废物处理   717篇
环保管理   1956篇
综合类   2730篇
基础理论   4513篇
环境理论   6篇
污染及防治   4286篇
评价与监测   1155篇
社会与环境   1032篇
灾害及防治   97篇
  2022年   150篇
  2021年   131篇
  2020年   117篇
  2019年   126篇
  2018年   223篇
  2017年   261篇
  2016年   357篇
  2015年   295篇
  2014年   492篇
  2013年   1250篇
  2012年   544篇
  2011年   756篇
  2010年   659篇
  2009年   643篇
  2008年   722篇
  2007年   773篇
  2006年   631篇
  2005年   558篇
  2004年   567篇
  2003年   543篇
  2002年   525篇
  2001年   675篇
  2000年   492篇
  1999年   267篇
  1998年   190篇
  1997年   213篇
  1996年   220篇
  1995年   250篇
  1994年   244篇
  1993年   188篇
  1992年   204篇
  1991年   191篇
  1990年   214篇
  1989年   192篇
  1988年   155篇
  1987年   166篇
  1986年   159篇
  1985年   162篇
  1984年   156篇
  1983年   149篇
  1982年   131篇
  1981年   123篇
  1980年   116篇
  1979年   126篇
  1978年   102篇
  1977年   113篇
  1975年   88篇
  1974年   90篇
  1973年   98篇
  1972年   89篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
201.
202.
203.
204.
205.
206.
Several management practices are available to conserve and sequester C in the agricultural sector of the former Soviet Union (FSU). The highest rate of C accumulation would result from the implementation of a no-till management option which will only continue during the first ten years until new C equilibrium is reached. Agroforestry management options provide a longer period for C accumulation, but at a lower rate. It is possible that the longest period of C conservation may be achieved by increasing the area under perennial grasses in the crop rotation. During the first decade of implementation of the management practices, the amount of C conserved or sequestered would be approximately equal to the current rate of net C sequestration in FSU forest sector. At present, agricultural soils and vegetation of the FSU store approximately 120 Pg C; the accumulation of soil organic matter is 0.032 Pg C yr-1. The annual C loss in the FSU agricultural sector was estimated at 0.21 Pg C yr-1.  相似文献   
207.
208.
Focus on eco-friendly processing techniques makes vegetable tanning a viable option in leather processing and establishes the subsequent need for the more efficient methods of extraction in tannin manufacture. Application of ultrasound has been tried in the extraction of tannins from myrobalan nuts in order to improve the extraction efficiency, to perform the extraction under milder process conditions and to reduce the process time. The influence of process parameters such as ultrasonic output power, time and temperature has been studied. Scale-up trials and the use of ultrasound in pulse mode have also been attempted. The results show that a three- to fivefold improvement is possible with ultrasonic output from 20 to 100 W. Extraction efficiency has been calculated from the maximum extractable materials from myrobalan nuts. Extraction efficiency is found to be 90% for ultrasound, 100 W without external heating as compared to 77% for control process at 70 °C for 4 h. Therefore, ultrasound could be employed even dispensing with provision for temperature controls. The use of ultrasound in pulse mode offered 70% extraction efficiency of continuous mode. Scale-up trials indicate that there exists an optimum ultrasonic output power depending on the amount of nuts used, to achieve better extraction efficiency. The effectiveness of ultrasonically extracted tannin solution has also been tested in the tanning process for its applicability. The degree of tanning efficacy has been assessed by shrinkage temperature measurement. The results indicate that ultrasonically extracted tannin solution is suitable for tanning process. Therefore, application of ultrasound in tannin extract manufacture is a viable option with added advantages.  相似文献   
209.
210.
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