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   15601篇
  免费   113篇
  国内免费   162篇
安全科学   383篇
废物处理   654篇
环保管理   1684篇
综合类   3372篇
基础理论   3585篇
环境理论   9篇
污染及防治   4038篇
评价与监测   1224篇
社会与环境   852篇
灾害及防治   75篇
  2022年   159篇
  2021年   141篇
  2020年   93篇
  2019年   123篇
  2018年   206篇
  2017年   228篇
  2016年   348篇
  2015年   276篇
  2014年   479篇
  2013年   1165篇
  2012年   541篇
  2011年   668篇
  2010年   528篇
  2009年   587篇
  2008年   644篇
  2007年   644篇
  2006年   611篇
  2005年   540篇
  2004年   493篇
  2003年   490篇
  2002年   481篇
  2001年   617篇
  2000年   379篇
  1999年   271篇
  1998年   154篇
  1997年   172篇
  1996年   180篇
  1995年   198篇
  1994年   189篇
  1993年   137篇
  1992年   166篇
  1991年   175篇
  1990年   172篇
  1989年   143篇
  1988年   156篇
  1987年   96篇
  1986年   130篇
  1985年   127篇
  1984年   122篇
  1983年   116篇
  1982年   122篇
  1981年   121篇
  1980年   87篇
  1979年   99篇
  1978年   101篇
  1976年   93篇
  1974年   104篇
  1972年   87篇
  1967年   100篇
  1964年   93篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
221.
222.
Prenatal counselling for fetal agenesis of the corpus callosum is difficult as the prognosis until now has been so uncertain. We have reviewed the current world English literature to provide the best probabilistic information for prospective parents. In total, there are 70 cases where the diagnosis was made prenatally. The diagnosis of apparently isolated agenesis of the corpus callosum (in the absence of other sonographically detectable anomalies) appears to carry an excellent prognosis, with an 85 per cent chance of a normal developmental outcome and a 15 per cent risk of handicap. Fetal karyotyping is recommended as there is a 1 in 10 risk of aneuploidy. If other anomalies are detected prenatally, the outcome is very poor. Termination of pregnancy is advised in these circumstances.  相似文献   
223.
224.
225.
226.
227.
228.
229.
230.
Sustainable resource management is the critical agricultural research and development challenge in sub-Saharan Africa. The accumulated knowledge on soil management gathered over the last 10 years, combined with solid crop improvement and plant health research at farmers’ level, has brought us to a stage where we can now address with confidence the intensification of cereal–grain–legume-based cropping systems in the dry savanna of West Africa in a sustainable and environmentally positive manner.Two sustainable farming systems that greatly enhance the productivity and sustainability of integrated livestock systems have been developed and implemented in the dry savanna of Nigeria. These are: (i) maize (Zea mays L.)–promiscuous soybean [Glycine max (L.) Merr.] rotations that combine high nitrogen fixation and the ability to kill large numbers of Striga hermonthica seeds in the soil; and (ii) miflet [Eleusine coracana (L.) Gaerth] and dual-purpose cowpea [Vigna unguiculata (L.) Walp.]. Improvement of the cropping systems in the dry savanna has been driven by the adoption of promiscuously nodulating soybean varieties (in particular TGx 1448-2E) and dual-purpose cowpea. The rate of adoption is very high, even in the absence of an efficient seed distribution system. The number of farmers cultivating the improved varieties increased by 228% during the last 3 years. Increased production of promiscuous soybean has been stimulated by increased demand from industries and home utilization. Production in Nigeria was estimated at 405,000 t in 1999 compared to less than 60,000 t in 1984. Economic analysis of these systems shows already an increase of 50–70% in the gross incomes of adopting farmers compared to those still following the current practices, mainly continuous maize cultivation. Furthermore, increases in legume areas of 10% in Nigeria (about 30,000 ha in the northern Guinea savanna) and increases of 20% in yield have translated into additional fixed nitrogen valued annually at US$ 44 million. This reflects, at the same time, an equivalent increase in land-use productivity, and with further spread of the improved crops, there are excellent prospects for additional economic and environmental benefits from a very large recommendation domain across West Africa.  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