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   3970篇
  免费   247篇
  国内免费   2篇
林业   332篇
农学   78篇
基础科学   17篇
  676篇
综合类   648篇
农作物   171篇
水产渔业   359篇
畜牧兽医   1517篇
园艺   120篇
植物保护   301篇
  2023年   40篇
  2022年   62篇
  2021年   101篇
  2020年   126篇
  2019年   155篇
  2018年   150篇
  2017年   119篇
  2016年   134篇
  2015年   96篇
  2014年   142篇
  2013年   202篇
  2012年   262篇
  2011年   326篇
  2010年   171篇
  2009年   156篇
  2008年   269篇
  2007年   270篇
  2006年   227篇
  2005年   206篇
  2004年   191篇
  2003年   197篇
  2002年   150篇
  2001年   34篇
  2000年   23篇
  1999年   46篇
  1998年   29篇
  1997年   18篇
  1996年   18篇
  1995年   15篇
  1994年   18篇
  1993年   15篇
  1992年   20篇
  1991年   22篇
  1990年   19篇
  1989年   14篇
  1988年   18篇
  1986年   12篇
  1985年   10篇
  1984年   16篇
  1983年   7篇
  1982年   10篇
  1981年   8篇
  1980年   6篇
  1978年   6篇
  1976年   5篇
  1974年   6篇
  1971年   6篇
  1928年   5篇
  1925年   6篇
  1924年   6篇
排序方式: 共有4219条查询结果,搜索用时 15 毫秒
51.
52.
53.
54.
55.
56.
The applicability of commercially available remote sensing instrumentation was evaluated for site-specific management of abiotic and biotic stress on cotton (Gossypium hirsutum L.) grown under a center pivot low energy precision application (LEPA) irrigation system. This study was conducted in a field where three irrigation regimes (100%, 75%, and 50% ETc) were imposed on areas of Phymatotrichum (root rot) with the specific objectives to (1) examine commercial remote sensing instrumentation for locating areas showing biotic and abiotic stress symptomology in a cotton field, (2) compare data obtained from commercial aerial infrared photography to that collected by infrared transducers (IRTs) mounted on a center pivot, (3) evaluate canopy temperature changes between irrigation regimes and their relationship to lint yield with IRTs and/or IR photography, and (4) explore the use of deficit irrigation and the use of crop coefficients for irrigation scheduling. Pivot-mounted IRTs and an IR camera were able to differentiate water stress among irrigation regimes. The IR camera distinguished between biotic (root rot) and abiotic (drought) stress with the assistance of groundtruthing. The 50% ETc regime had significantly higher canopy temperatures than the other two regimes, which was reflected in significantly lower lint yields when compared to the 75% and 100% ETc regimes. Deficit irrigation down to 75% ETc had no impact on lint yield, indicating that water savings were possible without reducing yield.  相似文献   
57.
Beef cattle producers seldom use fertilizers for their pastures in tropical regions of Brazil. Slowly, this is changing but because of the need for repeated applications, N fertilizer is rarely applied. The introduction of a forage legume is an appropriate solution for this problem, but until recently adoption has been very low as the legumes generally have not persisted in the sward. We report research on how grazing management can affect the persistence of stoloniferous legumes in pastures of Brachiaria spp. and the problems of establishing and maintaining crown-forming legumes such as Stylosanthes spp. With suitable management, milk or bovine carcass yields can be equal or greater from mixed than from grass-alone pastures fertilized with 120 or 150 kg Nha-1 year−1. In addition to savings in CO2 emissions from fossil fuels for the production and distribution of N fertilizers, nitrous oxide emissions from cattle excreta and legume residues are lower than those from N-fertilized brachiaria grass monocultures. Other studies indicate that enteric methane emissions from cattle may be mitigated when forage legumes are included in their diet. The use of forage legumes in mixed pastures for tropical regions is emerging as a feasible strategy to keep meat and milk production at acceptable levels with reduced greenhouse gas emission rates.  相似文献   
58.
Plant Foods for Human Nutrition - Sorghum is a major cereal crop with various agronomic advantages, contains health-promoting compounds and is gluten-free. There is a growing tendency to use...  相似文献   
59.
60.
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