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   194687篇
  免费   11280篇
  国内免费   108篇
林业   8275篇
农学   7087篇
基础科学   1318篇
  25416篇
综合类   28579篇
农作物   7793篇
水产渔业   10473篇
畜牧兽医   101756篇
园艺   2658篇
植物保护   12720篇
  2020年   1661篇
  2019年   2032篇
  2018年   3216篇
  2017年   3595篇
  2016年   3376篇
  2015年   2894篇
  2014年   3597篇
  2013年   8133篇
  2012年   6230篇
  2011年   7604篇
  2010年   5111篇
  2009年   5066篇
  2008年   7355篇
  2007年   7016篇
  2006年   6729篇
  2005年   5970篇
  2004年   5748篇
  2003年   5801篇
  2002年   5353篇
  2001年   6719篇
  2000年   6542篇
  1999年   5202篇
  1998年   2107篇
  1997年   2130篇
  1996年   1894篇
  1995年   2236篇
  1994年   1918篇
  1993年   1911篇
  1992年   3925篇
  1991年   4134篇
  1990年   4036篇
  1989年   4058篇
  1988年   3672篇
  1987年   3624篇
  1986年   3602篇
  1985年   3415篇
  1984年   2787篇
  1983年   2431篇
  1982年   1654篇
  1979年   2380篇
  1978年   1889篇
  1977年   1613篇
  1976年   1573篇
  1975年   1761篇
  1974年   2030篇
  1973年   2045篇
  1972年   1942篇
  1971年   1775篇
  1970年   1839篇
  1969年   1756篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
Prevention of renal carriage of leptospirosis in dogs by vaccination   总被引:1,自引:0,他引:1  
Dogs vaccinated with a Leptospira interrogans vaccine containing serogroups Canicola and Icterohaemorrhagiae and prepared from cultures grown in a protein-free medium resisted challenge with heterologous representatives of these serogroups. In contrast, control dogs were pyrexic and leptospires were isolated from the blood for nine days following Canicola challenge and six days after Icterohaemorrhagiae challenge. Leptospires were isolated from the urine of controls throughout the post challenge period and from kidneys at post mortem examination of six out of six and four out of six Canicola and Icterohaemorrhagiae challenged controls, respectively. There have been no reports of hypersensitivity reactions to this vaccine since its introduction in 1980.  相似文献   
112.
GRAY  S. J.; PRICE  COLIN 《Forestry》1990,63(2):161-175
Traditional forest economics deals with regularly-ordered activities.For many reasons, however, choices must often be made amongconflicting operational priorities. In these circumstances,maximizing net discounted revenue per hectare does not maximizeglobal profit. Priorities for action should be chosen in orderof urgency index ratio, defined as the cost of delaying an operationdivided by the units of limited resource needed to undertakethe operation. Forest managers tend to use informal and sometimesconflicting rules to assign priorities among uses of limitedresources. These priorities often differ from those indicatedby urgency index ratio. Urgency index ratio can be determinedby simple calculations based on readily-available data. Theconcept can be extended to include multiple constraints.  相似文献   
113.
Whereas the rise in temperature during the past 30–40 years has already had clear impacts on the phenology of fruit trees and pathogenic insects, there is a lack of such correlations for fungal pathogens. An examination of fruit rots indicates that pathogenic fungi react differentially to climate change due to their complex infection biology. The appearance of the black rot fungus Diplodia seriata in Northwestern Europe is best explained by rising temperatures during the vegetation period. An increase in fruit rot caused by Nectria galligena is anticipated when milder and more humid winter months favour canker formation on twigs and branches, thereby increasing inoculum for fruit infections. An increasing importance of Neofabraea alba and Glomerella cingulata and/or G.??acutata as storage rots of apples in Northern Germany cannot be safely correlated with the climate change at present. Research on fungi is currently being expanded at the OVB Jork in order to ensure a faster identification of new pathogens and a more thorough investigation of relevant features of their infection biology.  相似文献   
114.
Softening process and total antioxidant activity were evaluated in kiwifruit differently exposed to light intensity and harvested at two different times (October 10 and November 14). Fruit was stored for 2 months at 0 °C (S1) and then maintained for a week at ambient temperature (S2). The results showed that fruit harvested later presented a faster softening rate during storage than fruit harvested earlier, even if antioxidant activity did not change. Light-exposed fruit showed higher flesh firmness than that of shaded ones. Polygalacturonase activity was higher in kiwifruit maintained for a week at ambient temperature after cool storage and, in particular the highest value was recorded in fruit harvested later. The behaviour of β-galactosidase was different: it did not show changes in fruit harvested later and significantly decreased in light- and shade-exposed fruit harvested earlier.  相似文献   
115.
116.
117.
118.
119.
120.
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