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   312579篇
  免费   17276篇
  国内免费   685篇
林业   24577篇
农学   14233篇
基础科学   3007篇
  46397篇
综合类   38685篇
农作物   17471篇
水产渔业   18232篇
畜牧兽医   135656篇
园艺   6522篇
植物保护   25760篇
  2019年   3732篇
  2018年   4331篇
  2017年   4710篇
  2016年   5060篇
  2015年   4521篇
  2014年   5872篇
  2013年   16621篇
  2012年   7856篇
  2011年   10196篇
  2010年   8012篇
  2009年   8395篇
  2008年   9434篇
  2007年   8654篇
  2006年   9135篇
  2005年   8330篇
  2004年   8145篇
  2003年   7857篇
  2002年   7279篇
  2001年   8551篇
  2000年   8139篇
  1999年   7207篇
  1998年   4389篇
  1997年   4427篇
  1996年   4154篇
  1995年   4792篇
  1994年   4240篇
  1993年   3935篇
  1992年   5849篇
  1991年   6156篇
  1990年   5977篇
  1989年   5882篇
  1988年   5358篇
  1987年   5449篇
  1986年   5411篇
  1985年   5527篇
  1984年   4952篇
  1983年   4476篇
  1982年   3482篇
  1981年   3296篇
  1980年   3239篇
  1979年   4370篇
  1978年   3742篇
  1977年   3363篇
  1976年   3089篇
  1975年   3062篇
  1974年   3656篇
  1973年   3654篇
  1972年   3401篇
  1971年   3231篇
  1970年   3082篇
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
131.
Mid-storage hydration-dehydration treatments with medium-vigour lettuce seed very effectively reduced physiological deterioration in storage and ultimately showed better field emergence and final yield. Soaking-drying treatment of high-vigour lettuce seed was not effective. Pre-sowing treatment of medium-vigour lettuce seed, though less effective than mid-storage treatment, gave better field performance, but high-vigour seed did not benefit from the treatment. For carrot, both mid-storage and pre-sowing seed treatments proved beneficial, with the former showing better performance than the latter. Unlike lettuce, well-preserved carrot seed responded positively to the pre-sowing treatment.  相似文献   
132.
Washed and unwashed red blood cells (RBC) from young calves, adult cattle, hamsters and humans were incubated with Leptospira interrogans serovars pomona and ballum. Washed cells suspended in saline were always haemolysed while unwashed cells and those which were washed and resuspended in plasma were never haemolysed, despite the presence of large numbers of organisms within the culture supernatant. Pomona produced greater haemolysis of cattle and human RBC than did ballum, but with hamster RBC ballum produced greater haemolysis than did pomona. A group of 6- to 9-month-old cattle infected with pomona showed no signs of clinical disease and RBC taken from them before infection and during the development of antibodies to pomona were haemolysed by pomona only after the cells were washed. Plasma therefore appears to have a protective function. This in vitro protective function of plasma even extended to plasma from young seronegative calves.  相似文献   
133.
Vanilla is a large genus of about 110 species in the orchid family (Orchidaceae), including the species Vanilla planifolia from which commercial vanilla flavoring is derived. Since most species of vanilla are considered rare and endangered there is an urgent need to conserve them through genetic analysis and propagation/conservation studies on this crop.The present study investigated the genetic diversity among nine leafy- and leaf-less Vanilla species employing 30 decamer RAPD primers and 10 ISSR primers. The species under study were diverse and displayed a range of variability (0–66% and 0–81% for RAPD and ISSR, respectively). A total of 154 RAPD polymorphic markers (83.24%, h = 0.378) and 93 ISSR polymorphic markers (86.11%, h = 0.363) were used to generate a genetic similarity matrix followed by the cluster analysis. Specific groupings were revealed by each cluster analysis with slight variation between two different markers. Among the nine species studied, V. planifolia, Vanilla aphylla and Vanilla tahitensis revealed very low level of variation within their collections, thus indicating a narrow genetic base. The large genetic distance of Vanilla andamanica from other species suggests its different origin. A close genetic affinity was observed between the pairs V. planifolia, V. tahitensis and Vanilla albida, V. aphylla. These are the first comparative results for RAPD and ISSR reporting inter-relationship among nine cultivated, wild and hybrid Vanilla species.  相似文献   
134.
135.
136.
Ohne Zusammenfassung  相似文献   
137.
138.
139.
140.
Ohne Zusammenfassung  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