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   301288篇
  免费   17027篇
  国内免费   686篇
林业   24271篇
农学   14158篇
基础科学   3001篇
  45277篇
综合类   39667篇
农作物   17415篇
水产渔业   17567篇
畜牧兽医   126314篇
园艺   6421篇
植物保护   24910篇
  2019年   3695篇
  2018年   4191篇
  2017年   4612篇
  2016年   4920篇
  2015年   4435篇
  2014年   5780篇
  2013年   16382篇
  2012年   7272篇
  2011年   9488篇
  2010年   7770篇
  2009年   8216篇
  2008年   8841篇
  2007年   7842篇
  2006年   8408篇
  2005年   7594篇
  2004年   7461篇
  2003年   7209篇
  2002年   6594篇
  2001年   7829篇
  2000年   7565篇
  1999年   6587篇
  1998年   4315篇
  1997年   4384篇
  1996年   4122篇
  1995年   4826篇
  1994年   4301篇
  1993年   3950篇
  1992年   5675篇
  1991年   5996篇
  1990年   5664篇
  1989年   5622篇
  1988年   5073篇
  1987年   5291篇
  1986年   5341篇
  1985年   5418篇
  1984年   4723篇
  1983年   4433篇
  1982年   3382篇
  1981年   3193篇
  1980年   3140篇
  1979年   4197篇
  1978年   3701篇
  1977年   3223篇
  1976年   3083篇
  1975年   2998篇
  1974年   3483篇
  1973年   3595篇
  1972年   3374篇
  1971年   3275篇
  1970年   3111篇
排序方式: 共有10000条查询结果,搜索用时 17 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.
Ohne Zusammenfassung  相似文献   
136.
In addition to the well-defined phenolic estrogens in human pregnancy urine there appears to be another estrogenic substance which is a neutral non-ketonic compound.  相似文献   
137.
138.
139.
Ohne Zusammenfassung  相似文献   
140.
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