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   287600篇
  免费   15982篇
  国内免费   2492篇
林业   25661篇
农学   16562篇
基础科学   4444篇
  46184篇
综合类   34844篇
农作物   18114篇
水产渔业   17880篇
畜牧兽医   110844篇
园艺   6750篇
植物保护   24791篇
  2021年   3108篇
  2020年   3423篇
  2019年   4170篇
  2018年   4403篇
  2017年   4929篇
  2016年   5307篇
  2015年   5000篇
  2014年   6408篇
  2013年   17113篇
  2012年   7421篇
  2011年   9358篇
  2010年   8476篇
  2009年   8817篇
  2008年   8670篇
  2007年   7826篇
  2006年   8325篇
  2005年   7416篇
  2004年   6966篇
  2003年   6667篇
  2002年   5992篇
  2001年   6958篇
  2000年   6791篇
  1999年   6344篇
  1998年   4613篇
  1997年   4594篇
  1996年   4245篇
  1995年   4832篇
  1994年   4139篇
  1993年   3855篇
  1992年   4934篇
  1991年   5166篇
  1990年   4891篇
  1989年   4812篇
  1988年   4342篇
  1987年   4417篇
  1986年   4256篇
  1985年   4524篇
  1984年   4081篇
  1983年   3852篇
  1982年   3048篇
  1981年   2927篇
  1980年   2892篇
  1979年   3546篇
  1978年   3108篇
  1977年   2875篇
  1976年   2692篇
  1974年   2968篇
  1973年   2954篇
  1972年   2754篇
  1971年   2676篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
21.
In a feeding trial lasting for months Halothane-positive fattening pigs were put on a diet containing different concentrations of vitamin E and selenium. After a Myostress application vitamin E and selenium were additionally injected in order to examine stress resistance (CK-test) and regenerative capacity (histological examination of Musculus longissimus dorsi) of skeletal muscle. The study revealed that neither high dietary levels of vitamin E/selenium nor a vitamin E/selenium treatment applied after stress are capable of preventing stress related myopathy nor can they influence its healing up favourably.  相似文献   
22.
23.
46 one day old chickens, divided into five groups, were fed an alternately composed vitamin D3 ration during 36 days. In the group depleted of vitamin D3 the typical rickets were found. When treated with a standard ration (2000 I.U. vit. D3/kg food) after 15 days depletion of vitamin D3 the chickens showed control-group parameters within 3 weeks. Using 60,000 I.U. vitamin D3 after a period of 15 days depletion evoked rather an abrupt beginning of healing tendency accompanied by signs of intoxication which were enhanced in those chickens treated with 120,000 I.U. vitamin D3: increase in number of osteoblasts, calcification of osteoblastic mitochondrial membranes and endothelial cell membranes, as well as degeneration of osteoblasts together with a strong reaction of eosinophils. There did not occur necrosis of osteocytes or of bone structure. Erythrocytes, being embedded in ground substance without endothelial surrounding, was a common finding in every group.  相似文献   
24.
25.
Differences in gas exchange parameters i.e. carbon exchange rate (CER), transpiration (Tr), water vapor conductance (g) were investigated, under a controlled environment, in a semi-dwarf (SD) Triticum aestivum line, its tall (TL) near isoline and the Payne (PA) variety characterized by small leaves. The plants were maintained in: (a) optimal substrate moisture condition (CTR); (b) salinized by watering with a 0.12 m NaCl solution (SLT); (c) water stressed by withholding waterings during a period of six days (STR); (d) stressed and salinized during the same period and with the same saline solution (S + S). CER and Tr were negatively affected by the stresses; SLT and S + S treatments had a higher WUE compared to their respective controls CTR and STR.
SD line had a better performance in terms of CER and WUE, particularly when water and salt stresses interacted. Leaf anatomy and assimilation/internal CO2 concentration curves contributed to explaining the SD performance.  相似文献   
26.
The proximal straight tubules of the female mouse kidney exhibit heavy periodic acid Schiff (PAS) staining in their brush borders and numerous cytoplasmic granules. In the present study, the female DBA/2Cr mouse kidney was examined, using various fixatives (formalin, PFA, PLP, Zamboni's, Bouin, or Carnoy solution) and various staining methods (HE, PAS, alcian blue, periodic acid methenamine-silver (PAM), toluidine blue, azan, or Congo red). Under azan and PAM, the staining pattern of the brush border was similar to that of PAS, and few effects of the fixative were observed. Cytoplasmic granules were clearly detected with PAM as well as PAS. However, these granules were not detected with Carnoy solution. Furthermore, distribution of granules differed between PAS and PAM.  相似文献   
27.
28.
Abstract. A humoral antibody response was demonstrated by ELISA in rainbow trout immunized intraperitoneally with extracts from the branchiuran ectoparasite Argulus foliaceus. A similar immunization protocol produced a higher titre response in a rabbit. Both trout and rabbit identified several antigenic components on immunoblots. ELISA and immunoblotting indicated that rainbow trout and rabbit anti-A. foliaceus sera identified components from the parasitic copepods Lepeophtheirus salmonis and Caligus elongatus.  相似文献   
29.
30.
 以甜菜坏死黄脉病毒(BNYVV)内蒙分离物的总RNA为模板,通过反转录和PCR扩增获得75kDa通读蛋白基因54kDa片段的目的片段。  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