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   254008篇
  免费   14824篇
  国内免费   672篇
林业   23573篇
农学   14039篇
基础科学   2974篇
  42633篇
综合类   26039篇
农作物   17299篇
水产渔业   16979篇
畜牧兽医   95931篇
园艺   6379篇
植物保护   23658篇
  2021年   2484篇
  2020年   2910篇
  2019年   3676篇
  2018年   3950篇
  2017年   4283篇
  2016年   4766篇
  2015年   4344篇
  2014年   5730篇
  2013年   16331篇
  2012年   6088篇
  2011年   8033篇
  2010年   7319篇
  2009年   7886篇
  2008年   7420篇
  2007年   6526篇
  2006年   7183篇
  2005年   6394篇
  2004年   6335篇
  2003年   6092篇
  2002年   5479篇
  2001年   5616篇
  2000年   5339篇
  1999年   5130篇
  1998年   4121篇
  1997年   4191篇
  1996年   3870篇
  1995年   4460篇
  1994年   3841篇
  1993年   3546篇
  1992年   4121篇
  1991年   4308篇
  1990年   4075篇
  1989年   4069篇
  1988年   3636篇
  1987年   3670篇
  1986年   3545篇
  1985年   3881篇
  1984年   3614篇
  1983年   3456篇
  1982年   2867篇
  1981年   2769篇
  1980年   2747篇
  1979年   3217篇
  1978年   2860篇
  1977年   2680篇
  1976年   2493篇
  1974年   2654篇
  1973年   2638篇
  1972年   2423篇
  1971年   2382篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
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   
23.
24.
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   
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.
对5个无核葡萄品种的试验表明,不同培养方式对离体胚发育的影响是很明显的,其中4个品种胚发育率液体培养高于固体培养,‘京早晶’在液体培养中胚发育率高达73.7%,是目前国内外胚发育率最高的报道;液体培养比固体培养胚的发育程度高,发育整齐,无畸形胚,易成苗.  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