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   211153篇
  免费   13657篇
  国内免费   649篇
林业   22879篇
农学   13821篇
基础科学   2930篇
  40356篇
综合类   12223篇
农作物   16979篇
水产渔业   15684篇
畜牧兽医   71891篇
园艺   6180篇
植物保护   22516篇
  2021年   2413篇
  2020年   2806篇
  2019年   3605篇
  2018年   3729篇
  2017年   4096篇
  2016年   4565篇
  2015年   4179篇
  2014年   5516篇
  2013年   16048篇
  2012年   4997篇
  2011年   6631篇
  2010年   6857篇
  2009年   7511篇
  2008年   6105篇
  2007年   5023篇
  2006年   5875篇
  2005年   5079篇
  2004年   4988篇
  2003年   4755篇
  2002年   4095篇
  2001年   4217篇
  2000年   3874篇
  1999年   4014篇
  1998年   3951篇
  1997年   4028篇
  1996年   3758篇
  1995年   4294篇
  1994年   3679篇
  1993年   3366篇
  1992年   3228篇
  1991年   3372篇
  1990年   3074篇
  1989年   3047篇
  1988年   2652篇
  1987年   2680篇
  1986年   2579篇
  1985年   2986篇
  1984年   2941篇
  1983年   2877篇
  1982年   2545篇
  1981年   2508篇
  1980年   2498篇
  1979年   2527篇
  1978年   2364篇
  1977年   2262篇
  1976年   2110篇
  1975年   1878篇
  1974年   1935篇
  1973年   1863篇
  1971年   1628篇
排序方式: 共有10000条查询结果,搜索用时 546 毫秒
31.
Osteomyelitis caused by Cryptococcus neoformans was diagnosed in a three-year-old male Irish wolfhound. The case details and radiological findings of radiolucency and periosteal reaction of the left third metatarsal bone had lead to an initial diagnosis of a malignant bone tumour. Biopsy revealed a fungal granuloma and culture identified the causal organism. A four month course of ketaconazole was instigated and the lameness resolved. Twelve months after the end of treatment there was no recurrence of the problem.  相似文献   
32.
33.
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   
34.
35.
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   
36.
37.
Behaviour of laying hens in a deep litter house   总被引:4,自引:0,他引:4  
1. Flocks of medium hybrid laying hens were housed in a modified deep litter system; the house was divided into 2, 3 and 4 pens in three successive years. Flock size was 300 or 370 and stocking density varied from 3.4 to 10.7 birds/m2. Higher densities used were above those recommended by the Ministry of Agriculture, Fisheries and Food (MAFF). 2. A random sample of 100 birds was identified with individual tags in each of the 9 flocks; regular observations using a scanning technique were made in each laying cycle to determine bird location and behaviour. 3. In all flocks the use of area by some individuals was uneven, that is, they were sighted in certain areas significantly more often than would have been expected by chance. The proportion of such individuals varied between flocks from 35 to 65%. Overall, birds spent more time on the slatted area than would have been expected from the area that it occupied. 4. A wide variety of different behaviour patterns was observed both on litter and on slats, but with foraging occurring more on litter and feeding more on slats. 5. Movement appeared to be constrained by crowding, because time spent in locomotion decreased in approximately linear fashion with increased stocking density. This provides support for MAFF recommendations of limits on stocking density in deep litter houses.  相似文献   
38.
在查清天津市园林主要花灌木刺吸口器害虫桃粉蚜、绣线菊蚜、棉蚜和山楂红蜘蛛发生消长规律的基础上 ,确定了防治适期和结合点 ,筛选出 10 %吡虫啉、绿灵、蚧螨灵、 1. 8%齐螨素和花保5种低、无毒药剂 ,防效均达到 90 %以上。查出天敌 13种 ,并对优势种作了取食量调查  相似文献   
39.
根据饲料可消化氨基酸研制肉仔鸡无鱼粉饲粮试验   总被引:1,自引:0,他引:1  
选用240只AA商品代出壳肉仔鸡进行试验,以探讨根据饲料中可消化氨基酸含量,研制菜籽粕型无鱼粉低蛋白肉仔鸡饲粮的饲用效果。结果表明:以可消化氨基酸为基础研制的菜籽粕型无鱼粉肉仔鸡低蛋白平衡饲粮,可降低饲粮蛋白质水平1-1.5个百分点,试验鸡49日龄体重达2158.26克、料肉比2.15:1,增重和饲料转化率均达到或接近鱼粉型高蛋白饲粮的效果;每吨菜籽粕型无鱼粉饲粮可比鱼粉型饲粮降低原料成本72-8  相似文献   
40.
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