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   251564篇
  免费   15897篇
  国内免费   3478篇
林业   25396篇
农学   15310篇
基础科学   4324篇
  44018篇
综合类   28569篇
农作物   19339篇
水产渔业   17358篇
畜牧兽医   84311篇
园艺   8323篇
植物保护   23991篇
  2022年   2492篇
  2021年   3763篇
  2020年   4039篇
  2019年   4847篇
  2018年   4714篇
  2017年   5593篇
  2016年   5535篇
  2015年   5700篇
  2014年   7041篇
  2013年   17920篇
  2012年   8046篇
  2011年   9735篇
  2010年   9563篇
  2009年   9987篇
  2008年   8861篇
  2007年   7548篇
  2006年   7814篇
  2005年   6719篇
  2004年   6142篇
  2003年   5608篇
  2002年   4909篇
  2001年   5322篇
  2000年   4888篇
  1999年   4595篇
  1998年   4028篇
  1997年   4083篇
  1996年   3822篇
  1995年   4342篇
  1994年   3721篇
  1993年   3406篇
  1992年   3503篇
  1991年   3713篇
  1990年   3352篇
  1989年   3340篇
  1988年   2937篇
  1987年   2960篇
  1986年   2864篇
  1985年   3186篇
  1984年   3090篇
  1983年   2992篇
  1982年   2594篇
  1981年   2592篇
  1980年   2560篇
  1979年   2753篇
  1978年   2544篇
  1977年   2393篇
  1976年   2264篇
  1975年   2055篇
  1974年   2126篇
  1973年   2040篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
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   
44.
45.
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   
46.
47.
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   
48.
49.
The addition of molybdenum (0.05 mmol kg-1 dry-matter) to the diet of lambs given a trickle infection of Haemonchus contortus larvae (500 third stage larvae d-1 over six weeks) reduced mean faecal egg counts (epg) from 3952 to 2312 +/- 402 by 32 days (P less than 0.02) and greatly reduced the mean number of worms recovered from the abomasum 14 days after infection ceased (907 compared with 4167: P less than 0.01). Infection reduced haemoglobin concentrations less in lambs given molybdenum although the difference was small relative to the reduction in worm burden. Lambs not given molybdenum had low intraepithelial mast cell counts in the abomasal mucosa and less abomasal hypertrophy than expected from abomasal parasitism. Molybdenum did not consistently reduce the copper status of the host or the parasite. Previous exposure to molybdenum greatly reduced protein but not proteinase activity in, or secreted by, adult worms cultured for eight hours. It is suggested that molybdenum either increased the inflammatory response which preceded worm rejection or that it indirectly enhanced that reaction by reducing the effectiveness of copper-dependent, anti-inflammatory enzymes in the gastrointestinal mucosa.  相似文献   
50.
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   
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