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   1027篇
  免费   94篇
林业   71篇
农学   37篇
基础科学   3篇
  178篇
综合类   84篇
农作物   42篇
水产渔业   98篇
畜牧兽医   516篇
园艺   23篇
植物保护   69篇
  2024年   4篇
  2023年   6篇
  2022年   16篇
  2021年   34篇
  2020年   47篇
  2019年   71篇
  2018年   35篇
  2017年   32篇
  2016年   46篇
  2015年   40篇
  2014年   36篇
  2013年   54篇
  2012年   71篇
  2011年   99篇
  2010年   46篇
  2009年   31篇
  2008年   56篇
  2007年   64篇
  2006年   52篇
  2005年   46篇
  2004年   48篇
  2003年   50篇
  2002年   46篇
  2001年   5篇
  2000年   10篇
  1999年   3篇
  1998年   6篇
  1997年   9篇
  1996年   8篇
  1995年   6篇
  1994年   5篇
  1993年   3篇
  1992年   5篇
  1988年   5篇
  1981年   1篇
  1980年   2篇
  1979年   2篇
  1978年   3篇
  1977年   1篇
  1976年   1篇
  1975年   1篇
  1974年   1篇
  1965年   1篇
  1962年   1篇
  1955年   1篇
  1941年   1篇
  1937年   1篇
  1936年   1篇
  1933年   1篇
  1931年   1篇
排序方式: 共有1121条查询结果,搜索用时 15 毫秒
1.
2.
A cohort of 53 swine seronegative to Aujeszky's disease virus (ADV) was monitored in a 1 year study of a chronically infected commercial Swedish weaner pig producing herd. Serum samples were acquired from all 134 adult swine and analyzed by enzyme-linked immmunosorbent assay (ELISA). Animals testing negative, along with introduced replacement gilts, were followed serologically every second month. Movements of animals were recorded for 319 days and exposure to seropositive animals was calculated for each seronegative pig in the cohort. The accumulated daily pig contact between the 53 ADV-non-infected swine and 43 infected swine was 35 660 days and the median number of days in contact for the non-infected swine with infected was 222. Despite the frequent contact with seropositive pigs, no seronegative animals seroconverted during the first 11 months of observation. Forty-six of 53 pigs seroconverted after a clinical outbreak during the twelfth month of observation.  相似文献   
3.
Extreme eosinophilia with disseminated eosinophilic granulomatous disease is described in a 4-year-old Arabian mare. Clinical signs included weight loss, coughing, jugular distention, and ventral edema. Cutaneous lesions were not observed. Eosinophilic inflammation was observed in cytologic specimens from the respiratory tract, body cavities, and lymph nodes. At necropsy, a 20-cm diameter intrathoracic mass was observed. Smaller nodules were present in the lymph nodes, liver, spleen, adrenal glands, pancreas, and skeletal muscle. Histologically, these masses and nodules were characterized by infiltrates of eosinophils, macrophages, and multinucleated giant cells, reactive fibroplasia; and multifocal eosinophilic coagula. Microscopically, mild eosinophilic infiltrates were observed in sections of stomach, small intestine, colon, and pleura; however, gross lesions were not observed in these tissues at necropsy. The etiology of the extreme eosinophilia and disseminated eosinophilic granulomatous disease in this horse was not determined.  相似文献   
4.
A method for monitoring tobacco whitefly [Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae)] populations was developed and used for timing spray applications against this pest in cotton. It was found to be successful in tests in eight commercial cotton fields. A trap composed of a yellow plastic plate (15 × 20 cm) smeared on the upper side with a thin layer of glue, was attached to an iron pole which held the plate in a horizontal position above the plants. The traps were placed 400 m apart along the periphery of the field. The sticky plates were changed weekly and the adult whiteflies were counted. When the mean weekly catch per trap reached ~ 100–200 adults, spray applications were carried out. Following this treatment,B. tabaci populations remained low and sooty mould did not develop on the lint.  相似文献   
5.
Laparoscopic surgery in adult cattle.   总被引:6,自引:0,他引:6  
Laparoscopy in cattle is a promising tool for clinical diagnosis and treatment. The lower cost of the materials available in addition to the possibility of an intervention on an animal that is sedated does not entail more costs than an exploratory laparotomy. The application of this tool during abdominal explorations and biopsies allows the avoidance of invasive and often useless surgical interventions and even with the diagnosis and prognosis of certain conditions. Surgical techniques currently are limited to abomasopexies; however, never-ceasing progress and improvements in human surgery are expected to affect the future of bovine surgery.With the advancements in the multimedia technology used by universities, the use of laparoscopy as a pedagogic tool definitely has a promising future. Endoscopic exploration of the thorax is possible using the same material as for laparoscopy. In addition, diagnostic and biopsy applications are useful. The use of the laparoscope in different body cavities and for different applications would make the purchase of the required materials more cost-effective.  相似文献   
6.
7.
To better characterise at the molecular level the nature of plant responses to infection by Rhodococcus fascians PCR-based differential display patterns of Atropa belladonna leafy gall (LG) and non-infected plant tissues were compared. Six differentially expressed genes were identified and their altered expression was confirmed by RT-PCR. Three of them corresponded to up-regulated genes which encode proteins involved in plant defence. The three remaining cDNA fragments which correspond to down-regulated genes in LG, encoded proteins with similarity to a multicystatin, a miraculin and a methallothionein-like protein, respectively. Upon elimination of the bacteria from infected plant tissue, the expression of up-regulated genes was maintained, whereas expression of down-regulated genes resumed suggesting a potential role of these up-regulated genes in plant growth and development.  相似文献   
8.
Fish associations with different types of littoral habitats were studied in four canyon‐shaped reservoirs in the Czech Republic in years 2010 and 2011 by gillnets. Two to three habitats per reservoir–beaches (former meadows), stump fields (former forest) and rubble slopes–were defined and sampled along the longitudinal axis of reservoirs. Effects of reservoir, habitat and locality (position along longitudinal axis) on fish biomass, abundance and species structure were tested for juvenile and adult fish separately. Hierarchical analysis of variance revealed that habitats differed significantly in fish biomass and abundance. Redundancy analysis showed that analysed environmental variables had significant influence on fish community structure. Most variability in community structure was explained by reservoir and then by combination of habitat and slope steepness. Locality position had the smallest influence on community structure. For both adult and juvenile fish total abundance and biomass, the most inhabited habitat was beaches; rubble slopes were the least inhabited. Habitat associations differed among species. Among adults, bream Abramis brama, white bream Blicca bjoerkna and roach Rutilus rutilus were associated with beaches and stump fields, whereas perch Perca fluviatilis, ruffe Gymnocephalus cernuus, asp Aspius aspius and pike Esox lucius were associated with rubble slopes. Bream, white bream, bleak Alburnus alburnus, roach, ruffe and pikeperch Sander lucioperca were associated with beaches among juveniles, whereas the only juvenile associated with rubble slopes was perch. We showed that most common species are associated with distinct habitats and also that utilisation of various littoral habitats differs in general.  相似文献   
9.
10.
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