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   963篇
  免费   88篇
  国内免费   1篇
林业   62篇
农学   38篇
基础科学   5篇
  184篇
综合类   54篇
农作物   76篇
水产渔业   120篇
畜牧兽医   403篇
园艺   16篇
植物保护   94篇
  2023年   4篇
  2022年   9篇
  2021年   10篇
  2020年   28篇
  2019年   27篇
  2018年   34篇
  2017年   46篇
  2016年   37篇
  2015年   38篇
  2014年   52篇
  2013年   58篇
  2012年   62篇
  2011年   45篇
  2010年   46篇
  2009年   39篇
  2008年   59篇
  2007年   42篇
  2006年   44篇
  2005年   39篇
  2004年   32篇
  2003年   28篇
  2002年   21篇
  2001年   24篇
  2000年   23篇
  1999年   18篇
  1998年   25篇
  1997年   20篇
  1996年   18篇
  1995年   20篇
  1994年   10篇
  1993年   5篇
  1992年   10篇
  1991年   9篇
  1990年   8篇
  1989年   10篇
  1988年   3篇
  1987年   6篇
  1986年   2篇
  1985年   5篇
  1984年   3篇
  1982年   2篇
  1981年   2篇
  1980年   7篇
  1979年   3篇
  1975年   2篇
  1974年   2篇
  1972年   2篇
  1971年   3篇
  1961年   2篇
  1944年   1篇
排序方式: 共有1052条查询结果,搜索用时 15 毫秒
91.
Objective To review the breed, age, gender, clinical and laboratory findings, treatment and outcome of horses with caecal disease presented to a referral centre. Design Retrospective study of 96 cases. Procedure The breed, age, and gender of the study population were compared with the corresponding hospital population for the same period. The means (± SD) for clinical and laboratory findings were recorded for each caecal disorder. Treatment was categorised as medical or surgical, and outcome was recorded. Results Caecal diseases included impaction (40% of total cases), rupture associated with concurrent unrelated disease (13%), rupture with parturition (9%), rupture with no associated disease (5%), infarction (11%), torsion (9%), abscess or adhesion (7%), tumour (3%), and miscellaneous conditions (3%). The breed or gender of affected horses did not differ from the hospital population, although horses > 15 years were more frequently represented (P < 0.05). This age group was specifically more predisposed to caecal impaction (P < 0.05), as were Arabian, Morgan, and Appaloosa breeds (P < 0.05). In horses with caecal impaction transrectal examination was the most useful diagnostic procedure; 90% of affected horses treated medically were discharged while horses treated by typhlotomy alone, or typhlotomy and blind end ileocolostomy, had survival rates to discharge of 71% and 86%, respectively. Horses with caecal rupture associated with concurrent un-related disease showed no signs of impending rupture; all were receiving phenylbutazone, all were euthanased, and 50% had caecal ulceration at necropsy. Of horses with caecal rupture with parturition 56% had prior dystocia; in two-thirds the site of rupture was the ileocaecal junction and all were euthanased. Horses with caecal rupture with no associated disease died or were euthanased; rupture was idiopathic. Horses with caecal infarction usually had signs of abdominal pain and abdominal fluid changes consistent with peritonitis; transrectal examination was nonspecific, and typhlectomy was successful in seven of eight horses. Horses with caecal torsion had signs of severe, acute abdominal pain and typhlectomy was successful in three of five horses. Diagnosis of caecal adhesion or abscess was assisted by transrectal palpation in two of seven horses and surgical treatment was successful in two of five horses. A caecal tumour was diagnosed in three horses aged 20 years or older that presented with chronic weight loss. Other caecal diseases were uncommon. Conclusion Caecal disease is uncommon in equids but some specific features of the history and physical findings can alert the veterinarian to the possibility of caecal involvement in horses with gastrointestinal dysfunction. Medical or surgical therapy can be effective in horses where caecal rupture has not occurred.  相似文献   
92.
In order to develop a general model of aboveground net primary production (ANPP) of herbaceous communities in grazing systems that combine forested and open grasslands in temperate areas, biomass production and a set of biotic and abiotic variables were measured at four adjacent forest and grassland sites in Chile’s northern Patagonia for two consecutive growing seasons. At each site, one transect of 80 m long (40 m in open grassland and 40 m in forest) × 10 m wide was established. ANPP was significantly higher in open grasslands but no gradual change in biomass production was observed from inside the forest towards the open grassland. In open grasslands ANPP was spatially uniform but highly variable between years of contrasting weather conditions, whereas in forests it was more spatially heterogeneous and less variable over time. ANPP was highly correlated with cattle consumption. Structural equation models developed for the whole system confirm that ANPP was driven mainly by photosynthetically active radiation (PAR) and available nitrogen. However, we found important differences between forests and the adjacent open grasslands. In forests ANPP was enhanced by positive feedbacks between the amount of transmitted PAR through the canopy and soil nutrient input via cattle dung deposition. In open grasslands nitrogen availability appeared to be the main limiting factor but also influenced by weather conditions (dryer or wetter years). The coexistence of forests and grasslands patches, with different susceptibility of ANPP to meteorological and soil nutrient availability, highlights the importance of implementing an integrated silvopastoral system with lenga (Nothofagus pumilio [Poepp. & Endl.] Krasser) in northern Patagonia.  相似文献   
93.
The Syrian hamster (Mesocricetus auratus) is the best animal model for human leishmaniosis, an emergent disease that causes 400,000 new cases every year. The main objective of this assay was to prove the relationship between female lactation, which implies hyperprolactinaemia (IFN-gamma, IL-12, IL-2 and TNF-alpha elevated), and leishmaniosis (IFN-gamma, IL-12, IL-2 and TNF-alpha diminished). The results demonstrate the clear implication of lactation in immune response. The infected lactating females did not show any symptoms of sickness, a 24 g mean increase was noticed, throughout the assay they were negative in the indirect diagnosis test (Direct Agglutination Test (DAT)), and in the direct diagnosis tests (N-N-N isolation, tissue impressions).  相似文献   
94.
1. A trial was conducted in order to increase the docosahexaenoic acid (DHA) content in the meat of Muscovy ducks (Cairina moschata domestica L.) fed on a diet supplemented with the microalga Crypthecodinium cohnii. 2. Two diets were provided to 48 male and 48 female ducks, belonging to an Italian rural strain during the last 3 weeks of life: a maize-soybean based diet as the control diet and the same diet supplemented with 5 g/kg microalga meal. 3. Dietary treatment did not induce differences in growth performances and slaughter traits. Similarly, chemical composition, colour, pH, oxidative stability and sensory characteristics of breast muscle were not influenced by the diet. 4. A significant increase of DHA content in breast meat of ducks fed on the Crypthecodinium cohnii enriched diet was observed.  相似文献   
95.
A diagnosis of dicoumarol toxicity in a herd of Friesian cattle was made following investigation of the deaths of three mature cows and eleven yearling heifers. Affected stock had been fed wrapped, bailed silage containing approximately 90% sweet vernal grass ( Anthoxanthum odoratum ). Sweet vernal grass contains coumarin, which can be converted to dicoumarol, a vitamin K antagonist, through the action of moulds. Most deaths were preceded by lethargy, severe anaemia and subcutaneous and internal haemorrhage. Dicoumarol toxicosis was suspected based on clinical signs, necropsy findings and prolonged prothrombin and activated partial thromboplastin times. Dicoumarol analysis of blood from affected animals and silage confirmed the diagnosis.  相似文献   
96.
97.
To determine the relationship between first service conception rate (FSC) and the postpartum period (PP), 6160 calvings from 2250 crossbred dual-purpose cows were analysed. The effects of breed predominance (BT: Bos taurus and BI: Bos indicus), season of service (dry, intermediate and humid), parity (1 or 2 and more), agroecological region (Sub-humid and Dry Tropical Forest) and milk production were studied. The postpartum period was grouped according to the calving–first service interval as G1 ≤ 60 days (n = 1889); G2 > 60 ≤ 90 days (n = 1436); G3 > 90 ≤ 120 days (n = 1030); and G4 > 120 days (n = 1805). Data were analysed by chi-squared test. The overall mean for FSC was 58.2% and was lower in G1 (p < 0.01). All PP showed a breed effect on FSC, with mean values of 61.6% and 53.3% for BI and BT, respectively. Season of service also affected FSC, which was significantly lower during the humid period: 51.2% versus 57.4% and 61.5% for the intermediate and dry periods (p < 0.01), respectively. Parity and environmental effects were not observed on FSC. Levels of milk yield did influence the FSC, which decreased from 66.7% and 61.0% for milk yields of < 1500 kg and between 1501 and 2000 kg to 46.0% in milk yields > 2000 kg (p < 0.01).  相似文献   
98.
The efficacy of specific immunochemotherapy against Leishmania infantum infection in dog was studied. The effects on transmission of the disease, as well as the cellular and humoral immune response were examined. The treated animals showed a significant reduction in the infection rates that were detected in Phlebotomus perniciosus females fed on the dog. The humoral immune response, assayed with an indirect immunofluorescence antibody test (IFAT), did not show significant variations under the influence of the therapy. The characterisation of the peripheral blood mononuclear cells (PBMC) using flow cytometry indicated a significant increase in the proportion of T lymphocytes, especially of CD4/TcR(alpha)(beta)(+) and CD4/CD45RA(+) cells, without showing evidence for modifications in the other leukocyte subsets. Cellular lymphoproliferation studies indicated a lack of a specific response to soluble leishmanial antigen (SLA), but the non-specific lymphoproliferative capacity assayed with phytohemagglutinin (PHA) was maintained.  相似文献   
99.
Genetic variation in ratoon growth and cane yieldafter mechanical harvesting under wet conditions wasexamined among 26 sugarcane clones of diverse geneticbackground, including materials closely related toSaccharum spontaneum and some commercialcultivars. The clones were evaluated under a controltreatment (harvesting under dry conditions andallowing the cane to ratoon without furtherdisturbance), and a traffic treatment (sprayirrigation and then driving heavy field equipment overthe cane stubble immediately after harvesting). Averaged over all clones, the traffic treatment had alarge adverse effect on early growth and final ratoonyield. There was significant genotype × treatmentinteraction for early growth and canopy development,but not for final cane yield. There was also a highgenetic correlation between genetic performance underthe different treatments, indicating that selectionfor ratooning after dry harvesting conditions would bealso effective for improving performance after wetharvesting conditions. A sugarcane breeding programspecifically targeting better ratoon performance underwet conditions would be difficult to justify.  相似文献   
100.
Internal migration has been recognized as the major influence in terms of population redistribution across urban systems, but it is not a homogeneous phenomenon. Within the context of internal rural‐urban migration decline and the negative changes in migratory balances in the metropolitan area of Mexico City, the core of enquiry in this paper is the approach to growth and consolidation of an internal urban–urban migration system in the early twenty‐first century (2000–2015). This process has taken place through two main networks, among metropolitan areas not corresponding to the principal city and among intermediate cities. Internal migration is a complex process that involves both individual and spatial characteristics and which leads to spatially uneven development in the long term. Data from three censuses of the population of Mexico (2000, 2010, and 2015) show a transition to a more urban–urban migration pattern, with skilled migrants tending to have metropolitan and urban destinations, whereas less‐skilled migrants prefer rural and small urban destinations.  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