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   547篇
  免费   21篇
林业   25篇
农学   10篇
基础科学   1篇
  115篇
综合类   55篇
农作物   15篇
水产渔业   30篇
畜牧兽医   272篇
园艺   10篇
植物保护   35篇
  2023年   3篇
  2021年   4篇
  2020年   9篇
  2019年   11篇
  2018年   10篇
  2017年   8篇
  2016年   10篇
  2015年   9篇
  2014年   19篇
  2013年   35篇
  2012年   22篇
  2011年   43篇
  2010年   15篇
  2009年   17篇
  2008年   37篇
  2007年   29篇
  2006年   27篇
  2005年   26篇
  2004年   32篇
  2003年   20篇
  2002年   20篇
  2001年   11篇
  2000年   12篇
  1999年   11篇
  1998年   4篇
  1995年   5篇
  1994年   3篇
  1993年   3篇
  1992年   9篇
  1991年   6篇
  1990年   3篇
  1989年   6篇
  1988年   6篇
  1985年   5篇
  1984年   3篇
  1983年   4篇
  1982年   4篇
  1980年   4篇
  1979年   3篇
  1978年   5篇
  1977年   2篇
  1976年   2篇
  1974年   5篇
  1973年   3篇
  1972年   4篇
  1971年   2篇
  1970年   6篇
  1969年   2篇
  1966年   2篇
  1961年   3篇
排序方式: 共有568条查询结果,搜索用时 218 毫秒
1.
Neutrophils were isolated from the blood of pregnant cows on days 255, 265, and 275 of pregnancy, and on the day of parturition (n = 5/group), and in addition, simultaneously from 4 ovariectomized healthy cows (control animals). Neutrophils were subjected to neutrophil function assays (chemotaxis against zymosan-activated serum, random migration, ingestion of 125I-iododeoxyuridine [IdUR]-labeled Staphylococcus aureus, iodination of proteins, cytochrome C reduction, antibody-independent and antibody-dependent cell-mediated cytotoxicity). Results were expressed as percentage of control animals. Fetal placental tissue (cotyledon), uterine wall tissue, and skeletal muscle were obtained from the principal animals on the aforementioned days via laparotomy, and tissue suspensions were prepared. Chemotaxis of neutrophils was tested against tissue supernatants. Compared with day 255, there was an increase in ingestion of 125I-IdUR-S aureus at parturition, whereas iodination of proteins and cytochrome C reduction were reduced on the day of calving. The other neutrophil functions tested did not change over time of gestation. Fetal placental and uterine wall tissue attracted neutrophils with uterine wall tissue having a tendency to be more potent than cotyledonary tissue. Skeletal muscle tissue did not attract neutrophils. There was no change in chemotaxis response of neutrophils evoked by intrauterine and uterine tissues over time of gestation. It was concluded that at parturition, neutrophil function is impaired with respect to their bactericidal effects, which may render the animal more susceptible to bacterial infections, and that the chemoattractant properties of fetal placental and uterine wall tissues are tissue-specific, at least when compared with skeletal muscle.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
2.
This study assessed the ranking of dairy cows using individual-level correlations for methane (CH4) emission on-farm using sniffers and in respiration chambers. In total 20 lactating dairy cows, ten Holstein and ten Jerseys were recorded using sniffers installed in milking robots for three weeks of lactation and subsequently in respiration chambers (RC) where they were each recorded on three occasions within the RC. Bivariate linear mixed models were used to determine the individual-level correlations (rI) between sniffer and RC phenotypes as proxies for genetic correlations. Despite differences in feeding and management, the predicted CH4 production from sniffers correlated highly with RC CH4 production rI?=?0.77?±?0.18 and CH4 breath concentration correlated nearly as well with RC CH4 production rI?=?0.75?±?0.20. These correlations between sniffers on-farm and RC demonstrate the potential of sniffers measurements as large-scale indicator traits for CH4 emissions in dairy cattle.  相似文献   
3.
4.
5.
This article describes the Finnish meat-inspection curriculum and presents an expert-panel evaluation of meat-inspection education. The work tasks of the meat-inspection veterinarian are challenging and include classical meat inspection, meat hygiene, hygiene control, and animal disease and welfare. The meat-inspection veterinarian is not only an inspector, which by itself is very demanding, but also an expert or "consultant" on food safety. The significant role of the meat-inspection veterinarian in society puts high demands on meat-inspection education, which should provide veterinary students with sufficient tools to perform meat inspection and hygiene control in slaughterhouses, cutting premises, and further processing plants. To be of high quality, such education must be evaluated from time to time. An expert panel evaluated Finnish undergraduate meat-inspection education and found that it provides veterinary students with good knowledge of meat inspection. The structure of the curriculum, with theoretical studies followed by four weeks of practice in a slaughterhouse, was considered vital for learning and for creating interest in meat inspection. The evaluation also revealed that certain subjects should receive greater emphasis and some new subjects should be introduced. Hygiene-control tasks, in particular, have increased and should receive more emphasis in education. Personnel management and interaction skills should be introduced into the curriculum as these skills influence all the duties of the meat-inspection veterinarian. This article outlines the subjects to be included in the modern, high-quality meat-inspection curriculum recommended by the expert panel.  相似文献   
6.
Myxoma virus (MV) is a poxvirus that evolved in Sylvilagus lagomorphs, and is the causative agent of myxomatosis in European rabbits (Oryctolagus cuniculus). This virus is not a natural pathogen of O. cuniculus, yet is able to subvert the host rabbit immune system defenses and cause a highly lethal systemic infection. The interaction of MV proteins and the rabbit immune system has been an ideal model to help elucidate host/poxvirus interactions, and has led to a greater understanding of how other poxvirus pathogens are able to cause disease in their respective hosts. This review will examine how MV causes myxomatosis, by examining a selection of the identified immunomodulatory proteins that this virus expresses to subvert the immune and inflammatory pathways of infected rabbit hosts.  相似文献   
7.
The diversity of fungal endophytes in Sorghum bicolor was investigated in samples collected from 10 different geographical regions of Karnataka state, India. A total of 360 endophytes were isolated from leaf, stem, and root tissues and were assigned to 26 fungal species based on morphology and molecular characterization using ITS sequences. All the endophytes belonged to the phylum Ascomycota. The diversity (Shannon H, 2.57; Simpson_1-D, 0.92) and species richness (Margalef's, 4.68; Menhinick, 3.61) were found to be higher for the endophytes isolated from leaf tissues. The species evenness of the endophytic assemblage was strongly influenced by tissue type, followed by geographical location. The biocontrol potential of isolated endophytes was evaluated against economically destructive sorghum grain mould pathogens such as Fusarium thapsinum, Epicoccum sorghinum, Alternaria alternata, and Curvularia lunata using the dual culture method. Biocontrol potential was exhibited by 26 endophytic isolates, of which Trichoderma asperellum recorded broad-spectrum activity against target pathogens, followed by E. nigrum and A. longipes. Most (82%) endophytes showed plant growth-promoting traits. Biosynthesis of indole-3-acetic acid (IAA) was observed in 84% of isolates, and phosphate solubilization, siderophore production, and cellulase activity was observed in 69%, 23%, and 27% of isolates, respectively. Seeds treated with Tasperellum exhibited a significantly higher seed vigour index (2096), germination percentage (94%), and yield under greenhouse and field conditions. The results were substantiated by the confocal microscopy analysis, which clearly demonstrated the colonization of treated endophyte in root tissues. The present study reveals an ecofriendly approach to explore Tasperellum in sorghum disease management.  相似文献   
8.
A 9‐wk study was conducted to evaluate the effect of dietary protein and energy on growth performance of juvenile permit, Trachinotus falcatus, growing from approximately 30 to 150 g. Nine experimental diets were formulated to contain three levels of crude protein (400, 450, and 500 g/kg dry matter [DM]); and three levels of crude lipid (100, 200, and 300 g/kg DM) in a 3 × 3 factorial design. Growth rate and feed efficiency were significantly improved with increasing dietary protein levels from 400 to 500 g/kg and with dietary lipid levels from 100 to 200 g/kg. Fish body protein content was positively correlated with dietary ratio of digestible protein (DP) to digestible energy (DE) (P < 0.01, R2 = 0.83), while body lipid was negatively correlated with dietary DP/DE (R2 = 0.55, P < 0.05) but positively correlated with dietary DE levels (R2 = 0.66, P < 0.01). Results showed a protein‐sparing effect, as protein retention was significantly increased by increasing dietary lipid level. In conclusion, the diet containing DP of 392.7 g/kg and DE of 18.8 MJ/kg (DM), corresponding to a DP/DE of 20.9 g/MJ, is suggested as an optimal feed for growth and feed efficiency in juvenile permit.  相似文献   
9.

Context

The ability to detect ecological networks in landscapes is of utmost importance for managing biodiversity and planning corridors.

Objectives

The objective of this study was to evaluate the information provided by a synthetic aperture radar (SAR) image for landscape connectivity modeling compared to aerial photographs (APs).

Methods

We present a novel method that integrates habitat suitability derived from remote sensing imagery into a connectivity model to explain species abundance. More precisely, we compared how two resistance maps constructed using landscape and/or local metrics derived from AP or SAR imagery yield different connectivity values (based on graph theory), considering hedgerow networks and forest carabid beetle species as a model.

Results

We found that resistance maps using landscape and local metrics derived from SAR imagery improve landscape connectivity measures. The SAR model is the most informative, explaining 58% of the variance in forest carabid beetle abundance. This model calculates resistance values associated with homogeneous patches within hedgerows according to their suitability (canopy cover density and landscape grain) for the model species.

Conclusions

Our approach combines two important methods in landscape ecology: the construction of resistance maps and the use of buffers around sampling points to determine the importance of landscape factors. This study was carried out through an interdisciplinary approach involving remote sensing scientists and landscape ecologists. This study is a step forward in developing landscape metrics from satellites to monitor biodiversity.
  相似文献   
10.
We describe the abnormal magnetic resonance (MR) imaging findings in the deep digital flexor tendon (DDFT) and distal sesamoid bone in horses with radiographic changes compatible with navicular syndrome. Thirteen postmortem specimens were examined using a 1.5-T magnetic field, with spin echo (SE) T1-weighted, turbo SE (TSE) proton density-weighted (with and without fat saturation), and fat saturation TSE T2-weighted sequences. The limbs were then dissected to compare the MR findings with the gross assessment and histologic examination of the DDFT and distal sesamoid bones. Tendonous abnormalities were detected by MR imaging in 12 DDFTs and confirmed at necropsy. Most tendon lesions were located at the level of the distal sesamoid bone and the proximal recess of the podotrochlear bursa. Tendon lesions were classified based on their MR imaging features as core lesions, dorsal lesions, dorsal abrasions, and parasagittal splits. Areas of increased MR signal in the DDFTs were characterized by tendon fiber disturbance and lack of continuity of the collagen fibers, foci of edema, hemorrhages, and formation of lakes containing eosinophilic plasma-like material or amphophilic material of low density. Bone marrow signal alterations in the distal sesamoid bone were seen in all digits. Two main phenomena were responsible for the abnormal signal, respectively, in T1-weighted (decreased signal) and in T2-weighted fat-suppressed images (increased signal): a decrease in the fat marrow content in the trabecular spaces and an increase in the fluid content. Histologic examination revealed foci of bone marrow edema, hemorrhage, necrosis, and fibrosis. Cyst formation and trabecular abnormalities (disorganization, thinning, remodelling) were also observed in areas of abnormal signal intensity. Increased bone density because of trabecular thickening induced a decrease in signal in all sequences.  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