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   524篇
  免费   35篇
林业   30篇
农学   25篇
基础科学   2篇
  95篇
综合类   13篇
农作物   30篇
水产渔业   77篇
畜牧兽医   232篇
园艺   9篇
植物保护   46篇
  2023年   12篇
  2022年   11篇
  2021年   48篇
  2020年   41篇
  2019年   54篇
  2018年   35篇
  2017年   34篇
  2016年   21篇
  2015年   18篇
  2014年   27篇
  2013年   25篇
  2012年   32篇
  2011年   47篇
  2010年   26篇
  2009年   12篇
  2008年   15篇
  2007年   19篇
  2006年   17篇
  2005年   18篇
  2004年   9篇
  2003年   14篇
  2002年   9篇
  2000年   1篇
  1998年   1篇
  1996年   1篇
  1992年   1篇
  1991年   2篇
  1990年   1篇
  1986年   1篇
  1983年   2篇
  1982年   1篇
  1981年   2篇
  1977年   1篇
  1969年   1篇
排序方式: 共有559条查询结果,搜索用时 15 毫秒
531.
The baseflow of tributaries to the Velhas River in the northwest region of Ouro Preto County (São Francisco Basin, Brazil) has been declining in the last years, without a simultaneous decrease in the water input. This can only be attributed to badly planned human activities, which result in soil crusting or compaction, erosion, among other types of impact, such as groundwater overexploitation and wetland drainage. Almost all of the study area has been eroded by hundreds of large-size gullies. In order to analyze the influence of erosion in the hydrological behavior of small streams, two similar and contiguous catchments were selected. The only remarkable difference between them is a gully that occupies circa 42% of one of the catchments (“eroded catchment”). Rainfall, flow rates and chemical data were obtained throughout a hydrological year and the results showed that the eroded catchment presented smaller baseflow rates and bigger but short-lived stormflows. This contrasting flow regime is attributed to the gully, which is causing the partial withdraw of the regolith and the exposure of weathered rock. As the regolith has smaller hydraulic conductivities and higher storage coefficients, the exposure of weathered rock on the gully floor explains the odd flow behavior of the eroded catchment. Other studies in the same region confirm the impact caused by the gullies. Thus, the superposition of many gullies can cause decrease of the baseflow and increase of the stormflow. As gullies are very common erosion features in Brazil, they should be much more studied in order to better understand this and other similar types of environmental impact.  相似文献   
532.
Tropical Animal Health and Production - Communal rearing has been reported in several mammals, including wild ungulates. However, until now, there was no evidence of any alloparental care in the...  相似文献   
533.
Anatomical variation in wild canids is rarely described. Altered shapes, uni- or bilaterally situated, were observed in ventral laminae of C6 and/or in C7 vertebral body of two fox species: Lycalopex gymnocercus and Cerdocyon thous. The specimens were young adults, collected dead on highways in southern Brazil. Deformities were considered anatomical variations because apparently there was no interference in function. The occurrence of such variations in two related species from the same area can suggest an environmental common cause rather than genetic issues. Future studies may deepen the understanding between cause and effect of these vertebral deformities in wild canids.  相似文献   
534.
The white-eared opossum present a higher roadkill number in Brazil, and the vertebral column is often affected when some type of trauma occurs. Thus, this study describes the osteology and radiology of the vertebral column in white-eared opossum to serve as a basis for support in the veterinary clinical care, since the casuistry of care of this marsupial has increased every year. Radiographs of the cervical (C), thoracic (T), lumbar (L), sacral (S) and caudal (Cd) segments of the vertebral column were taken in thirty-five white-eared opossums (Didelphis albiventris). Furthermore, ten opossums without evident vertebral acquired or congenital abnormalities at the radiographic study were selected for anatomical study. Osteology was correlated with the radiographic images. The use of radiographs allowed the identification of congenital and acquired vertebral changes, as well as the identification of anatomical structures, their distribution and morphology and the number of vertebrae. The vertebral formula varied in the white-eared opossum. In 27 of 35 white-eared opossums (77.2%) with normal vertebral morphology, three vertebral formulas were observed: C7/T13/L6/S2 (62.9%), C7/T13/L5/S2 (5.7%) and C7/T13/L7/S2 (8.6%). Most of the specimens presented 27 caudal vertebrae. The anticlinal vertebra was identified as T10 in 77.2% and T11 in 22.8% of opossums. Cervical block vertebra was observed in two animals and sacrocaudal block vertebra in one animal. The haemal arches could be seen from Cd3–Cd4 in 80% and Cd2–Cd3 in 20% of opossums. The white-eared opossum showed a slender vertebral column with a relatively short thoracic region, a relatively long lumbar region and a highly flexible lumbosacral transition, suggesting that this animal is a fast-running and agile opossum. Therefore, these findings may serve as a basis for further research and support the veterinary clinical care, since the casuistry of care for this marsupial has increased every year.  相似文献   
535.
Baseline data for wall thickness in healthy toucans can be used to diagnose disease in sick individuals. This study aimed to evaluate the use of ultrasonography for the examination of the gastrointestinal tract of healthy toco toucans (Ramphastos toco). Ten non-anaesthetized healthy adult toco toucans were evaluated. Food was withheld for 3 h prior to the ultrasound examination. Longitudinal and transverse images of the gastrointestinal tract were obtained using ventromedian cranial and ventromedian caudal approaches to evaluate the morphology and stratification. The wall thickness of the sections was measured: proventriculus and ventriculus, duodenum, jejunum/ileum, and cloaca. Additionally, the thickness of the mucosal layer of the duodenum and jejunum/ileum was also measured. Subsequently, the ratios of the duodenal wall thickness to the duodenal mucosa layer and the total wall thickness of the jejunum/ileum to the jejunum/ileum layer mucosa were stablished. The wall thickness of the proventriculus was significantly higher than the wall thickness of ventriculus. The wall thickness of the duodenum was significantly higher than the wall thickness of jejunum/ileum. The mean ratios of the duodenal wall thickness to the duodenal mucosa layer and the wall thickness of the jejunum/ileum to the jejunum/ileum layer were 83.15% and 80.07%, respectively. In conclusion, it was possible to assess the stomach and intestines using ultrasound examination in healthy toco toucans, due to their medium body size and no interference by surrounding air sacs.  相似文献   
536.
537.
The objective is to evaluate different bedding materials, including dehydrated grass, on performance and carcass yield and verify the physicochemical and microbiological characteristics of materials. The completely randomized experiment comprised 1,080 chicks in a 3 × 2 factorial design with three levels of dehydrated grass (0%, 25%, and 50%) and two bedding materials (rice husks and shavings). Total microorganism count and physicochemical characteristics, surface temperature of birds, and performance of birds were analyzed up to 42 days of age, when birds were slaughtered, and carcass yield was evaluated. The inclusion of grass showed a higher microbiological count after 1 day, stabilizing with materials after 28 days. The inclusion of 50% of dehydrated grass resulted in a higher surface bed temperature at 42 days. Inclusions above 25% of grass have a lower density and a greater water retention capacity, pH, moisture, and total nitrogen, in addition to a lower FDA in its structure. The highest ammonia emissions occurred with the inclusion of 25% of grass. The inclusion of dehydrated grass did not affect performance and carcass yield, favoring feed conversion at the initial stages. The inclusion of grass can replace up to 25% of shavings without harming physicochemical parameters of materials and birds' performance.  相似文献   
538.
ObjectiveTo assess the agreement between an oscillometric device and invasive blood pressure (IBP) measurements in anesthetized healthy adult guinea pigs.Study designProspective experimental study.AnimalsA total of eight adult Hartley guinea pigs.MethodsAll animals were anesthetized; a carotid artery was surgically exposed and catheterized for IBP measurements. A size 1 cuff placed on the right thoracic limb was connected to an oscillometric device for noninvasive blood pressure (NIBP) assessment. Concurrent pairs of systolic (SAP), diastolic (DAP) and mean (MAP) arterial pressures were recorded simultaneously with both methods every 3 minutes for 30 minutes. Agreement between IBP and NIBP measurements was determined using the Bland–Altman method, considering the recommended standards for the validation of NIBP measurement devices proposed by the American College of Veterinary Internal Medicine (ACVIM).ResultsThe bias and the 95% limits of agreement were: –14 (–31 to 3) mmHg, –2 (–14 to 10) mmHg and –1 (–13 to 11) mmHg for SAP, DAP and MAP, respectively.Conclusions and clinical relevanceThe oscillometric device used in this study to measure NIBP did not meet ACVIM criteria for validation. It showed good agreement for DAP and MAP but not for SAP measurements. Considering the small size of these animals and the resulting difficulty in performing percutaneous arterial catheterization, this device might be a useful tool to assess MAP and DAP during anesthetic procedures in adult guinea pigs.  相似文献   
539.
Mesotheliomas are uncommon neoplasms that arise from mesothelial cells in either the abdominal or thoracic cavities and are rarely diagnosed in cats. A 10-y-old spayed female domestic shorthair cat was presented to the Louisiana State University oncology service for evaluation of a large amount of abdominal effusion. Abdominal ultrasound identified a large mesenteric mass with numerous ill-defined nodules. An abdominocentesis was performed with cytologic and immunocytochemical findings consistent with a neoplastic effusion, with large clusters of epithelioid cells that exhibited strong cytoplasmic expression of pancytokeratin, vimentin, and Wilms tumor 1 antigens. Further testing was declined, and meloxicam was prescribed until the cat died 23 d after initial presentation. Upon postmortem examination, the omentum was contracted into a firm mass adhered to multiple organs and accompanied by numerous small white nodules throughout the abdominal cavity. On histopathology and immunohistochemistry, neoplastic cells were found throughout the abdominal cavity; 60–95% exhibited moderate-to-strong cytoplasmic immunoreactivity for cytokeratin, vimentin, and Wilms tumor 1 protein. The final diagnosis was an epithelioid mesothelioma. Our case illustrates the utility of cytology, immunocytochemistry, and its relation to histology and immunohistochemistry. We also reviewed the reported cases of feline mesothelioma.  相似文献   
540.
The strong odour of faeces and excessive production of gases in some dog breeds have long been a concern of owners. The pet food industry uses nutritional alternatives, such as high-quality ingredients and additives, to improve the odour of faeces. However, there are still some dog breeds, such as the French Bulldog, that present this problem due to the presence into the large intestine of indigested protein. Therefore, a deeper understanding of the volatile compounds that influence the odour of dog faeces is important. This study aimed to identify changes of faecal odour compounds that are most prevalent in French Bulldogs based on food containing different high-quality protein sources and their effect in sensory analysis. Four maintenance foods with different protein sources were formulated: P, poultry meal food; W, wheat gluten food; PW, poultry meal and wheat gluten food; and PWH, poultry meal, wheat gluten, and hydrolysed protein food. Eight adult French Bulldogs were arranged in a 4x4 Latin square design and adapted to foods for 28 days. Fresh faeces were collected for analysis of volatile organic compounds (VOCs) and sensory analysis. The means were compared by SAS, and statistical significance was indicated by ≤ 0.05. No adverse effects were observed in the animals regarding VOCs, and a significant difference was observed in two of the 68 compounds identified. The animals fed a P food had higher concentrations of phenol in the faeces, whereas the indole compound was present at higher concentrations in animals fed the W food. P food was associated with higher odour perception during sensory evaluation. In summary, the source of protein in the foods had little impact on the composition of VOCs, and a greater perception of the odour was determined by sensory analysis when foods containing animal protein were administered.  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