全文获取类型
收费全文 | 544篇 |
免费 | 24篇 |
专业分类
林业 | 22篇 |
农学 | 9篇 |
77篇 | |
综合类 | 56篇 |
农作物 | 35篇 |
水产渔业 | 24篇 |
畜牧兽医 | 292篇 |
园艺 | 23篇 |
植物保护 | 30篇 |
出版年
2023年 | 4篇 |
2022年 | 3篇 |
2021年 | 9篇 |
2020年 | 12篇 |
2019年 | 15篇 |
2018年 | 11篇 |
2017年 | 5篇 |
2016年 | 12篇 |
2015年 | 14篇 |
2014年 | 11篇 |
2013年 | 28篇 |
2012年 | 28篇 |
2011年 | 29篇 |
2010年 | 10篇 |
2009年 | 22篇 |
2008年 | 36篇 |
2007年 | 30篇 |
2006年 | 38篇 |
2005年 | 51篇 |
2004年 | 38篇 |
2003年 | 36篇 |
2002年 | 37篇 |
2001年 | 7篇 |
2000年 | 3篇 |
1999年 | 7篇 |
1998年 | 3篇 |
1997年 | 7篇 |
1996年 | 7篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1972年 | 1篇 |
排序方式: 共有568条查询结果,搜索用时 15 毫秒
131.
Foley JE Norris CR Jang SS 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2002,16(3):238-243
We reviewed 14 cases of paecilomycosis in a tertiary care veterinary hospital and all reports of the disease in the veterinary literature. Paecilomycosis is a rare disease primarily of dogs, horses, reptiles, and humans. Clinical manifestations in veterinary patients vary but include disseminated disease and diskospondylitis, particularly in dogs: pneumonia in dogs, horses, and reptiles; keratitis in horses; and miscellaneous local infections. It is important to have an appropriate index of suspicion because the diagnosis can be difficult, particularly in localized disease where it is difficult to determine whether a positive culture represents an etiology or a contamination with an environmental saprophyte. Spinal radiographs, transtracheal washes, histopathology, and fungal culture have proven to be valuable diagnostic tools. The prognosis for paecilomycosis is poor, although some treatment success has been reported, and success rates could improve if additional information were available regarding fungal species occurring in veterinary patients and drugs to which these fungi are susceptible. 相似文献
132.
Aric P Krogstad Janet E Simpson Scott W Korte 《Veterinary Clinics of North America: Exotic Animal Practice》2005,8(1):123-138
Viral disease in the rabbit is encountered infrequently by the clinical practitioner; however, several viral diseases were reported to occur in this species. Viral diseases that are described in the rabbit primarily may affect the integument, gastrointestinal tract or, central nervous system or maybe multi-systemic in nature. Rabbit viral diseases range from oral papillomatosis, with benign clinical signs, to rabbit hemorrhagic disease and myxomatosis, which may result in significant clinical disease and mortality. The wild rabbit may serve as a reservoir for disease transmission for many of these viral agents. In general, treatment of viral disease in the rabbit is supportive in nature. 相似文献
133.
Janet Aldrich 《Veterinary Clinics of North America: Small Animal Practice》2005,35(2):281-305
The approach to the global assessment of the emergency patient must bean organized, focused, and efficient pursuit of identification all the patient's problems in the order of their importance to survival. The format of the problem-oriented approach serves as a guide. The patient's history and physical examination results serve as the database for global assessment;they are the core of emergency practice. 相似文献
134.
135.
Olsoy Peter J. Forbey Jennifer S. Shipley Lisa A. Rachlow Janet L. Robb Brecken C. Nobler Jordan D. Thornton Daniel H. 《Landscape Ecology》2020,35(4):921-936
Landscape Ecology - The amount and composition of phytochemicals in forage plants influences habitat quality for wild herbivores. However, evaluating forage quality at fine resolutions across broad... 相似文献
136.
Tomáš Václavík Alan Kanaskie Everett M. Hansen Janet L. Ohmann Ross K. Meentemeyer 《Forest Ecology and Management》2010
An isolated outbreak of the emerging forest disease sudden oak death was discovered in Oregon forests in 2001. Despite considerable control efforts, disease continues to spread from the introduction site due to slow and incomplete detection and eradication. Annual field surveys and laboratory tests between 2001 and 2009 confirmed a total of 802 infested locations. Here, we apply two invasive species distribution models (iSDMs) of sudden oak death establishment and spread risk to target early detection and control further disease spread in Oregon forests. The goal was to develop (1) a model of potential distribution that estimates the level and spatial variability of disease establishment and spread risk for western Oregon, and (2) a model of actual distribution that quantifies the relative likelihood of current invasion in the quarantine area. Our predictions were based on four groups of primary parameters that vary in space and time: climate conditions, topographical factors, abundance and susceptibility of host vegetation, and dispersal pressure. First, we used multi-criteria evaluation to identify large-scale areas at potential risk of infection. We mapped and ranked host abundance and susceptibility using geospatial vegetation data developed with gradient nearest neighbor imputation. The host vegetation and climate variables were parameterized in accordance to their epidemiological importance and the final appraisal scores were summarized by month to represent a cumulative spread risk index, standardized as five categories from very low to very high risk. Second, using the field data for calibration we applied the machine-learning method, maximum entropy, to predict the actual distribution of the sudden oak death epidemic. The dispersal pressure incorporated in the statistical model estimates the force of invasion at all susceptible locations, allowing us to quantify the relative likelihood of current disease incidence rather than its potential distribution. Our predictions show that 65 km2 of forested land was invaded by 2009, but further disease spread threatens more than 2100 km2 of forests across the western region of Oregon (very high and high risk). Areas at greatest risk of disease spread are concentrated in the southwest region of Oregon where the highest densities of susceptible host species exist. This research identifies high priority locations for early detection and invasion control and illustrates how iSDMs can be used to analyze the actual versus potential distribution of emerging infectious disease in a complex, heterogeneous ecosystem. 相似文献
137.
This study was designed to determine if judicious use of synoptic data and an operational trajectory model could identify probable source regions of anthropogenic pollutants in northeastern United States precipitation and thus relate receptor measurements to emissions data without consideration of the complex intervening meteorological and chemical processes. The storm event of April 8 to 10, 1979, was selected for intensive study. Precipitation chemistry data were obtained from event samples at six MAP3S sampling sites and from hourly samples at Brookhaven National Laboratory. Concentrations of hydrogen, sulfate, nitrate and ammonium ions were used as receptor data. Some emissions data for SOx and NOx were obtained from the MAP3S emissions inventory. Surface and upper air meteorological data were analyzed. Backward trajectories ending at each of the sampling sites during the precipitation period were computed with the Heffter Interactive-Terminal Transport Model using selected transport layers. Results show that concentrations of pollutant species in event precipitation samples were much higher at stations at end points of trajectories passing through the Ohio River valley than at stations with other trajectories. Likewise, concentrations at Brookhaven were much higher during the end period of a trajectory through the same region than with more northerly and more southerly tracks. The model produced back trajectories consistent with synoptic flows. Concentrations of air pollutants in precipitation were roughly proportional to the number of major pollutant sources along the trajectory. These results suggest that a larger number of studies might identify more restricted source areas or even establish a quantitative relationship between source emissions along a trajectory and concentrations in precipitation at receptor sites. 相似文献
138.
Light effects on the growth and morphogenesis of potato(Solanum tuberosum) in vitro: A review 总被引:1,自引:0,他引:1
Janet E. A. Seabrook 《American Journal of Potato Research》2005,82(5):353-367
Growth, morphogenesis, and tuberization of potato tissuesin vitro are affected by light. Measurements of the various aspects of light that control development and growth of potato are outlined. Physical parameters like light sources, delivery of the light source, and the degradation of culture media by light are discussed. Irradiance, photoautotrophic growthin vitro, spectral wavelength, and photoperiod modify the responses of potato tissues in culture. Acclimatization of tissue culture plantlets, vegetative growth, and the production, quality, and dormancy of microtubers are modified by light. New light sources such as light-emitting diode (LED) lamps are becoming available forin vitro research and for micropropagation of potato. Pulsed or chopper light has the potential to save energy costs. Light effects on potato protoplasts, anther culture, virus eradication, andin vitro conservation are discussed. Potential new research areas are the effect of the spectral quality of light on regeneration of shoots and somatic embryosin vitro, end-of-day red and far-red light treatments, axillary shoot formation in cultured plantlets, and the use of LEDs. The influence of monochromatic spectral filters on growth and development of potatoes in tissue culture could potentially lead to improvements in productivity. The relationship between daily quantum light integral and photoperiod and their effects on growth and morphogenesis of the potato will provide some useful areas of research. 相似文献
139.
Janet E. A. Seabrook Jane E. Percy L. Katheryn Douglass George C. C. Tai 《American Journal of Potato Research》1995,72(6):365-373
In vitro potato plantlets of cultivar (cv.) Shepody (Solatium tuberosum L.) were exposed to 12-or 16-hr photoperiods for 8 weeks. Plantlets were acclimatized to the greenhouse and grown under 14-hr photoperiods until they senesced, and minitubers were harvested. Greenhouse-grown potato plants developed from tissue-culture plantlets exposed to a 16-hr photoperiod were taller and had more nodes than plants developed from plantlets exposed to 12-hr photoperiods. However, yield data of minitubers from greenhousegrown plants indicated that the 12-hr photoperiodic treatment increased the numbers, dry weight and specific gravity of minitubers. A further advantage of the 12-hr photoperiodic treatment was the greater numbers of minitubers in the 15–40 g size class compared with tubers in the <15 g and >40 g size classes. Thus, for the cv. Shepody, plant height and node number of greenhouse-grown plants were not good indicators of minituber yield from that crop. Seed potato nuclear stock facilities producing minitubers should investigate the possibility of optimizing minituber production by exposing multiplication cultures to shorter daylengths. 相似文献
140.
The effects of future urban development on habitat fragmentation in the Santa Monica Mountains 总被引:8,自引:0,他引:8
A site suitability model of urban development was created for the Santa Monica Mountains in southern California, USA, to project to what degree future development might fragment the natural habitat. The purpose was to help prioritize land acquisition for the Santa Monica Mountains National Recreation Area and examine to what extent projected urban development would affect distinct vegetation classes. The model included both environmental constraints (slope angle), and spatial factors related to urban planning (proximity to roads and existing development, proposed development, and areas zoned for development). It implemented a stochastic component; areas projected to have high development potential in the suitability model were randomly selected for development. Ownership tracts were used as the spatial unit of development in order to give the model spatial realism and not arbitrarily `develop' grid cells. Using different assumptions and parameters, the model projected the pattern of development from 5 to 25 years hence (based on recent development rates in the area). While <25% of the remaining natural landscape is removed under these scenarios, up to 30% of core (interior) habitat area is lost and edge length between natural vegetation and development increases as much as 45%. Measures of landscape shape complexity increased with area developed and number of patches of natural habitat increased four- to nine-fold, depending upon model parameters. This increase in fragmentation occurs because of the existing patterns of land ownership, where private (`developable') land is interspersed with preserved park lands. 相似文献