全文获取类型
| 收费全文 | 609篇 |
| 免费 | 51篇 |
专业分类
| 林业 | 40篇 |
| 农学 | 6篇 |
| 基础科学 | 2篇 |
| 90篇 | |
| 综合类 | 36篇 |
| 农作物 | 22篇 |
| 水产渔业 | 38篇 |
| 畜牧兽医 | 343篇 |
| 园艺 | 6篇 |
| 植物保护 | 77篇 |
出版年
| 2023年 | 6篇 |
| 2022年 | 5篇 |
| 2021年 | 24篇 |
| 2020年 | 24篇 |
| 2019年 | 20篇 |
| 2018年 | 16篇 |
| 2017年 | 18篇 |
| 2016年 | 20篇 |
| 2015年 | 26篇 |
| 2014年 | 29篇 |
| 2013年 | 34篇 |
| 2012年 | 31篇 |
| 2011年 | 36篇 |
| 2010年 | 20篇 |
| 2009年 | 36篇 |
| 2008年 | 55篇 |
| 2007年 | 35篇 |
| 2006年 | 19篇 |
| 2005年 | 17篇 |
| 2004年 | 27篇 |
| 2003年 | 32篇 |
| 2002年 | 17篇 |
| 2001年 | 17篇 |
| 2000年 | 19篇 |
| 1999年 | 3篇 |
| 1997年 | 4篇 |
| 1993年 | 2篇 |
| 1992年 | 5篇 |
| 1991年 | 4篇 |
| 1990年 | 2篇 |
| 1989年 | 3篇 |
| 1987年 | 6篇 |
| 1986年 | 5篇 |
| 1985年 | 9篇 |
| 1984年 | 3篇 |
| 1983年 | 1篇 |
| 1982年 | 2篇 |
| 1980年 | 3篇 |
| 1979年 | 1篇 |
| 1978年 | 3篇 |
| 1977年 | 3篇 |
| 1976年 | 1篇 |
| 1975年 | 2篇 |
| 1974年 | 1篇 |
| 1973年 | 1篇 |
| 1972年 | 4篇 |
| 1971年 | 1篇 |
| 1970年 | 1篇 |
| 1969年 | 3篇 |
| 1968年 | 1篇 |
排序方式： 共有660条查询结果，搜索用时 15 毫秒
1.
2.
3.
A system dynamic model for epidemics of Blumeria graminis (powdery mildew) on wheat was elaborated, based on the interaction between stages of the disease cycle, weather conditions and host characteristics. The model simulates the progress of disease severity, expressed as a percentage of powdered leaf area, on individual leaves, with a time step of one day, as a result of two processes: the growth of fungal colonies already present on the leaves and the appearance of new colonies. By means of mathematical equations, air temperature, vapour pressure deficit, rainfall and wind are used to calculate incubation, latency and sporulation periods, the growth of pathogen colonies, infection and spore survival. Effects of host susceptibility to infection, and of leaf position within the plant canopy, are also included. Model validation was carried out by comparing model outputs with the dynamics of epidemics observed on winter wheat grown at several locations in northern Italy (1991–98). Simulations were performed using meteorological data measured in standard meteorological stations. As there was good agreement between model outputs and actual disease severity, the model can be considered a satisfactory simulator of the effect of environmental conditions on the progress of powdery mildew epidemics. 相似文献
4.
A dynamic simulation model for the risk of Fusarium head blight on wheat was elaborated based on systems analysis. The model calculates a daily infection risk based on sporulation, spore dispersal and infection of host tissue of the four main species causing the disease (Gibberella zeae, Fusarium culmorum, Gibberella avenacea, Monographella nivalis). Spore yield and dispersal are calculated as functions of temperature, rainfall and relative humidity, while the main factors affecting the infection rate are temperature, wetness and the host growth stage. The model also calculates a risk for mycotoxin production by G. zeae and F. culmorum in the infected head tissue. First validations against field data, collected in some wheat‐growing areas in northern Italy and not used in model elaboration, produced satisfactory results. 相似文献
5.
P. Battilani V. Rossi B. Girometta M. Delos J. Rouzet N. Andr S. Esposito 《EPPO Bulletin》2003,33(3):427-431
Diaporthe helianthi is the causal agent of a severe sunflower disease but, in Italy, disease outbreaks are sporadic with no significant losses. The present work investigates the role of meteorological conditions on the potential development of D. helianthi epidemics in Italy, using the French model Asphodel, which simulates the effect of air temperature, relative humidity and rainfall on ascospore maturation and dispersal, infection establishment, disease onset and severity during the period of host susceptibility. Meteorological data measured in eight stations distributed from north to south Italy, over a 5‐year period (1995–99), was used as model input. Results showed that meteorological conditions in Italy are frequently favourable for D. helianthi infections on sunflower, and severe epidemics are possible. Therefore, climatic conditions are not a limiting factor for disease development in the Italian sunflower‐growing areas. The lack of disease epidemics in Italy may be related to differences in the pathogen populations compared with the French ones. 相似文献
6.
Federica Morandi DVM MS Gregory B. Daniel DVM MS Rebecca E. Gompf DVM MS Anne Bahr DVM MS 《Veterinary radiology & ultrasound》2004,45(2):97-102
Diagnosing right-to-left congenital cardiac shunts can be difficult. Cardiac catheterization and angiocardiography represent the traditional gold standard for diagnosis, but they are invasive. Nuclear scintigraphy using 99mTc-macroaggregated albumin (MAA) has been employed in humans as an alternate method of diagnosis. This study reviews eight dogs presented for evaluation of a suspect right-to-left cardiac shunt that were examined using 99mTc-MAA. In all, 2-4 mCi (74-148 MBq) of reduced particle 99mTc-MAA were injected IV in a cephalic vein and static images of the whole body, including right and left lateral, dorsal, and ventral views, were acquired for 60 s and stored into a 256 x 256 x 16 matrix. Shunt fractions were calculated. One dog with radiopharmaceutical distribution limited to the lungs did not have a shunt. Seven dogs had distribution of the radiopharmaceutical outside the pulmonary capillary bed, indicating bypassing of the pulmonary capillary circulation due to a right-to-left shunt. Four dogs had 99mTc-MAA within the brain. Three dogs that did not have brain uptake, but instead had a sharp cutoff of radioactivity at the level of the front limbs and neck, were diagnosed with reverse patent ductus arteriosus (PDA). The asymmetric distribution of the radiopharmaceutical is due to the location of the shunt, distal to the brachiocephalic trunk and left subclavian artery. Shunt fractions of dogs with extrapulmonary radioactivity ranged from 40% to 59%. Nuclear scintigraphy with 99mTc-MAA is a quick alternative method of diagnosing right-to-left cardiac shunts that permits quantification of shunt fraction. Distinguishing between reverse PDA and other right-to-left shunts may be possible based on the radiopharmaceutical distribution. 相似文献
7.
Fractional excretion of electrolytes in volume‐responsive and intrinsic acute kidney injury in dogs: Diagnostic and prognostic implications 
下载免费PDF全文
下载免费PDF全文 8.
9.
Context
Regime shifts are well known for driving penetrating ecological change, yet we do not recognise the consequences of these shifts much beyond species diversity and productivity. Sound represents a multidimensional space that carries decision-making information needed for some dispersing species to locate resources and evaluate their quantity and quality.Objectives
Here we assessed the effect of regime shifts on marine soundscapes, which we propose has the potential function of strengthening the positive or negative feedbacks that mediate ecosystem shifts.Methods
We tested whether biologically relevant cues are altered by regime shifts in kelp forests and seagrass systems and how specific such shifted soundscapes are to the type of driver; i.e. local pollution (eutrophication) vs. global change (ocean acidification).Results
Here, we not only provide the first evidence for regime-shifted soundscapes, but also reveal that the modified cues of shifted ecosystems are similar regardless of spatial scale and type of environmental driver. Importantly, biological sounds can act as functional cues for orientation by dispersing larvae, and observed shifts in soundscape loudness may alter this function.Conclusions
These results open the question as to whether shifted soundscapes provide a functional role in mediating the positive or negative feedbacks that govern the arrival of species associated with driving change or stasis in ecosystem state.10.