全文获取类型
收费全文 | 4881篇 |
免费 | 179篇 |
国内免费 | 3篇 |
专业分类
林业 | 245篇 |
农学 | 202篇 |
基础科学 | 36篇 |
750篇 | |
综合类 | 1269篇 |
农作物 | 223篇 |
水产渔业 | 310篇 |
畜牧兽医 | 1528篇 |
园艺 | 110篇 |
植物保护 | 390篇 |
出版年
2023年 | 22篇 |
2022年 | 26篇 |
2021年 | 62篇 |
2020年 | 73篇 |
2019年 | 94篇 |
2018年 | 91篇 |
2017年 | 83篇 |
2016年 | 91篇 |
2015年 | 65篇 |
2014年 | 85篇 |
2013年 | 183篇 |
2012年 | 259篇 |
2011年 | 339篇 |
2010年 | 188篇 |
2009年 | 145篇 |
2008年 | 331篇 |
2007年 | 337篇 |
2006年 | 376篇 |
2005年 | 321篇 |
2004年 | 331篇 |
2003年 | 304篇 |
2002年 | 302篇 |
2001年 | 58篇 |
2000年 | 36篇 |
1999年 | 48篇 |
1998年 | 50篇 |
1997年 | 28篇 |
1996年 | 36篇 |
1995年 | 37篇 |
1994年 | 30篇 |
1993年 | 36篇 |
1992年 | 31篇 |
1991年 | 31篇 |
1990年 | 30篇 |
1989年 | 37篇 |
1988年 | 27篇 |
1987年 | 32篇 |
1986年 | 21篇 |
1985年 | 27篇 |
1984年 | 32篇 |
1983年 | 25篇 |
1982年 | 23篇 |
1981年 | 26篇 |
1980年 | 23篇 |
1979年 | 15篇 |
1978年 | 17篇 |
1977年 | 18篇 |
1976年 | 19篇 |
1975年 | 16篇 |
1974年 | 24篇 |
排序方式: 共有5063条查询结果,搜索用时 15 毫秒
11.
Baroni E Matthias RR Marcellin-Little DJ Vezzoni A Stebbins ME 《American journal of veterinary research》2003,64(5):586-589
OBJECTIVES: To evaluate the accuracy of 2 radiographic methods used to assess tibial plateau slope (TPS) in dogs and evaluate effects of film digitization and radiographic beam placement on TPS measurements. SAMPLE POPULATION: 16 hind limbs from dog cadavers weighing > 20 kg. PROCEDURES: Radiographs of tibiae were made with the radiographic beam centered over the stifle joint and midshaft of the tibia. Tibiae were collected, the femorotibial contact area was determined, and slope of the medial tibial condyle in relation to the tibial shaft was measured. Radiographs were digitized. Slope of the medial tibial condyle was measured on printed and digitized radiographs read in random order by 6 examiners unaware of anatomic measurements. Three examiners used a conventional measuring technique, and 3 examiners used an alternative measuring technique. RESULTS: Anatomic measurements were significantly higher than radiographic measurements made by use of the conventional interpretation method but did not differ from radiographic measurements made by use of the alternate method. Measurements from printed radiographs were lower than measurements from digitized radiographs for the 4 most experienced examiners. CONCLUSIONS AND CLINICAL RELEVANCE: Measurements made by use of a line tangential to the cranial, linear portion of the medial tibial condyle at the femorotibial contact point were accurate measurements of the anatomic TPS. Measurements made by use of the conventional TPS measurement method underestimated the anatomic TPS. Measurements made on digitized radiographs were typically more accurate than measurements made on printed radiographs. 相似文献
12.
13.
Anne Fischer Anne Liljander Heike Kaspar Cecilia Muriuki Hans-Henrik Fuxelius Erik Bongcam-Rudloff Etienne P de Villiers Charlotte A Huber Joachim Frey Claudia Daubenberger Richard Bishop Mario Younan Joerg Jores 《Veterinary research》2013,44(1):86
Camels are the most valuable livestock species in the Horn of Africa and play a pivotal role in the nutritional sustainability for millions of people. Their health status is therefore of utmost importance for the people living in this region. Streptococcus agalactiae, a Group B Streptococcus (GBS), is an important camel pathogen. Here we present the first epidemiological study based on genetic and phenotypic data from African camel derived GBS. Ninety-two GBS were characterized using multilocus sequence typing (MLST), capsular polysaccharide typing and in vitro antimicrobial susceptibility testing. We analysed the GBS using Bayesian linkage, phylogenetic and minimum spanning tree analyses and compared them with human GBS from East Africa in order to investigate the level of genetic exchange between GBS populations in the region. Camel GBS sequence types (STs) were distinct from other STs reported so far. We mapped specific STs and capsular types to major disease complexes caused by GBS. Widespread resistance (34%) to tetracycline was associated with acquisition of the tetM gene that is carried on a Tn916-like element, and observed primarily among GBS isolated from mastitis. The presence of tetM within different MLST clades suggests acquisition on multiple occasions. Wound infections and mastitis in camels associated with GBS are widespread and should ideally be treated with antimicrobials other than tetracycline in East Africa. 相似文献
14.
Grewal JS McClure SR Booth LC Evans RB Caston SS 《Journal of the American Veterinary Medical Association》2004,225(12):1881-1888
OBJECTIVE: To characterize the normal ultrasonographic appearance of the podotrochlear apparatus in horses by use of standardized measurements and identify soft tissue changes associated with navicular syndrome. DESIGN: Prospective study. ANIMALS: 7 clinically normal horses and 28 horses with navicular syndrome. PROCEDURE: The feasibility of identifying and measuring the soft tissue structures of the podotrochlear apparatus ultrasonographically via the transcuneal approach was assessed in 2 additional horses without navicular syndrome; both horses were euthanatized, and the structures identified ultrasonographically were confirmed at necropsy. Ultrasonographs were obtained in the study horses. Objective and subjective data were obtained to characterize ultrasonographic changes associated with navicular syndrome. RESULTS: Abnormalities of the flexor surface of the distal sesamoid (navicular) bone, the impar ligament, the distal digital annular ligament, deep digital flexor tendon (DDFT), and the podotrochlear (navicular) bursa were assessed via the transcuneal ultrasonographic approach. No significant differences were found between the measurements of the podotrochlear apparatus in normal horses and those with navicular syndrome; however, important subjective differences were detected ultrasonographically in horses with navicular syndrome. In horses with navicular syndrome, ultrasonographic findings were indicative of navicular bursitis, dystrophic mineralization of the DDFT and impar ligament, tendonitis and insertional tenopathy of the DDFT, desmitis of the impar ligament, and cortical changes in the flexor surface of the navicular bone. CONCLUSIONS AND CLINICAL RELEVANCE: Findings of ultrasonographic evaluation of the hoof appear to be useful in determining the cause of caudal heel pain and characterizing the components of navicular syndrome in horses. 相似文献
15.
Chris Garforth Kevin McKemey Tahir Rehman Richard Tranter Richard Cooke Julian Park Peter Dorward Chris Yates 《Livestock Science》2006,103(1-2):158-168
Unidentified heats contribute to declining fertility rates in English dairy herds. Several techniques have been advocated to improve heat detection rates. Despite demonstrable technical efficacy and cost-effectiveness, uptake is low. A study in South West England used the Theory of Reasoned Action (TORA) to explore dairy farmers' attitudes and beliefs towards heat detection techniques. Few farmers were convinced that following prescribed observation times, milk progesterone testing and using pedometers would fit their system or improve on their current heat detection practices. Perceived difficulty of using a technique was not a constraint on adoption. Without promotion that addresses identified barriers and drivers to adoption, little change in current practice can be expected. 相似文献
16.
Context
Spatial variation in abundance is influenced by local- and landscape-level environmental variables, but modeling landscape effects is challenging because the spatial scales of the relationships are unknown. Current approaches involve buffering survey locations with polygons of various sizes and using model selection to identify the best scale. The buffering approach does not acknowledge that the influence of surrounding landscape features should diminish with distance, and it does not yield an estimate of the unknown scale parameters.Objectives
The purpose of this paper is to present an approach that allows for statistical inference about the scales at which landscape variables affect abundance.Methods
Our method uses smoothing kernels to average landscape variables around focal sites and uses maximum likelihood to estimate the scale parameters of the kernels and the effects of the smoothed variables on abundance. We assessed model performance using a simulation study and an avian point count dataset.Results
The simulation study demonstrated that estimators are unbiased and produce correct confidence interval coverage except in the rare case in which there is little spatial autocorrelation in the landscape variable. Canada warbler abundance was more highly correlated with site-level measures of NDVI than landscape-level NDVI, but the reverse was true for elevation. Canada warbler abundance was highest when elevation in the surrounding landscape, defined by an estimated Gaussian kernel, was between 1300 and 1400 m.Conclusions
Our method provides a rigorous way of formally estimating the scales at which landscape variables affect abundance, and it can be embedded within most classes of statistical models.17.
Sarah L. Rawlings Richard J. OConnell Jonathan R. Green 《Physiological and Molecular Plant Pathology》2007,70(4-6):110-119
The spores (conidia) of the bean anthracnose fungal pathogen, Colletotrichum lindemuthianum, adhere to the aerial parts of plants to initiate the infection process. In previous studies we have shown that the Colletotrichum spores are surrounded by a fibrillar spore coat, comprising several major glycoproteins. Previous evidence showed that a monoclonal antibody (UB20) that recognised these glycoproteins was able to inhibit adhesion of spores to a hydrophobic surface. In this paper we have further studied the role of the spore coat in adhesion, germination and fungal development by studying the effects of UB20 and protease treatment of spores. The latter treatment has previously been shown to remove the spore coat. Spores germinate on glass, polystyrene and water agar, however, appressoria only develop on glass or polystyrene, showing a requirement for a hard surface. Removal of the spore coat with protease inhibits adhesion at 30 min, before the secretion of ECM glycoproteins. Protease treatment also inhibits the development of appressoria and reduces pathogenicity on leaves. Incubation of spores with the MAb UB20 inhibits adhesion at 30 min, but does not affect appressorium formation or pathogenicity. The results suggest that an intact spore coat has two functions; it is required for adhesion to a hydrophobic surface and for the detection of a hard surface necessary for appressorium formation. We suggest that contact with a hard surface, rather than adhesion, is the key event leading to appressorium formation. 相似文献
18.
19.
Emaga Thomas Happi Bindelle Jérôme Agneesens Richard Buldgen André Wathelet Bernard Paquot Michel 《Tropical animal health and production》2011,43(1):171-177
Musa sp. peels are widely used by smallholders as complementary feeds for cattle in the tropics. A study of the influence of the
variety and the maturation stage of the fruit on fermentability and metabolisable energy (ME) content of the peels was performed
using banana (Yangambi Km5) and plantain (Big Ebanga) peels at three stages of maturation in an in vitro model of the rumen.
Peel samples were analysed for starch, free sugars and fibre composition. Samples were incubated in the presence of rumen
fluid. Kinetics of gas production were modelled, ME content was calculated using prediction equation and short-chain fatty
acids production and molar ratio were measured after 72 h of fermentation. Final gas production was higher in plantain (269–339 ml
g−1) compared to banana (237–328 ml g−1) and plantain exhibited higher ME contents (8.9–9.7 MJ/kg of dry matter, DM) compared to banana (7.7–8.8 MJ/kg of DM). Butyrate
molar ratio decreased with maturity of the peels. The main influence of the variety and the stage of maturation on all fermentation
parameters as well as ME contents of the peels was correlated to changes in the carbohydrate fraction of the peels, including
starch and fibre. 相似文献
20.
Effects of diet restriction on life span and age-related changes in dogs 总被引:11,自引:0,他引:11
Kealy RD Lawler DF Ballam JM Mantz SL Biery DN Greeley EH Lust G Segre M Smith GK Stowe HD 《Journal of the American Veterinary Medical Association》2002,220(9):1315-1320
OBJECTIVE: To evaluate the effects of 25% diet restriction on life span of dogs and on markers of aging. DESIGN: Paired feeding study. ANIMALS: 48 Labrador Retrievers. PROCEDURES: Dogs were paired, and 1 dog in each pair was fed 25% less food than its pair-mate from 8 weeks of age until death. Serum biochemical analyses were performed, body condition was scored, and body composition was measured annually until 12 years of age. Age at onset of chronic disease and median (age when 50% of the dogs were deceased) and maximum (age when 90% of the dogs were deceased) life spans were evaluated. RESULTS: Compared with control dogs, food-restricted dogs weighed less and had lower body fat content and lower serum triglycerides, triiodothyronine, insulin, and glucose concentrations. Median life span was significantly longer for dogs in which food was restricted. The onset of clinical signs of chronic disease generally was delayed for food-restricted dogs. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that 25% restriction in food intake increased median life span and delayed the onset of signs of chronic disease in these dogs. 相似文献