全文获取类型
收费全文 | 602篇 |
免费 | 19篇 |
专业分类
林业 | 68篇 |
农学 | 11篇 |
基础科学 | 3篇 |
143篇 | |
综合类 | 62篇 |
农作物 | 35篇 |
水产渔业 | 69篇 |
畜牧兽医 | 179篇 |
园艺 | 11篇 |
植物保护 | 40篇 |
出版年
2023年 | 8篇 |
2022年 | 5篇 |
2021年 | 14篇 |
2020年 | 20篇 |
2019年 | 20篇 |
2018年 | 23篇 |
2017年 | 20篇 |
2016年 | 11篇 |
2015年 | 14篇 |
2014年 | 21篇 |
2013年 | 29篇 |
2012年 | 31篇 |
2011年 | 56篇 |
2010年 | 23篇 |
2009年 | 27篇 |
2008年 | 44篇 |
2007年 | 40篇 |
2006年 | 35篇 |
2005年 | 26篇 |
2004年 | 28篇 |
2003年 | 20篇 |
2002年 | 31篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 6篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1992年 | 2篇 |
1990年 | 3篇 |
1988年 | 7篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1972年 | 1篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1961年 | 1篇 |
1959年 | 1篇 |
1951年 | 1篇 |
1931年 | 1篇 |
排序方式: 共有621条查询结果,搜索用时 15 毫秒
581.
Alan M. Norris DVM Elizabeth J. Laing DVM DVSc Victor E. O. Valli DVM PhD Stephen J. Withrow DVM Dennis W. Macy DVM Gregory K. Ogilvie DVM Jim Tomlinson DVM Dudley McCaw DVM Guy Pidgeon DVM Robert M. Jacobs DVM PhD 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1992,6(3):145-153
One hundred and fifteen dogs with neoplasms of the lower urinary tract (bladder and/or urethra) were retrospectively evaluated at five referral institutions participating in ongoing studies by the Veterinary Cooperative Oncology Group. Most tumors were malignant (97%) and of epithelial origin (97%). Lower urinary tract tumors were more common in older dogs weighing greater than 10 kg. The following significant (P less than 0.05) statistical associations were found using the University of Guelph hospital population as control; there was no sex predisposition although the female:male ratio was 1.95:1. Neutered dogs were predisposed as were Airedale Terriers, Beagles, and Scottish Terriers, whereas German Shepherds were significantly under-represented among dogs with lower urinary tract tumors. These statistical associations should be interpreted cautiously because of possible demographic differences in hospital populations among the University of Guelph and other cooperating institutions. There were no significant correlations between age, gender, weight, breed, response to therapy, and survival time. Clinical signs were indicative of lower urinary tract disease and included hematuria, stranguria, and pollakiuria. The laboratory data were nonspecific except for urinalysis test results. Hematuria and inflammatory urinary sediments were most commonly reported; neoplastic cells were identified in the urine sediment of 30% of dogs with lower urinary tract tumors. Contrast cystography was a useful noninvasive diagnostic method since 96% of the dogs had a mass or filling defect in the lower urinary tract demonstrated by this technique.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
582.
583.
Lin CM Jeng CR Hsiao SH Liu JP Chang CC Chiou MT Tsai YC Chia MY Pang VF 《Veterinary microbiology》2011,149(1-2):72-84
The immunopathogenesis of porcine circovirus type 2 (PCV2) infection in conventional pigs is complicated by various environmental factors and individual variation and is difficult to be completely reproduced experimentally. In the present field-based study, a tissue microarray (TMA) consisting of a series of lymphoid follicles having different PCV2-loads was constructed using formalin-fixed and paraffin-embedded superficial inguinal lymph nodes (LNs) from 102 pigs. Using the TMA, a wide range of parameters, including co-infected viral pathogens, immune cell subsets, and cell apoptosis/proliferation activity by immunohistochemical (IHC) staining or in situ hybridization (ISH) were measured, characterized, and compared. The signal location and area extent of each parameter were interpreted by pathologists, semi-quantified by automated image analysis software, and analyzed statistically. The results herein demonstrated a significant negative correlation between PCV2 and CD79a (p<0.001) and a significant positive correlation between PCV2 and lysozyme (p<0.001) or TUNEL (p<0.001) using Pearson correlation analysis. The amount of porcine respiratory and reproductive syndrome virus (PRRSV) and porcine parvovirus antigens did not correlate with the tissue loads of PCV2 nucleic acid. Multiple regression analysis further predicted that PCV2 contributed major effects on CD79a, lysozyme, and TUNEL but PRRSV showed relatively less effects on these parameters. In addition, the total signal intensity of Ki67 (index of cell proliferation activity) did not change significantly among cases with different PCV2 loads; however, as the loading of PCV2 nucleic acid increased, the main contribution of Ki67 signal gradually shifted from B cells in the germinal center to T cells and macrophages in the interfollicular regions. In the present study, the use of TMA to establish a mathematical model with a wider range of statistical analysis can bring us a step forward to understand the immunopathogenesis of PCV2 infection-associated follicular changes in LNs. 相似文献
584.
Kamila Câmara Correia João Victor Jansen de Queiroz Ricardo Brainer Martins Alessandro Nicoli Emerson Medeiros Del Ponte Sami Jorge Michereff 《European journal of plant pathology / European Foundation for Plant Pathology》2017,149(2):269-276
A standard area diagram set (SADs) with eight severity values ranging from 0.5 to 32% was evaluated as a tool to improve the accuracy of the estimates of Phomopsis leaf blight severity on eggplant by ten inexperienced raters. A first assessment in a 50-leaf dataset of digital images was performed unaided (UN, no SAD). Two further aided (A) assessments, conducted two (A1) and four weeks after the first (A2) unaided one were performed. The precision of the estimates, as indicated by the Pearson’s correlation coefficient (r), improved significantly when using the aid (A1: r = 0.96 and A2: r = 0.96) compared to unaided (UN: r = 0.79). However, the generalized bias (C b) was not significantly affected because the unaided estimates were already quite accurate (C b = 0.93). The overall concordance (ρ c) was significantly improved due to the large gains in precision when using the SADs. The raters’ estimates were more uniform (ρ c > 0.9) when using the aid, with progressive gains in the reliability of the estimates among them, indicated by the concordance correlation coefficient statistics. The SADs proposed in this study will be useful in severity estimation during field work involving multiple raters, especially as use of the SADs results in less variable estimates, improving accuracy and reliability among raters. 相似文献
585.
Emmanuel Amoah Boakye Dibi N’da Hyppolite Victor Rex Barnes Stefan Porembski 《Arid Land Research and Management》2017,31(2):219-233
Understanding the impacts of agricultural land use is desired for proper management of riparian forests buffers (RFs) in savannas. In this light, we analyzed the relationship between woody plant diversity and soil properties of RFs in farmlands (FAs) and protected areas (PAs) along Afram (Guinean zone) and Tankwidi (Sudanian zone) Rivers located within the Volta sub-basin of Ghana. ALOS-AVNIR imageries were used to map RFs to facilitate sampling of soil and woody vegetation (dbh ≥5?cm) using stratified randomized design (72 plots; size: 500?m2 each) for the analysis of soil physical and chemical properties and Shannon-Wiener plant species diversity. Although the fractions of sand, silt, and clay varied between the PAs and FAs, they were predominantly categorized as sandy loam. Along the Afram River, there were no significant differences in the concentrations and nutrient stocks of soil C, N, P, and K as well as the pH, moisture content, and bulk density between PA and FA. For the Tankwidi River, the concentrations and nutrient stocks of C and K significantly decreased from PA to FA while N, P, pH, bulk density, and moisture content were not different. Of the soil attributes measured C, N, P, pH, ground slope, and soil moisture had significant relationships with the diversity and density of the riparian woody plants. Controlling agricultural activities in riparian forests could preserve soil properties similar to that found in protected areas. 相似文献
586.
587.
Oscar F Santos‐Amaya Clébson S Tavares João Victor C Rodrigues Silverio O Campos Raul Narciso C Guedes Analiza P Alves Eliseu José G Pereira 《Pest management science》2017,73(1):i-i
The cover image, by Oscar Fernando Santos‐Amaya et al., is based on the Research Article Fitness costs and stability of Cry1Fa resistance in Brazilian populations of Spodoptera frugiperda, DOI: 10.1002/ps.4312 . Photo Credit: Dr. Oscar Santos‐Amaya.
588.
Dionisio Andújar Victor Rueda-Ayala José Dorado Roland Gerhards César Fernández-Quintanilla 《Gesunde Pflanzen》2014,66(1):17-22
Sorghum halepense (L.) Pers. is one of the most troublesome weeds in warm climates. Its control is difficult, and understanding the factors affecting its spreading is crucial. A study was conducted in 47 commercial maize fields, which account for more than 400 ha in the Spanish provinces of Albacete, Badajoz and Madrid, to analyse the distribution of S. halepense as a function of various agricultural variables. The results showed significant effects of agricultural management on the presence of this weed. Crop rotation decreased the infestation of S. halepense. Furrow irrigation system favored the establishment of large patches with high plant density, while the sprinkler irrigation system favored the presence of isolated plants or small patches. Apparently, moldboard tillage promoted the establishment of large patches. The combination of different variables also had effects on the characteristics of the present infestations, and its management could lead to a better control in maize fields. 相似文献
589.
Roland Gerhards Michael Spth Markus Skefeld Gerassimos G. Peteinatos Adnan Nabout Victor Rueda Ayala 《Weed Research》2021,61(1):68-77
Precision farming technologies were implemented into a commercial harrow to increase selectivity of weed harrowing in spring cereals. Digital cameras were mounted before and after the harrow measuring crop cover. Crop soil cover (CSC) was computed out of these two images. Eight field experiments were carried out in spring cereals. Mode of harrowing intensity was changed in four experiments by speed, number of passes and tine angle. Each mode was varied in five intensities. In four experiments, only intensity of harrowing was changed. Weed control efficacy (WCE) and CSC were measured immediately after harrowing. Crop recovery was assessed 14 days after harrowing. Modes of intensity were not significantly different. However, intensity had significant effects on WCE and CSC. Cereals recovered from 10% CSC, and selectivity was in the constant range at 10% CSC. Therefore, 10% CSC was the threshold for the decision algorithm. If the actual CSC was below 10% CSC, intensity was increased. If the actual CSC was higher than 10%, intensity was decreased. Image analysis, decision support system and automatic control of harrowing intensity by hydraulic adjustment of tine angle were installed on a controller mounted on the harrow. The new system was tested in an additional field study. Threshold values for CSC were set at 10%, 30% and 60%. Automatic tine angle adjustment precisely realised the three different CSC values with variations of 1.5% to 3%. This development contributes to selective weed control and supports farmers during harrowing. 相似文献
590.
Ron Porat Victor Vinokur Batia Weiss Lea Cohen Avinoam Daus Eliezer E. Goldschmidt Samir Droby 《European journal of plant pathology / European Foundation for Plant Pathology》2003,109(9):901-907
-Aminobutyric acid (BABA), an inducer of pathogen resistance in plants, induced disease resistance in reproductive parts of the plant, such as grapefruit peel tissue. Application of BABA to specific wound sites on the fruit peel surface induced resistance to Penicillium digitatum, the main postharvest pathogen of citrus fruit, in a concentration-dependent manner, being most effective at 20mM, and rather less effective at either higher or lower concentrations. The effect of BABA in inducing resistance to P. digitatum in the fruit peel surface was local and limited to the vicinity (within 1–2cm) of the BABA-treated site. In addition to inducing pathogen resistance, increasing concentrations of BABA (from 1 to 100mM) also exhibited direct antifungal activity and inhibited P. digitatum spore germination and germ tube elongation in vitro. The induction of resistance to P. digitatum by BABA was accompanied by the activation of various pathogen defense responses in grapefruit peel tissue, including activation of chitinase gene expression and protein accumulation after 48h, and an increase in phenylalanine ammonia lyase (PAL) activity after 72h. 相似文献