全文获取类型
收费全文 | 1036篇 |
免费 | 38篇 |
国内免费 | 3篇 |
专业分类
林业 | 10篇 |
农学 | 19篇 |
基础科学 | 16篇 |
47篇 | |
综合类 | 526篇 |
农作物 | 14篇 |
水产渔业 | 11篇 |
畜牧兽医 | 261篇 |
园艺 | 23篇 |
植物保护 | 150篇 |
出版年
2021年 | 8篇 |
2019年 | 8篇 |
2018年 | 9篇 |
2017年 | 14篇 |
2016年 | 8篇 |
2015年 | 12篇 |
2014年 | 11篇 |
2013年 | 28篇 |
2012年 | 49篇 |
2011年 | 51篇 |
2010年 | 26篇 |
2009年 | 12篇 |
2008年 | 49篇 |
2007年 | 47篇 |
2006年 | 56篇 |
2005年 | 44篇 |
2004年 | 59篇 |
2003年 | 57篇 |
2002年 | 48篇 |
2001年 | 38篇 |
2000年 | 51篇 |
1999年 | 26篇 |
1997年 | 8篇 |
1996年 | 6篇 |
1995年 | 11篇 |
1994年 | 7篇 |
1993年 | 14篇 |
1992年 | 25篇 |
1991年 | 24篇 |
1990年 | 15篇 |
1989年 | 15篇 |
1988年 | 11篇 |
1987年 | 22篇 |
1986年 | 10篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1981年 | 8篇 |
1980年 | 9篇 |
1978年 | 6篇 |
1976年 | 6篇 |
1973年 | 13篇 |
1972年 | 10篇 |
1971年 | 11篇 |
1970年 | 9篇 |
1969年 | 6篇 |
1968年 | 8篇 |
1967年 | 10篇 |
1966年 | 13篇 |
排序方式: 共有1077条查询结果,搜索用时 15 毫秒
1.
Comparison of Outcome After Use of Extra‐Luminal Rings and Intra‐Luminal Stents for Treatment of Tracheal Collapse in Dogs 下载免费PDF全文
2.
Estimating the Sensitivity and Specificity of Real‐Time Quantitative PCR of Fecal Samples for Diagnosis of Rhodococcus equi Pneumonia in Foals 下载免费PDF全文
S.D. Shaw N.D. Cohen M.K. Chaffin G.P. Blodgett M. Syndergaard D. Hurych 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2015,29(6):1712-1717
Background
Real‐time, quantitative PCR (qPCR) methods for detecting Rhodococcus equi in feces have been developed as a noninvasive, rapid diagnostic test for R. equi pneumonia, but have not been evaluated in a large population of foals.Objective
The objective of this study was to evaluate the clinical utility of fecal PCR as a diagnostic test for R. equi pneumonia in foals using receiver operating characteristic (ROC) methods.Animals
186 foals born in 2011 at an R. equi‐endemic ranch in Texas.Methods
Fecal samples were collected at the time of onset of clinical signs for pneumonic foals (n = 31). Foals with pneumonia were matched by age and birth date to healthy (n = 31) and subclinical (n = 124) control foals; fecal samples were collected from these controls. DNA was extracted from feces using commercial kits and concentration of virulent R. equi in feces was determined by qPCR.Results
Concentration of R. equi in feces differed significantly (P < .05) among groups. The area under the ROC curve for fecal qPCR for diagnosis of R. equi pneumonia was 89% (95% CI, 83–99), with a sensitivity of 94% and specificity of 72%.Conclusions and Clinical Importance
qPCR of feces can be useful as an alternative to tracheobronchial aspiration for the diagnosis of R. equi in foals with clinical signs of pneumonia. Caution should be used in extrapolating results of this study to other populations because fecal concentration of R. equi might vary by geographic location or management practices. 相似文献3.
Summary
Lycopersicon pimpenellifolium L3707, resistant to the late blight oomycete Phytophthora infestans was crossed with the susceptible Lycopersicon pimpenellifolium 14377 or the susceptible Lycopersicon esculentum ZH. Progeny F1 and F2 generations were scored at the 5-leaf stage for resistance against 175 field and recombinant isolates of the pathogen. F1 plants exhibited various levels of moderate resistance and F2 plants segregated 3:6:7 resistant/moderately resistant/susceptible. The data support the hypothesis that race-non-specific resistance in L3707 is controlled by two independent genes: a partially-dominant gene and a dominant epistatic gene. 相似文献
4.
Summary Several varieties of Cucurbita moschata were found resistant to cucumber mosaic virus (CMV). Inter-specific hybridization between C. pepo and a CMV resistant variety of C. moschata resulted in partial fertile hybrids which set F2 seeds. Cotyledonary inoculation of F2 seedlings with CMV brought various results, depending on seasonal differences and developmental stages at which observations were made. Resistance to CMV generally declined under conditions of low temperature, short days and low light intensity. 相似文献
5.
Summary Seedlings of Trifolium repens showed considerable variation with regard to the morphology and growth of their calli, and their ability for in vitro differentiation of shoots. One of the lines selected for regeneration in primary callus cultures also showed shoot formation from protoplasts. Somatic embryogenesis in callus cultures of T. pratense and T. arvense occurred only in selected seedling lines. This paper highlights the importance of screening a large number of plants within a cultivar of outbreeding species to achieve reproducible plant regeneration from tissue culture. 相似文献
6.
A model for optimal operation of water supply/irrigation systems of various water quality sources, with treatment plants, multiple water quality conservative factors, and dilution junctions is presented. The objective function includes water cost at the sources, water conveyance costs which account for the hydraulics of the network indirectly, water treatment cost, and yield reduction costs of irrigated crops due to irrigation with poor quality water. The model can be used for systems with supply by canals as well as pipes, which serve both drinking water demands of urban/rural consumers and field irrigation requirements. The general nonlinear optimization problem has been simplified by decomposing it to a problem with linear constraints and nonlinear objective function. This problem is solved using the projected gradient method. The method is demonstrated for a regional water supply system in southern Israel that contains 39 pipes, 37 nodes, 11 sources, 10 agricultural consumers, and 4 domestic consumers. The optimal operation solution is described by discharge and salinity values for all pipes of the network. Sensitivity of the optimal solution to changes in the parameters is examined. The solution was found to be sensitive to the upper limit on drinking water quality, with total cost being reduced by 5% as the upper limit increases from 260 to 600 mg Cl l–1. The effect of income from unit crop yield is more pronounced. An increase of income by a factor of 20 results in an increase of the total cost by a factor of 3, thus encouraging more use of fresh water as long as the marginal cost of water supply is smaller than the marginal decrease in yield loss. The effect of conveyance cost becomes more pronounced as its cost increases. An increase by a factor of 100 results in an increase of the total cost by about 14%. The network studied has a long pipe that connects two distinct parts of the network and permits the supply of fresh water from one part to the other. Increasing the maximum permitted discharge in this pipe from 0 to 200 m3 h–1 reduces the total cost by 11%. Increasing the maximum discharge at one of the sources from 90 to 300 m3 h–1 reduces the total cost by about 8%. 相似文献
7.
Determining transpiration from meteorological data and crop characteristics for irrigation management 总被引:3,自引:0,他引:3
Summary Traditional meteorological estimates of evapotranspiration include empirical crop factors which are inadequate for scheduling high frequency irrigation. The performance of a transpiration model was tested and adapted to suit the operational requirements of automated irrigation systems. Hourly measurements of global solar radiation, air temperature, humidity and wind speed, obtained from an automatic weather station are inputs to the model. Additional inputs include daily updated data of plant height and leaf area index. This information is processed to determine the active coupling surface between the crop and the atmosphere. The model takes into account the resistance of the leaf to diffusion of water vapor.Calculated transpiration, based on the model, matched very closely measurements of latent heat flux in an irrigated cotton field. It was also in good agreement with water uptake measured in stems of the cotton plants using a heat pulse technique. The test also showed that implementation of the model in the field under study would have improved the efficiency of water application.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel, No. 1855-E, 1986 series 相似文献
8.
Avia E. Rubin Ayelet-Chen Werdiger Mathias Blum Ulrich Gisi Helge Sierotzki Dietrich Hermann Yigal Cohen 《European journal of plant pathology / European Foundation for Plant Pathology》2011,129(2):339-351
Wild type (WT) field isolates of Bremia lactucae failed to germinate in vitro or infect lettuce leaves in the presence of CAA (carboxylic acid amide) fungicides. Minimal
inhibitory concentrations (MIC) for mandipropamid, dimethomorph, benthiavalicarb and iprovalicarb were 0.005, 0.5, 0.5 and
5 μg ml−1, respectively. Mutagenesis experiments showed that spores exposed to EMS (ethyl methane sulphonate) or UV irradiation (254 nm)
could infect lettuce leaves in the presence of up to 100 μg ml−1 CAA. The proportion of infected leaves relative to the number of spores inoculated (infection frequency) was inversely related
to the concentration of CAA used, ranging between 0 and 160 per 1 × 106 spores. Resistant mutants (RM) lost their resistance within 1–14 reproduction cycles on CAA-treated plants. Crosses were
made between RMxWT isolates and RMxRM isolates with an attempt to obtain stable homozygous resistant off-springs. Such crosses
yielded few resistant but unstable progeny isolates. Mutagenic treatments given to hybrid isolates also failed to produce
stable resistance. Previous gene sequencing data showed that stable resistance to CAAs is based on a single SNP in the cellulose synthase 3 (CesA3) gene of Plasmopara viticola. Therefore, we sequenced a 582 bp DNA fragment of Ces3A of WT, RM and hybrid isolates of B.lactucae. No mutation in this gene fragment was found. We conclude that mutagenic agents like EMS or UV may induce resistance to CAA
in Bremia lactucae but this resistance is not stable and not linked to mutations in CesA3 gene. 相似文献
9.
We studied the photostabilizing effect of the isoquinoline alkaloid berberine on the following three model photounstable biocontrol agents: the bacterium Bacillus thuringiensis ( Bt ), the baculovirus Spodoptera littoralis nucleopolyhedrosis virus ( SlNPV ), and the entomopathogenic fungus Beauveria bassiana . The photoprotection provided by berberine was evaluated following various periods of simulated sunlight-UV irradiation. Insecticidal activity of Bt and SlNPV , as well as the rate of B. bassiana spore germination served as parameters for the photostabilizing effects. Only a berberine- Bt complex is effective, as practically no photostabilization was evident by just mixing the two components. The UV-sensitive SlNPV and B. bassiana spores were considerably photostabilzed by berberine. The role of the cationic nature of the berberine molecule and the importance of its absorbance spectrum in photostabilization of biocontrol agents are discussed. 相似文献
10.
IMAGING DIAGNOSIS—USE OF RADIOGRAPHY,COMPUTED TOMOGRAPHY,AND ENDOSCOPY IN THE DIAGNOSIS OF ESOPHAGEAL PERFORATION BY AN EXTRA‐LUMINAL TRACHEAL RING PROSTHESIS IN A GOLDEN RETRIEVER 下载免费PDF全文
A 6‐year‐old neutered male, Golden retriever presented with regurgitation and excitement‐induced coughing. Two years prior, extra‐thoracic tracheal collapse was diagnosed and extra‐luminal tracheal ring prostheses were placed. Radiographs at presentation showed mineralized and undulant cervical tracheal cartilages. A dorsally broad‐based soft tissue opacity bulged into the caudal cervical tracheal lumen. Esophageal dysmotility and barium accumulation were identified at this level on contrast esophography. Computed tomography showed migration of a prosthetic tracheal ring, resulting in perforation of the esophagus. Hair, foreign material, and dynamic tracheal narrowing were identified on esophagoscopy and tracheoscopy, respectively. Esophagostomy and foreign body removal were performed. 相似文献