全文获取类型
收费全文 | 2105篇 |
免费 | 162篇 |
专业分类
林业 | 54篇 |
农学 | 43篇 |
基础科学 | 7篇 |
237篇 | |
综合类 | 389篇 |
农作物 | 59篇 |
水产渔业 | 103篇 |
畜牧兽医 | 1209篇 |
园艺 | 38篇 |
植物保护 | 128篇 |
出版年
2023年 | 16篇 |
2021年 | 26篇 |
2020年 | 32篇 |
2019年 | 36篇 |
2018年 | 38篇 |
2017年 | 48篇 |
2016年 | 44篇 |
2015年 | 35篇 |
2014年 | 50篇 |
2013年 | 87篇 |
2012年 | 73篇 |
2011年 | 99篇 |
2010年 | 51篇 |
2009年 | 43篇 |
2008年 | 76篇 |
2007年 | 88篇 |
2006年 | 70篇 |
2005年 | 71篇 |
2004年 | 76篇 |
2003年 | 80篇 |
2002年 | 87篇 |
2001年 | 59篇 |
2000年 | 77篇 |
1999年 | 50篇 |
1998年 | 15篇 |
1996年 | 12篇 |
1995年 | 22篇 |
1993年 | 12篇 |
1992年 | 40篇 |
1991年 | 48篇 |
1990年 | 41篇 |
1989年 | 27篇 |
1988年 | 26篇 |
1987年 | 33篇 |
1986年 | 34篇 |
1985年 | 34篇 |
1984年 | 20篇 |
1983年 | 29篇 |
1982年 | 12篇 |
1979年 | 32篇 |
1978年 | 16篇 |
1977年 | 15篇 |
1976年 | 13篇 |
1973年 | 17篇 |
1972年 | 20篇 |
1971年 | 24篇 |
1970年 | 29篇 |
1969年 | 12篇 |
1967年 | 17篇 |
1966年 | 18篇 |
排序方式: 共有2267条查询结果,搜索用时 78 毫秒
21.
Zhai Changyuan Long John Taylor Randal Weckler Paul Wang Ning 《Precision Agriculture》2020,21(3):589-602
Precision Agriculture - With recent developments allowing increased planter speeds, improving spatial uniformity of crop emergence will continue to be an important focus of research. Vertical... 相似文献
22.
Evidence for genetic distinction among sympatric ecotypes of Arctic char (Salvelinus alpinus) in south‐western Alaskan lakes 下载免费PDF全文
Shannan L. May‐McNally Thomas P. Quinn Pamela J. Woods Eric B. Taylor 《Ecology of Freshwater Fish》2015,24(4):562-574
Resource polymorphism may play an important role in the process of speciation. The Arctic char (Salvelinus alpinus) exhibits great phenotypic and genetic diversity across its range, making it an ideal species for studies of resource polymorphism and divergence. Here, we investigated genetic variation at 11 microsatellite loci among 287 Arctic char from five isolated yet proximate postglacial lakes in south‐western Alaska that were previously examined for resource polymorphism. Significant differences in pairwise FST were detected among all lakes (range from 0.05 to 0.28, all P < 0.02). In one lake (Lower Tazimina Lake), we found evidence for two genetic groups of char and for significant differences in the distribution of microsatellite variability among at least two of the three previously described body size morphotypes (‘large’‐, ‘medium’‐, and ‘small’‐bodied char; maximum FST = 0.09; differences in admixture proportions). We also found a significant association between genetic admixture proportions and gill raker counts among body size morphs (r = ?0.73, P < 0.001). Our data represent the first record of genetically distinct sympatric morphs of Arctic char in Alaska and provide further evidence that differences in morphology associated with feeding (gill rakers) and growth trajectories reflect niche diversification and promote genetic divergence in Holarctic populations of Arctic char. 相似文献
23.
Preliminary investigation comparing a detomidine continuous rate infusion combined with either morphine or buprenorphine for standing sedation in horses 下载免费PDF全文
24.
In the Upper Zambezi and Okavango ecoregions, Brycinus lateralis, Hepsetus cuvieri, Schilbe intermedius and Serranochromis macrocephalus are important in subsistence fisheries, while S. intermedius and S. macrocephalus are often caught in commercial catches. Despite their importance, there is little information on their age and growth and age validation. Growth zone deposition rate in otoliths of B. lateralis, H. cuvieri, S. intermedius and S. macrocephalus was validated as annual using edge analysis in this study. Annual deposition of growth zones was corroborated by a fluorochrome marking experiment. Both methods demonstrated that one growth zone was deposited annually. Edge analysis demonstrated that the highest proportion of opaque zones was detected between August and December, most likely as a result of slow growth during lower temperature water during the preceding winter. With growth zone deposition validated as annual, future research should focus on determining the growth, maturity and mortality rates of these species, parameters which are important for their management. 相似文献
25.
Australian Cattle Dogs with Neuronal Ceroid Lipofuscinosis are Homozygous for a CLN5 Nonsense Mutation Previously Identified in Border Collies 下载免费PDF全文
A. Kolicheski G.S. Johnson D.P. O'Brien T. Mhlanga‐Mutangadura D. Gilliam J. Guo T.D. Anderson‐Sieg R.D. Schnabel J.F. Taylor A. Lebowitz B. Swanson D. Hicks Z.E. Niman F.A. Wininger M.C. Carpentier M.L. Katz 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2016,30(4):1149-1158
26.
Evaluation of Serum Aspergillus‐Specific Immunoglobulin A by Indirect ELISA for Diagnosis of Feline Upper Respiratory Tract Aspergillosis 下载免费PDF全文
27.
Evason MD Taylor SM Bebchuk TN 《The Canadian veterinary journal. La revue veterinaire canadienne》2007,48(3):296-298
A 4.5-month-old, male domestic shorthair was presented with bilateral femoral fractures after falling from a low height. Radiographs revealed reduced radio-opacity and thin cortices of all long bones. A presumptive diagnosis of osteodystrophy, secondary to osteogenesis imperfecta, was made on postmortem examination. 相似文献
28.
The aims of this study were to develop a new real-time quantitative PCR (QPCR) assay based on IS900 for detection and quantification of Mycobacterium avium subsp. paratuberculosis (MAP) DNA in faeces, and to use this to detect infected sheep. Both the C and S strains of MAP were detected by the QPCR assay, and no cross reactions were detected with 51 other species of mycobacteria including 10 which contained IS900-like sequences. One copy of IS900 fragment cloned into plasmid pCR2.1 and 1 fg of MAP genomic DNA were consistently detected, while in spiked faecal samples the detection limit was 10 viable MAP per gram of ovine faeces. A total of 506 individual ovine faecal samples and 27 pooled ovine faecal samples with known culture results were tested. The QPCR assay detected 68 of 69 BACTEC culture positive individual faeces and there was a strong relation between time to detection in culture and DNA quantity measured by QPCR (r= -0.70). In pooled faecal samples, QPCR also agreed with culture (kappa=0.59). MAP DNA was detected from some culture negative faecal samples from sheep exposed to MAP, suggesting that the QPCR has very high analytical sensitivity for MAP in faecal samples and detects non-viable MAP in ovine faeces. None of the faecal samples from 176 sheep that were not exposed to MAP were positive in QPCR. This is the first report of a direct faecal QPCR assay that has similar sensitivity to a gold standard radiometric culture assay. 相似文献
29.
Wathes DC Cheng Z Bourne N Taylor VJ Coffey MP Brotherstone S 《Domestic animal endocrinology》2007,33(2):203-225
During the early postpartum period dairy cows mobilize fat and muscle to support lactation. This is associated with alterations in blood metabolite and hormone profiles which in turn influence milk yield and fertility. This study developed models to determine how metabolic traits, milk yield and body condition score were inter-related at different times in the periparturient period and to compare these relationships in primiparous (PP, n=188) and multiparous (MP, n=312) cows. Data from four previous studies which included information on blood metabolic parameters, parity, milk yield, body condition score and diet were collated into a single dataset. Coefficients of polynomial equations were calculated for each trait between -1 week pre-calving and week +7 postpartum using residual maximum likelihood modelling. The completed dataset was used in a multiple correlation model to determine how the best fit curves were related to each other over time. PP cows had higher concentrations of insulin-like growth factor-I and lower beta-hydroxybutyrate concentrations throughout, higher leptin concentrations pre-partum and both the peak in non-esterified fatty acids and the nadir in urea concentration occurred earlier after calving. These differences were associated with significantly lower milk production. Leptin concentrations fell at calving and were related to body condition score. Insulin was negatively correlated with yield in MP cows only. In MP cows the relationship between insulin-like growth factor-I and yield switched from negative to positive between weeks +4 and +7. Both beta-hydroxybutyrate and urea were positively related to yield in PP cows. In contrast, in MP cows beta-hydroxybutyrate was negatively correlated with yield and urea was strongly related to body condition score but not yield. These results suggest that there are differences in the control of tissue mobilization between PP and MP cows which may promote nutrient partitioning into growth as well as milk during the first lactation. 相似文献
30.
The goal in the therapeutic use of mesenchymal stem cells (MSCs) in musculoskeletal disease is to harness the regenerative nature of these cells focussing on their potential to grow new tissues and organs to replace damaged or diseased tissue. Laboratory isolation of MSCs is now well established and has recently been demonstrated for equine MSCs. Stem cell science has attracted considerable interest in both the scientific and clinical communities because of its potential to regenerate tissues. Research into the use of MSCs in tissue regeneration in general reflects human medical needs, however, the nature, prevalence and prognosis of superficial digital flexor tendonitis has put equine veterinary science at the forefront of tendon regeneration research. Much has been investigated and learnt but it must be appreciated that in spite of this, the field is still relatively young and both communities must prepare themselves for considerable time and effort to develop the technology into a highly efficient treatments. The promise of functional tissue engineering to replace old parts with new fully justifies the interest. At present, however, it is important to balance the understanding of our current limitations with a desire to progress the technology. 相似文献