全文获取类型
收费全文 | 496篇 |
免费 | 49篇 |
专业分类
林业 | 9篇 |
农学 | 7篇 |
基础科学 | 2篇 |
99篇 | |
综合类 | 77篇 |
农作物 | 27篇 |
水产渔业 | 18篇 |
畜牧兽医 | 289篇 |
园艺 | 5篇 |
植物保护 | 12篇 |
出版年
2023年 | 4篇 |
2020年 | 8篇 |
2019年 | 8篇 |
2017年 | 8篇 |
2016年 | 6篇 |
2015年 | 10篇 |
2014年 | 12篇 |
2013年 | 48篇 |
2012年 | 20篇 |
2011年 | 19篇 |
2010年 | 14篇 |
2009年 | 14篇 |
2008年 | 14篇 |
2007年 | 16篇 |
2006年 | 23篇 |
2005年 | 25篇 |
2004年 | 13篇 |
2003年 | 22篇 |
2002年 | 9篇 |
2001年 | 18篇 |
2000年 | 12篇 |
1999年 | 11篇 |
1997年 | 8篇 |
1996年 | 4篇 |
1994年 | 5篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 13篇 |
1989年 | 11篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 11篇 |
1984年 | 4篇 |
1983年 | 8篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1977年 | 5篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1973年 | 6篇 |
1972年 | 4篇 |
1971年 | 4篇 |
1970年 | 6篇 |
1968年 | 4篇 |
1967年 | 5篇 |
1936年 | 3篇 |
1897年 | 3篇 |
1896年 | 3篇 |
排序方式: 共有545条查询结果,搜索用时 31 毫秒
101.
102.
基于改进Bayes抠图算法的麦穗小穗自动计数方法 总被引:1,自引:1,他引:0
小麦产量评估需人工获取田间单位面积的麦穗数和麦穗小穗数,往往耗时耗力。为了实现高效、自动地麦穗小穗计数,提出一种基于改进Bayes抠图算法的麦穗小穗自动计数方法。该方法首先利用改进Bayes抠图算法对获取地自然生长条件下的麦穗图像进行抠图,将麦穗从自然背景中分割出来。然后对该图像进行平滑滤波和二值化,运用迭代极限腐蚀运算对二值化图像进行腐蚀处理,去除麦穗图像中的麦芒,分离出麦穗上每个单独的麦穗小穗。再运用面积滤波滤除掉面积过小的区域,对剩余区域的黑洞进行填充,由此每个单独的麦穗小穗形成一个单独的连通区域,最后对连通区域进行标记和计数,完成麦穗小穗的自动计数。使用4个小麦品种的麦穗图像对麦穗上的小穗进行计数验证,结果表明,该方法在识别4个品种田间麦穗单幅图像中小穗数量的平均计数精度达到94.53%,平均相对误差为5.47%,对比已有麦穗小穗自动计数方法,计数精度显著提高,这对于小麦在线产量预估具有重要意义。 相似文献
103.
We studied the response of nodal segments of Eucalyptus microtheca F.J. Muell. to salt stress in a tissue culture system. Three clones of Eucalyptus microtheca (37, 42 and 43) were grown in vitro under saline conditions (0-140 mM NaCl) for three months. The survival of all three clones decreased with increasing concentrations of NaCl in the medium, but the presence of up to 70 mM NaCl stimulated rooting in Clones 37 and 42. Shoot elongation of Clone 43 was less affected by salt than that of Clones 37 and 42. Leaf growth, expressed as leaf length, was stimulated 40% in Clone 42 and 33% in Clone 43, but was progressively inhibited up to 27% by 70 mM NaCl in Clone 37. Massive accumulation of Na(+) and Cl(-) occurred, especially in Clones 42 and 43 (4000 and 3000 mmol Na(+) kg(DW) (-1), respectively), as the salinity of the culture solution increased, and this was correlated with inhibition of growth. Because of a reduction in the accumulation of K(+) with increasing salinity, the K(+)/Na(+) ratio decreased from a control value of 4.5 to 0.14 in shoots grown in the presence of 140 mM NaCl. The development of techniques for selecting seedlings by monitoring the physiology of shoots in vitro instead of testing whole plants in vivo will provide a relatively simple method of selection for woody trees. 相似文献
104.
105.
Merchant M Mills K Williams S Kleckley F Sims A Elsey RM Bushnell J 《Veterinary immunology and immunopathology》2006,111(3-4):315-320
Alligators were injected intraperitoneally with four different doses (10, 1.0, 0.1, and 0.01 mg/kg body weight) of a mixture of bacterial lipopolysaccharides (LPS) derived from three different types of bacteria (Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumoniae). Injection of the alligators with the LPS mixture resulted in a dose- and time-dependent increase in total peripheral leukocytes Lymphocytes increased at days 3 and 4 post-injection, and decreased back to baseline levels at day 7 for all doses. Alligators that were not treated, and those injected with pyrogen-free saline, did not exhibit statistically significant changes in total leukocytes during the course of the study. Injection of alligators with 0.5 mg LPS/kg body weight derived from one of three bacterial species revealed that the leukocyte increases observed were not statistically different for all three types of LPS. The animals displayed the same increases in total counts and the levels of all circulating leukocyte types were not different between animals treated with a combination of LPS from all three bacterial species. 相似文献
106.
Merchant ME Leger N Jerkins E Mills K Pallansch MB Paulman RL Ptak RG 《Veterinary immunology and immunopathology》2006,110(3-4):221-228
Leukocytes were isolated from whole blood of wild alligators by differential sedimentation. The leukocytes were disrupted in 5% AcOH and the crude extracts processed by ultrafiltration. The extracts were subjected to solvent exchange (0.1% AcOH) and the fraction that contained macromolecules between 1 and 10 kDa were subjected to further analyses. The acid extracts of the alligator leukocytes exhibited substantial antimycotic activities against six of eight species of Candida yeast tested. In addition, the alligator leukocyte extracts were effective as antimicrobial agents against 10 of 12 bacterial species, and displayed moderate activity against two enveloped viruses (human immunodeficiency virus-1 and herpes simplex virus-1HF). Kinetic analyses revealed that the antimycotic effects of the leukocyte extract occurred rapidly, with 64% fungal growth inhibition within 3 min of exposure. The molecule(s) responsible for the antimicrobial activities were sensitive to proteases, heat-stable, acid soluble, and in the 1–10 kDa range. These data suggest that alligator leukocytes express cationic peptides that are responsible for their antimicrobial properties. 相似文献
107.
Erin L. Koen Jeff Bowman Colin J. Garroway Stephen C. Mills Paul J. Wilson 《Landscape Ecology》2012,27(1):29-43
Landscape heterogeneity can influence animal dispersal by causing a directional bias in dispersal rate, as certain landscape
configurations might promote, impede, or prevent movement and gene flow. In forested landscapes, logging operations often
contribute to heterogeneity that can reduce functional connectivity for some species. American martens (Martes americana) are one such species, as they are considered specialists of late-seral coniferous forests. We assessed marten gene flow
to test the hypothesis that habitat management has maintained landscape connectivity for martens in the managed forests of
Ontario, Canada. We genotyped 653 martens at 12 microsatellite loci, sampled from 29 sites across Ontario. We expected that
if forest management has an effect on marten gene flow, we would see a correlation between effective resistance, estimated
by circuit theory, and genetic distance, estimated by population graphs. Although we found a positive relationship between
effective resistance and genetic distance (Mantel r = 0.249, P < 0.001), marten gene flow was better described by isolation by Euclidean distance (Mantel r = 0.410, P < 0.001). Our results suggest that managed forests in Ontario are well connected for marten and neither impede nor promote
marten gene flow at the provincial scale. 相似文献
108.
109.
Khor KH Campbell F Rathbone MJ Greer RM Mills PC 《Journal of Feline Medicine and Surgery》2012,14(2):99-106
This study was designed to evaluate the cats' acceptance and compliance of the owners and cats towards an extemporaneously prepared palatable compounded atenolol (paste and suspension) formulation in comparison to the commercially obtained tablet, in a randomised, cross-over study design.The three formulations were prescribed twice daily for 6 days to 13 healthy privately-owned cats of 13 different owners, with varying levels of experience in medicating cats. Daily compliance was evaluated via an owner-completed diary, completed after each dose administered. Owner's experience and preference of the formulation was evaluated via questionnaires given prior to, at the end of each treatment protocol, and upon completion of the study. Although compounded suspension was association with fewest missed doses, the majority of cat owners expressed a preference for the divided tablet. Atenolol tablets, compounded paste and suspension acceptance and compliance were comparable. Further work is now required to assess the amount and stability of the active ingredient and the robustness of the paste and suspension formulations prior to any bioavailability comparisons between the formulations. 相似文献
110.
Helen E. Zulch Daniel S. Mills Ruth Lambert Robert M. Kirberger 《Journal of Veterinary Behavior: Clinical Applications and Research》2012,7(4):252-258
A 30-month-old Labrador retriever bitch with a history of atopy was presented for acute-onset tail biting that was leading to self-mutilation. The problem began 8 months before consultation and was resolved after 2 months, but it recurred 3 months later and continued for 3 months until the time of consultation. The current episode was difficult to interrupt and was being controlled through the use of an Elizabethan collar. There had been no history of injury to the tail. On examination of the tail, an irregularity was palpated approximately midway on the dorsal surface. Radiographs of the tail showed soft-tissue swelling cranially and presence of an ossicle between the mid-caudal vertebrae. Mutilation stopped with administration of tramadol and paracetamol and started again when the medication was discontinued. No behavior modification was implemented. Although there is a possibility that the tramadol was treating a psychogenically driven self-mutilation behavior, it is more likely that pain was the initiating cause for the behavior. This case report highlights the importance of careful medical evaluation of suspected behavioral problems and discusses the possible use of tramadol in self-mutilation. 相似文献