全文获取类型
收费全文 | 850篇 |
免费 | 63篇 |
专业分类
林业 | 28篇 |
农学 | 7篇 |
75篇 | |
综合类 | 255篇 |
农作物 | 23篇 |
水产渔业 | 57篇 |
畜牧兽医 | 402篇 |
园艺 | 8篇 |
植物保护 | 58篇 |
出版年
2021年 | 13篇 |
2020年 | 17篇 |
2019年 | 9篇 |
2018年 | 14篇 |
2017年 | 13篇 |
2016年 | 10篇 |
2015年 | 16篇 |
2014年 | 19篇 |
2013年 | 24篇 |
2012年 | 23篇 |
2011年 | 26篇 |
2010年 | 18篇 |
2009年 | 14篇 |
2008年 | 30篇 |
2007年 | 55篇 |
2006年 | 50篇 |
2005年 | 44篇 |
2004年 | 39篇 |
2003年 | 51篇 |
2002年 | 39篇 |
2001年 | 39篇 |
2000年 | 31篇 |
1999年 | 20篇 |
1998年 | 9篇 |
1996年 | 5篇 |
1995年 | 7篇 |
1994年 | 11篇 |
1993年 | 5篇 |
1992年 | 26篇 |
1991年 | 12篇 |
1990年 | 21篇 |
1989年 | 17篇 |
1988年 | 13篇 |
1987年 | 11篇 |
1986年 | 10篇 |
1985年 | 12篇 |
1984年 | 9篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1977年 | 5篇 |
1975年 | 7篇 |
1974年 | 8篇 |
1973年 | 6篇 |
1972年 | 9篇 |
1971年 | 7篇 |
1970年 | 6篇 |
1969年 | 5篇 |
1948年 | 8篇 |
排序方式: 共有913条查询结果,搜索用时 15 毫秒
151.
Relationships of dead wood patterns with biophysical characteristics and ownership according to scale in Coastal Oregon,USA 总被引:1,自引:0,他引:1
Dead wood patterns and dynamics vary with biophysical factors, disturbance history, ownership, and management practices; the
relative importance of these factors is poorly understood, especially at landscape to regional scales. This study examined
current dead wood amounts in the Coastal Province of Oregon, USA, at multiple spatial scales. Objectives were to: (1) describe
current regional amounts of several characteristics of dead wood; (2) compare dead wood amounts across ownerships; (3) determine
the relative importance, according to spatial scale, of biophysical and ownership characteristics, to regional dead wood abundance.
Dead wood plot data were evaluated with respect to explanatory variables at four spatial scales of resolution: plots, subwatersheds,
watersheds and subbasins. The relationships of dead wood characteristics with biophysical attributes and ownership were diverse
and scale-specific. Region-wide dead wood abundance and types varied among ownerships, with public lands typically having
higher amounts of dead wood and more large dead wood than private lands. Regression analysis of total dead wood volume indicated
that ownership was important at the subbasin scale. Growing season moisture stress was important at plot, subwatershed, and
watershed scales. Topography was important at the two coarser scales. Multivariate analysis of dead wood gradients showed
that ownership was important at all scales, topography at the subbasin scale, historical vegetation at watershed and subbasin
scales, and current vegetation at plot and subwatershed scales. Management for dead wood and related biodiversity at watershed
to landscape scales should consider the distinct dynamics of snags and logs, the importance of historical effects, and the
relevance of ownership patterns. 相似文献
152.
Two depth profiles of the osmium concentration and the 187Os/186Os isotopic ratio in the Indian Ocean showed that the osmium concentration seems to be unaltered by chemical or biological processes occuring in seawater; accordingly, osmium is conservative. These data were obtained from an experimental method that eliminated the problems related to osmium preconcentration. This method led to a new evaluation of the concentration of osmium in seawater; the mean concentration of osmium and the 187Os/186Os ratio are equal to 10.86 +/- 0.07 picograms per kilogram and 8.80 +/- 0.07, respectively. The results suggest the existence of an organocomplex that dominates the speciation of osmium in seawater. 相似文献
153.
L J Kennedy S D Carter A Barnes S Bell D Bennett B Ollier W Thomson 《Veterinary immunology and immunopathology》1999,69(2-4):101-111
Although 36 DLA-DRB1 and 10 DLA-DQA1 allele sequences have been published to date, no data on individual allele frequencies exists, either for specific breeds or cross breeds, and the full extent of the polymorphism at each of these loci is still not known. We have used sequence-specific oligonucleotide probing (SSOP) to characterise a series of 367 dogs for their DRB1 and DQA1 alleles. These included individual animals from over 60 different breeds, with numbers per breed ranging from 1 to 39. DLA types were generated from 218 dogs for DRB1 and from 330 dogs for DQA1, while 181 dogs were characterised for both these loci. The frequency of individual DRB1 and DQA1 alleles showed considerable interbreed variation, e.g. 83% of West Highland White Terriers were DRB1*01 as opposed to 9% of Collies. No breed had >9 of the 22 DRB1 types defined in this study; several breeds had only two DRB1 types. DLA-DQA1 showed less variation in allele numbers per breed, but also showed considerable interbreed frequency variation. Haplotype analysis revealed over 44 different DRB1/DQA1 combinations. Of these, 25 were in a number of animals, and also in an animal that was homozygous for one or both of these loci. Some DRB1 alleles could be found in combination with several different DQA1 alleles, while others were only present in one haplotypic combination. DLA allele frequency data in normal dogs will be critical for disease association studies. It may also be possible to use haplotype data to establish the genetic relationships between different dog breeds. 相似文献
154.
An assessment of carcass counting surveys with increasing time lapse following a simulated fish kill on a small upland stream 下载免费PDF全文
A simulated fish kill was conducted on a small upland stream in Northern Ireland by planting out hatchery‐produced brown trout Salmo trutta L. carcasses of various size categories. Standard, post‐fish kill, assessment walkover surveys were conducted over time intervals to determine the number of carcasses visible. The sample variance between individual surveyors was generally low, with good agreement between the observed counts for the three, discrete, size fractions of fish up to 72 hr after the simulated fish kill. Despite low discharge rates, shallow water and good accessibility to the experimental stream, only 52% of the small category fish (<8 cm LF) were recorded 4 hr after the start of the simulated fish kill. Larger carcasses (>17 cm LF) were more visible, and >90% were detected 48 hr after the start of the simulated fish kill. After 96 hr, all size fractions of carcasses had reduced significantly, and the variability between replicate surveys increased markedly. 相似文献
155.
156.
157.
158.
K. Brenner K.R. Harkin G.A. Andrews G. Kennedy 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2009,23(1):67-71
Background: This study describes compound failure of the endocrine and exocrine pancreas in Greyhounds, a condition that has not been reported in the veterinary literature.
Objective: To describe the clinical and pathologic findings in 12 Greyhounds with juvenile pancreatic atrophy.
Animals: Ten Greyhounds presented for necropsy examination and 2 sibling Greyhounds presented for clinical evaluation before necropsy, all with a history of small-bowel diarrhea.
Procedures: Retrospective study of laboratory and pathologic findings in 12 Greyhounds, including serum trypsin-like immunoreactivity assays, oral glucose tolerance testing, and serum anti-insulin antibody concentrations.
Results: Gross pancreatic atrophy was found in all 12 dogs. Histopathologic lesions were found in both the endocrine and exocrine pancreas and included acinar cell apoptosis, zymogen granule loss, cytoplasmic clearing or vacuolar change, lobular atrophy, islet loss, and lymphocytic or lymphoplasmacytic pancreatitis. Antemortem test results on the 2 Greyhound puppies indicated concurrent exocrine pancreatic insufficiency (EPI) and insulin-dependent diabetes mellitus (IDDM).
Conclusions and Clinical Importance: Compound failure of the exocrine and endocrine pancreas is rarely reported in dogs and neither disease is well recognized in the Greyhound. This condition is of potential economic importance to the Greyhound racing industry. 相似文献
Objective: To describe the clinical and pathologic findings in 12 Greyhounds with juvenile pancreatic atrophy.
Animals: Ten Greyhounds presented for necropsy examination and 2 sibling Greyhounds presented for clinical evaluation before necropsy, all with a history of small-bowel diarrhea.
Procedures: Retrospective study of laboratory and pathologic findings in 12 Greyhounds, including serum trypsin-like immunoreactivity assays, oral glucose tolerance testing, and serum anti-insulin antibody concentrations.
Results: Gross pancreatic atrophy was found in all 12 dogs. Histopathologic lesions were found in both the endocrine and exocrine pancreas and included acinar cell apoptosis, zymogen granule loss, cytoplasmic clearing or vacuolar change, lobular atrophy, islet loss, and lymphocytic or lymphoplasmacytic pancreatitis. Antemortem test results on the 2 Greyhound puppies indicated concurrent exocrine pancreatic insufficiency (EPI) and insulin-dependent diabetes mellitus (IDDM).
Conclusions and Clinical Importance: Compound failure of the exocrine and endocrine pancreas is rarely reported in dogs and neither disease is well recognized in the Greyhound. This condition is of potential economic importance to the Greyhound racing industry. 相似文献
159.
E.H. Appleman B.S. Sachais R. Patel K.J. Drobatz R.P. Groman D.R. Kennedy P.A. O'Donnell C. Bryan M.B. Callan 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2009,23(1):138-145
Background: Platelet cryopreservation allows long-term storage and immediate availability of transfusion products.
Hypothesis: The addition of a preparation inhibiting platelet activation (Thrombosol, in 2% dimethyl sulfoxide [DMSO]) will enhance in vitro function and prolong in vivo survival of cryopreserved platelets compared with those preserved in 6% DMSO.
Animals: Thirty-three research dogs.
Methods: Prospective study. Eleven fresh canine apheresis platelet concentrates (PCs) were each split into 3 units: fresh and cryopreserved in 6% DMSO or Thrombosol. Platelet analysis, performed 1–10 weeks postfreezing, included in vitro functional testing and in vivo survival assessed by administration of biotinylated platelets.
Results: Platelet aggregation was diminished in cryopreserved PC. Cryopreserved platelets could be activated, as based on mean thrombin-stimulated P-selectin expression (6% DMSO, 23.0%; Thrombosol, 18.4%), although to a lesser extent than fresh PC (49.1%) ( P < .0001). The mean maximum in vivo platelet recovery for fresh PC was 80.3%, significantly greater than recovery for 6% DMSO (49.2%) and Thrombosol PC (43.7%) ( P ≤ .001). The half-life (days) of fresh PC (3.8 ± 0.4) was significantly ( P < .002) greater than that of 6% DMSO (1.9 ± 1.0) and Thrombosol (2.4 ± 1.1) PC, with no difference ( P = .3) between cryopreserved PC.
Conclusions and Clinical Importance: Cryopreservation of canine platelets using Thrombosol did not provide any advantage over preservation using 6% DMSO. Cryopreserved platelets can be activated in vitro and provide therapeutic benefit when fresh platelets are unavailable. Further studies are needed to assess their in vivo hemostatic function. 相似文献
Hypothesis: The addition of a preparation inhibiting platelet activation (Thrombosol, in 2% dimethyl sulfoxide [DMSO]) will enhance in vitro function and prolong in vivo survival of cryopreserved platelets compared with those preserved in 6% DMSO.
Animals: Thirty-three research dogs.
Methods: Prospective study. Eleven fresh canine apheresis platelet concentrates (PCs) were each split into 3 units: fresh and cryopreserved in 6% DMSO or Thrombosol. Platelet analysis, performed 1–10 weeks postfreezing, included in vitro functional testing and in vivo survival assessed by administration of biotinylated platelets.
Results: Platelet aggregation was diminished in cryopreserved PC. Cryopreserved platelets could be activated, as based on mean thrombin-stimulated P-selectin expression (6% DMSO, 23.0%; Thrombosol, 18.4%), although to a lesser extent than fresh PC (49.1%) ( P < .0001). The mean maximum in vivo platelet recovery for fresh PC was 80.3%, significantly greater than recovery for 6% DMSO (49.2%) and Thrombosol PC (43.7%) ( P ≤ .001). The half-life (days) of fresh PC (3.8 ± 0.4) was significantly ( P < .002) greater than that of 6% DMSO (1.9 ± 1.0) and Thrombosol (2.4 ± 1.1) PC, with no difference ( P = .3) between cryopreserved PC.
Conclusions and Clinical Importance: Cryopreservation of canine platelets using Thrombosol did not provide any advantage over preservation using 6% DMSO. Cryopreserved platelets can be activated in vitro and provide therapeutic benefit when fresh platelets are unavailable. Further studies are needed to assess their in vivo hemostatic function. 相似文献