全文获取类型
收费全文 | 565篇 |
免费 | 53篇 |
专业分类
林业 | 33篇 |
农学 | 26篇 |
基础科学 | 7篇 |
106篇 | |
综合类 | 24篇 |
农作物 | 41篇 |
水产渔业 | 75篇 |
畜牧兽医 | 242篇 |
园艺 | 17篇 |
植物保护 | 47篇 |
出版年
2024年 | 1篇 |
2023年 | 11篇 |
2022年 | 18篇 |
2021年 | 26篇 |
2020年 | 29篇 |
2019年 | 23篇 |
2018年 | 27篇 |
2017年 | 33篇 |
2016年 | 40篇 |
2015年 | 14篇 |
2014年 | 36篇 |
2013年 | 43篇 |
2012年 | 34篇 |
2011年 | 55篇 |
2010年 | 20篇 |
2009年 | 21篇 |
2008年 | 30篇 |
2007年 | 23篇 |
2006年 | 27篇 |
2005年 | 26篇 |
2004年 | 13篇 |
2003年 | 10篇 |
2002年 | 12篇 |
2001年 | 9篇 |
2000年 | 8篇 |
1999年 | 6篇 |
1998年 | 7篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1976年 | 1篇 |
1945年 | 1篇 |
1927年 | 1篇 |
排序方式: 共有618条查询结果,搜索用时 15 毫秒
201.
Abstract – Rates of annual food consumption and biomass were modeled for several fish species across representative rivers and lakes in eastern North America. Results were combined to assess the relative potential of fish predation to impact zebra mussels ( Dreissena polymorpha ). Predicted annual food consumption by fishes in southern waters was over 100% greater than that in northern systems because of warmer annual water temperatures and presumed increases in metabolic demand. Although generally increasing with latitude, biomasses of several key zebra mussel fish predators did not change significantly across latitudes. Biomasses of some less abundant fish predators did increase significantly with latitude, but increases were not of the magnitude to offset predicted decreases in food consumption. Our results generally support the premise that fishes in rivers and lakes of the southern United States (U.S.) have inherently greater potential to impact zebra mussels by predation. Our simulations may provide a partial explanation of why zebra mussel invasions have not been as rapid and widespread in southern U.S. waters compared to the Great Lakes region. 相似文献
202.
Stevenson MA Sanson RL Miranda AO Lawrence KA Morris RS 《New Zealand veterinary journal》2007,55(6):264-272
To mitigate the effects of risks to food safety and infectious disease outbreaks in farmed animals, animal health authorities need to have systems in place to identify and trace the source of identified problems in a timely manner. In the event of emergencies, these systems will allow infected or contaminated premises (and/or animals) to be identified and contained, and will allow the extent of problems to be communicated to consumers and trading partners in a clear and unambiguous manner. The key to achieving these goals is the presence of an effective animal health decision support system that will provide the facilities to record and store detailed information about cases and the population at risk, allowing information to be reported back to decision makers when it is required. Described here are the components of an animal health decision support system, and the ways these components can be used to enhance food safety, responses to infectious disease incursions, and animal health and productivity. Examples are provided to illustrate the benefit these systems can return, using data derived from countries that have such systems (or parts of systems) in place. Emphasis is placed on the features that make particular system components effective, and strategies to ensure that these are kept up to date. 相似文献
203.
Trypanosomosis caused by Trypanosoma vivax has been a constraint for cattle production in the Bolivian lowlands, since it was introduced in 1996. Flooded areas like the Bolivian Pantanal have a suitable environment for the presence and transmission of Salivarian trypanosomes and farmers from that region often report trypanosomosis-like problems on their farms. The objective of the present study, therefore, was to characterize the epidemiology of bovine trypanosomosis in the Bolivian Pantanal. In order to achieve this objective, 202 cattle from the province of Angel Sandoval and 209 cattle from the province of German Busch were randomly sampled (the Pantanal is located in both provinces). Twenty-nine farms in both provinces were visited, the farmers interviewed, and biologic samples collected from their cattle. Samples were submitted for parasitological and PCR evaluation and the prevalence of bovine trypanosomosis was estimated for each province. Laboratory results were correlated with the sampled animals packed cell volume (PCV) and body condition (BC) scores and the observed T. vivax parasites measured for morphometry analysis. Results from this study show differences in morphometric measures between T. vivax parasites from each province. Differences between provinces were also observed in the T. vivax-related disease situation. While in Angel Sandoval the PCV and BC of T. vivax-affected animals were significantly lower than those of the T. vivax-negative animals, in German Busch no differences were observed in the PCV and BC of T. vivax-positive or negative animals. Animal prevalence of T. vivax in Angel Sandoval was 27.79% (95% CI: 14.52-44.28) and in German Busch was 19.03% (95% CI: 9.19-30.75). The T. evansi animal prevalence in each province was 0.99% (95% CI: 0.27-2.99) and 5.71% (95% CI: 2.43-12.19), respectively. Based on questionnaire and laboratory results, it was concluded that trypanosomosis is a primary constraint for cattle production in the Bolivian Pantanal. 相似文献
204.
Physicochemical characterization and pharmacokinetics in broiler chickens of a new recrystallized enrofloxacin hydrochloride dihydrate
下载免费PDF全文
![点击此处可从《Journal of veterinary pharmacology and therapeutics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
L. Gutierrez J. E. Miranda‐Calderon P. Garcia‐Gutierrez H. Sumano 《Journal of veterinary pharmacology and therapeutics》2015,38(2):183-189
Enrofloxacin, a key antimicrobial agent in commercial avian medicine, has limited bioavailability (60%). This prompted its chemical manipulation to yield a new solvate‐recrystallized enrofloxacin hydrochloride dihydrate entity (enroC). Its chemical structure was characterized by means of mass spectroscopy, Fourier transformed infrared spectroscopy, X‐ray powder diffraction, and thermal analysis. Comparative oral pharmacokinetics (PK) of reference enrofloxacin (enroR) and enroC in broiler chickens after oral administration revealed noticeable improvements in key parameters and PK/PD ratios. Maximum serum concentration values were 2.61 ± 0.21 and 5.9 ± 0.42 μg/mL for enroR and enroC, respectively; mean residence time was increased from 5.50 ± 0.26 h to 6.20 ± 0.71 h and the relative bioavailability of enroC was 336%. Considering Cmax/MIC and AUC/MIC ratios and the MIC values for a wild‐type Escherichia coli O78/H12 (0.25 μg/mL), optimal ratios will only be achieved by enroC (Cmax/MIC = 23.6 and AUC/MIC = 197.7 for enroC; vs. Cmax/MIC = 10.4 and AUC/MIC = 78.1 for enroR). Furthermore, enroC may provide in most cases mutant prevention concentrations (Cmax/MIC ≥ 16). Ready solubility of powder enroC in drinking water at concentrations regularly used (0.01%) to provide an additional advantage of enroC in the field. Further development of enroC is warranted before it can be recommended for clinical use in veterinary medicine. 相似文献
205.
das Araújo Francisca Chagas Bezerra Moura Elisa Ferreira de Rodrigues Simone Miranda de Carvalho Kenny Bonfim Arruda Tavares Eraldo José Madureira Moura Mônika Fecury da Silva Gilvan Ferreira 《Genetic Resources and Crop Evolution》2021,68(5):1809-1824
Genetic Resources and Crop Evolution - The biofortification of cassava (Manihot esculenta Crantz) roots is one of the actual goals of genetic breeding, with the development of roots richer in... 相似文献
206.
Vettorazzi Julio Cesar Fiorio Santa Catarina Renato Poltronieri Tathianne Pastana de Sousa Miranda Daniel Pereira Santana Josefa Grasiela Silva Ramos Helaine Christine Cancela Pereira Messias Gonzaga 《Genetic Resources and Crop Evolution》2021,68(8):3333-3343
Genetic Resources and Crop Evolution - The development of segregating populations in papaya allows the development of new high fruit yield and excellent fruit quality pure line or hybrid cultivars.... 相似文献
207.
Ramiro J. Zepeda Manila Candiracci Nicolas Lobos Sebastian Lux Hugo F. Miranda 《Marine drugs》2014,12(9):5055-5071
Neosaxitoxin (NeoSTX) is a specific reversible blocker of voltage gated sodium channels on excitable cells. In the last decade, it has been tested in a number of interesting clinical trials, however there is still little information available on mammalian toxicity. Rats were treated for 12 weeks with doses of 1, 3 or 6 μg/kg of subcutaneous NeoSTX. At weeks 12 and 17, animals were sacrificed and blood samples collected for hematological and biochemical analysis. Organs were harvested for weight determination and histopathological assessments. The lowest acute toxicity via the intraperitoneal (ip) route was (30.35 μg/kg) and there was no significant difference between intramuscular and subcutaneous routes (11.4 and 12.41 μg/kg). The NeoSTX adiministration did not produce lethality at week 12 and after five weeks of suspension. NeoSTX 6 μg/kg ip produced reductions (p < 0.05) in body weight and food intake, and increased blood level of total and direct bilirubin, GGT and SGOT at week 12; all of these were reversed in the recovery period. NeoSTX 1 and 3 μg/kg ip did not show significant changes with the control group. Histopathological presentations were normal in all groups. This study revealed that NeoSTX is safe in vivo, giving a reliable security margin for its use like a local anesthetic. 相似文献
208.
Duarte Ana Paula Melo Vander Freitas Brown George G. Pauletti Volnei 《Biology and Fertility of Soils》2014,50(5):851-860
Biology and Fertility of Soils - The survival and cast production of the tropical endogeic earthworm Pontoscolex corethrurus and the changes in chemical and physical characteristics induced by gut... 相似文献
209.
Alex Taylor William H. Blake Miranda J. Keith-Roach 《Journal of Soils and Sediments》2014,14(11):1886-1893
Purpose
Estimates of beryllium-7 (7Be) enrichment in soil particle size fractions are important for correction in existing soil redistribution models. Little attention has been given to documenting methods of estimating 7Be enrichment and assessing differences in enrichment between soil types in the context of soil redistribution modelling. Here, we detail a method for estimating 7Be enrichment and correcting soil redistribution estimates.Materials and methods
Beryllium from a solution of BeCl2 was adsorbed to two soils with contrasting texture using a batch procedure. Soil fractions were separated by settling according to Stokes’ Law, and samples of bulk and settled fractions were digested and analysed for Be concentration and for specific surface area.Results and discussion
Both soils demonstrated increasing enrichment of Be with increasing specific surface area. There was a marked difference in enrichment between the soil types with the coarse soil showing greater enrichment in the finer fractions. Calculated enrichment ratios for the coarse soil more than doubled between subfractions of the <63 μm class. Failure to account for the selective transport of fractions during soil redistribution studies could incur substantial errors in soil erosion estimates.Conclusions
Stable Be provides a practical means of estimating 7Be enrichment in soil and subsequent corrections can be incorporated into the conversion model where it is proposed that corrections should be applied to the inventory deficit at each eroding point. The marked difference in enrichment between soil types in these experiments suggested that characterising enrichment and associated correction factors should be done on a site-specific basis. Implementation of the particle size correction procedures requires additional field and laboratory data to standard application of the established soil erosion conversion model. 相似文献210.
Queiroz TM Machado NT Furtado FF Oliveira-Filho AA Alustau MC Figueiredo CS Miranda GE Barbosa-Filho JM Braga VA Medeiros IA 《Marine drugs》2011,9(10):2075-2088
This study aimed to investigate the cardiovascular effects elicited by Dictyota pulchella, a brown alga, using in vivo and in vitro approaches. In normotensive conscious rats, CH(2)Cl(2)/MeOH Extract (CME, 5, 10, 20 and 40 mg/kg) from Dictyota pulchella produced dose-dependent hypotension (-4 ± 1; -8 ± 2; -53 ± 8 and -63 ± 3 mmHg) and bradycardia (-8 ± 6; -17 ± 11; -257 ± 36 and -285 ± 27 b.p.m.). In addition, CME and Hexane/EtOAc Phase (HEP) (0.01-300 μg/mL) from Dictyota pulchella induced a concentration-dependent relaxation in phenylephrine (Phe, 1 μM)-pre-contracted mesenteric artery rings. The vasorelaxant effect was not modified by the removal of the vascular endothelium or pre-incubation with KCl (20 mM), tetraethylammonium (TEA, 3 mM) or tromboxane A(2) agonist U-46619 (100 nM). Furthermore, CME and HEP reversed CaCl(2)-induced vascular contractions. These results suggest that both CME and HEP act on the voltage-operated calcium channel in order to produce vasorelaxation. In addition, CME induced vasodilatation after the vessels have been pre-contracted with L-type Ca(2+) channel agonist (Bay K 8644, 200 nM). Taken together, our data show that CME induces hypotension and bradycardia in vivo and that both CME and HEP induce endothelium-independent vasodilatation in vitro that seems to involve the inhibition of the Ca(2+) influx through blockade of voltage-operated calcium channels. 相似文献