全文获取类型
收费全文 | 655篇 |
免费 | 48篇 |
专业分类
林业 | 87篇 |
农学 | 32篇 |
基础科学 | 2篇 |
129篇 | |
综合类 | 41篇 |
农作物 | 11篇 |
水产渔业 | 51篇 |
畜牧兽医 | 285篇 |
园艺 | 12篇 |
植物保护 | 53篇 |
出版年
2023年 | 3篇 |
2022年 | 17篇 |
2021年 | 32篇 |
2020年 | 20篇 |
2019年 | 11篇 |
2018年 | 27篇 |
2017年 | 38篇 |
2016年 | 39篇 |
2015年 | 26篇 |
2014年 | 32篇 |
2013年 | 48篇 |
2012年 | 47篇 |
2011年 | 53篇 |
2010年 | 28篇 |
2009年 | 21篇 |
2008年 | 28篇 |
2007年 | 40篇 |
2006年 | 36篇 |
2005年 | 28篇 |
2004年 | 27篇 |
2003年 | 27篇 |
2002年 | 21篇 |
2001年 | 6篇 |
2000年 | 12篇 |
1999年 | 3篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1993年 | 3篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1971年 | 1篇 |
1969年 | 2篇 |
1968年 | 3篇 |
1967年 | 1篇 |
1913年 | 1篇 |
1906年 | 1篇 |
排序方式: 共有703条查询结果,搜索用时 46 毫秒
91.
Fabieli Pelissari Anderson Cleiton José Marco Aurélio Leite Fontes Antônio César Batista Matos Wilson Vicente Souza Pereira José Marcio Rocha Faria 《New Forests》2018,49(1):143-158
Knowledge of seed desiccation tolerance is fundamental for conservation and use of forest species. The protocol used for classification of seed desiccation tolerance and storage is time consuming and many times limited by the lack of information about optimum conditions for seed germination and treatments to overcome seed dormancy. This study evaluated 66 Brazilian tree species aiming to correlate seed characteristics with desiccation tolerance. For this purpose, a model was established to explain the relationship of tegument/seed mass ratio (SCR), seed mass, and water content of embryo + endosperm with desiccation tolerance. The principal component analysis showed the establishment of two groups, indicating the interaction between desiccation tolerance and seed characteristics. Recalcitrant seeds are more often associated with the water content of embryo + endosperm and water content of tegument + endocarp, while orthodox seeds are more associated with SCR and number of seeds per kilogram. The classification found using the model proposed was significantly correlated with desiccation tolerance and storage, with 92% confidence for the analyzed species. Seeds morphological characteristics can be used for prediction of desiccation tolerance and storage behavior; however, the use of a model that combines more variables increases the chance of accurate classification. 相似文献
92.
Ingrid Seynave Alain Bailly Philippe Balandier Jean-Daniel Bontemps Priscilla Cailly Thomas Cordonnier Christine Deleuze Jean-François Dhôte Christian Ginisty François Lebourgeois Dominique Merzeau Eric Paillassa Sandrine Perret Claudine Richter Céline Meredieu 《Annals of Forest Science》2018,75(2):48
Key message
The diversity of forest management systems and the contrasted competition level treatments applied make the experimental networks of the GIS Coop, a nationwide testing program in the field of emerging forestry topics within the framework of the ongoing global changes.Context
To understand the dynamics of forest management systems and build adapted growth models for new forestry practices, long-term experiment networks remain more crucial than ever.Aims
Two principles are at the basis of the experimental design of the networks of the Scientific Interest Group Cooperative for data on forest tree and stand growth (GIS Coop): contrasted and extreme silvicultural treatments in diverse pedoclimatic contexts.Methods
Various forest management systems are under study: regular and even-aged stands of Douglas fir, sessile and pedunculate oaks, Maritime and Laricio pines, mixed stands of sessile oak, European silver fir, and Douglas fir combined with other species. Highly contrasted stand density regimes, from open growth to self-thinning, are formalized quantitatively.Results
One hundred and eighty-five sites representing a total of 1206 plots have been set up in the last 20 years, where trees are measured regularly (every 3 to 10 years). The major outputs of these networks for research and management are the calibration/validation of growth and yield models and the drawing up of forest management guides.Conclusion
The GIS Coop adapts its networks so that they can contribute to develop growth models that explicitly integrate pedoclimatic factors and thus also contribute to research on the sustainability of ecosystems under environmental and socio-economic changes.93.
L. Shen A.H. Estrada E. Côté M.A. Powell B. Winter K. Lamb 《Journal of Veterinary Cardiology》2017,19(2):144-152
Introduction
To determine the relationship between aortoseptal angle (AoSA) and the short- and long-term systolic pressure gradient (PG) reduction following combined cutting and high-pressure balloon valvuloplasty (CB/HPBV) in dogs with severe subaortic stenosis.Animals
Retrospective study of 22 client-owned dogs of various breeds with severe subaortic stenosis (mean left ventricular to aortic PG = 143 mmHg; range = 80–322 mmHg) that underwent CB/HPBV.Materials and methods
Initial angiographic and left apical and right-sided parasternal long-axis view echocardiographic video loops were used for measuring the angle between the plane of the interventricular septum and the longitudinal axis of the ascending aorta. The PG reduction ratio immediately after CB/HPBV and 6 and 12 months later were compared with AoSA.Results
Weak correlations were observed for all instances of PG reduction ratio and AoSA type. Significantly greater mean differences of PG reduction ratio were observed for angles >160° than for angles <160° at 24 h (>160° mean: 54.45, standard error [SE]: ±3.8; <160° mean: 39.88, SE: ±2.09), 6 months (>160° mean: 57.73, SE: ±10.9; <160° mean: 28.22, SE: ±3.42), and 12 months (>160° mean: 76.11, SE: ±17.5; <160° mean: 27.61, SE: ±6.44; p=0.003).Conclusions
Dogs with AoSA >160° on right-sided parasternal long-axis view echocardiograms responded with a greater PG reduction following CB/HPBV than did dogs with AoSA <160°. This suggests that AoSA is associated with long-term outcomes of CB/HPBV, and measurement could help in the evaluation of dogs that are candidates for CB/HPBV. 相似文献94.
Rogério M. Borges Alcester Mendes Selene S. C. Nogueira Jérôme Bindelle Sérgio L. G. Nogueira-Filho 《Tropical animal health and production》2017,49(7):1353-1359
A nitrogen (N) balance digestion trial was conducted to determine the protein requirement of collared peccaries (Pecari tajacu). In a 4 × 4 Latin square design, four captive adult male peccaries were fed four isoenergy diets containing four different levels of N (11.7, 16.3, 22.8, and 26.7 g N/kg of dry matter—DM). After 15 days of adaptation, a total collection of feces and urine was carried out for five consecutive days. Regression analyses between N intake and N in feces and urine allowed to calculate the metabolic fecal nitrogen (MFN = 2.3 g N/kg of dry matter intake—DMI) and daily endogenous urinary N (EUN = 185 mg N/kg0.75). Likewise, by regression analyses between consumption of nitrogen and the nitrogen balance (NB = N ingested ? N excreted, mg N/kg0.75), a daily requirement of 514 mg N/kg0.75 was calculated. Therefore, if food intake is unrestricted, collared peccaries require a minimum in their diet of about 5.4% crude protein on DM basis. These values are almost as low as those found for browsing and frugivorous wild ruminants, which reinforce the proposition that peccaries’ digestive physiology is nearer to that of domestic and wild ruminants than domestic pigs. This relatively low protein requirement of collared peccary and its great ability to digest protein reveal the relevance of the forestomach for the species on nitrogen/protein metabolism and allow the use of diets with lower crude protein levels than the commercial ones used for the domestic pig, which reduces feed costs. 相似文献
95.
Carlos Alberto Scapim Cleso Antônio Patto Pacheco Antônio Teixeira do Amaral Júnior Rafael Augusto Vieira Ronald José Barth Pinto Thiago Vincenzi Conrado 《Euphytica》2010,174(2):209-218
In plant breeding, correlations between the statistics of stability and adaptability of popcorn cultivars are not yet well
understood. Therefore, the objectives of the present experiment was to investigate the correlations between sdi2 \sigma_{\rm di}^{2} and bi \beta_{\rm i} from Eberhart and Russell, ωi from Wricke,
\textS\texti(1) {\text{S}}_{\text{i}}^{(1)} ,
\textS\texti(2) {\text{S}}_{\text{i}}^{(2)} and
\textS\texti(3) {\text{S}}_{\text{i}}^{(3)} from Huehn, Pi from Lin and Binns and the rank-sum from Kang, and indicate the most reliable method for selecting popcorn cultivars. These
statistics were estimated by data of crop yield from 19 Brazilian genotypes under 21 environments and popping expansion under
16 environments. The ωi,
\textS\texti(1) {\text{S}}_{\text{i}}^{(1)} ,
\textS\texti(2) {\text{S}}_{\text{i}}^{(2)} ,
\textS\texti(3) {\text{S}}_{\text{i}}^{(3)} and sdi2 \sigma_{\rm di}^{2} were positively and significantly correlated indicating that just one in these five statistics is sufficient for selecting
stable genotypes although they were not correlated with the means of crop yield and popping expansion. The bi \beta_{\rm i} was negatively and significantly correlated with Pi for crop yield indicating that the most adaptable genotypes tend to have the lowest estimates of Pi. Although Pi was not correlated with ωi,
\textS\texti(1) {\text{S}}_{\text{i}}^{(1)} ,
\textS\texti(2) {\text{S}}_{\text{i}}^{(2)} ,
\textS\texti(3) {\text{S}}_{\text{i}}^{(3)} , or sdi2 \sigma_{\rm di}^{2} statistics, it displayed positive correlation with the Index 1 (crop yield and popping expansion +
\textS\texti(1) {\text{S}}_{\text{i}}^{(1)} rank) and Index 2 (crop yield and popping expansion + Wi) indicating that superior popcorn genotypes are also stable. Finally, both Pi and the rank-sum are useful statistics in breeding programmes where crop yield, popping expansion and stability are essential
traits for selecting genotypes. 相似文献
96.
Ghislain Vieilledent Benoît Courbaud Georges Kunstler Jean-François Dhôte 《Annals of Forest Science》2010,67(3):305-305
Question
Tree mortality can be modeled using two complementary covariates, tree size and tree growth. Tree growth is an integrative measure of tree vitality while tree diameter is a good index of sensitivity to disturbances and can be considered as a proxy for tree age which may indicate senescence. Few mortality models integrate both covariates because classical model calibration requires large permanent plot data-sets which are rare. How then can we calibrate a multivariate mortality model including size and growth when permanent plots data are not available?Location
To answer this question, we studied Abies alba and Picea abies mortality in the French Swiss and Italian Alps.Method
Our study proposes an alternative semi-parametric method which includes a random sample of living and dead trees with diameter and growth measurements.Results
We were able to calibrate a mortality model combining both size-dependent and growth-dependent mortality. We demonstrated that A. alba had a lower annual mortality rate (10%) than P. abies (18%) for low growth (< 0.2 mmyear?1). We also demonstrated that for higher diameters (DBH ≥ 70 cm), P. abies had a higher mortality rate (0.45%) than A. alba (0.32%).Conclusion
Our results are consistent with the mechanisms of colonization-competition trade-off and of successional niche theory which may explain the coexistence of these two species in the Alps. The method we developed should be useful for forecasting tree mortality and can improve the efficiency of forest dynamics models. 相似文献97.
Renato G Credie Francisco J Teixeira Neto Tatiana H Ferreira Antônio JA Aguiar Fabio C Restitutti José E Corrente 《Veterinary anaesthesia and analgesia》2010,37(3):240-249
ObjectiveTo investigate the effects of methadone on the minimum alveolar concentration of isoflurane (ISOMAC) in dogs.Study designProspective, randomized cross-over experimental study.AnimalsSix adult mongrel dogs, four males and two females, weighing 22.8 ± 6.6 kg.MethodsAnimals were anesthetized with isoflurane and mechanically ventilated on three separate days, at least 1 week apart. Core temperature was maintained between 37.5 and 38.5 °C during ISOMAC determinations. On each study day, ISOMAC was determined using electrical stimulation of the antebrachium (50 V, 50 Hz, 10 mseconds) at 2.5 and 5 hours after intravenous injection of physiological saline (control) or one of two doses of methadone (0.5 or 1.0 mg kg?1).ResultsMean (±SD) ISOMAC in the control treatment was 1.19 ± 0.15% and 1.18 ± 0.15% at 2.5 and 5 hours, respectively. The 1.0 mg kg?1 dose of methadone reduced ISOMAC by 48% (2.5 hours) and by 30% (5 hours), whereas the 0.5 mg kg?1 dose caused smaller reductions in ISOMAC (35% and 15% reductions at 2.5 and 5 hours, respectively). Both doses of methadone decreased heart rate (HR), but the 1.0 mg kg?1 dose was associated with greater negative chronotropic actions (HR 37% lower than control) and mild metabolic acidosis at 2.5 hours. Mean arterial pressure increased in the MET1.0 treatment (13% higher than control) at 2.5 hours.Conclusions and clinical relevanceMethadone reduces ISOMAC in a dose-related fashion and this effect is lessened over time. Although the isoflurane sparing effect of the 0.5 mg kg?1 dose of methadone was smaller in comparison to the 1.0 mg kg?1 dose, the lower dose is recommended for clinical use because it results in less evidence of cardiovascular impairment. 相似文献
98.
Phosphorus,total ammonia nitrogen and chlorophyll a from fish cages in a tropical lake (Lake Palminhas,Espirito Santo,Brazil)
下载免费PDF全文
![点击此处可从《Aquaculture Research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Graciele P Venturoti Alexandra C Veronez Rômulo V Salla Levy C Gomes 《Aquaculture Research》2016,47(2):409-423
Cage fish farming in natural and artificial lakes has become increasingly popular in recent years in tropical countries. The most commonly farmed tropical fish species is the Nile tilapia (Oreochromis niloticus L.). The aim of this study was to characterize the concentration of phosphorus, total ammonia nitrogen and chlorophyll a from existing fish farms (FF) in Lake Palminhas, located in Linhares/ES, Brazil. Three transects were drawn from 0 to 500 m from each of the four FF (FF1 to FF4) in the lake during six trials (three in the rainy season and three in the dry season). The lake presented a monomictic‐hot pattern, with stratification during the rainy season. Dilution of the monitored parameters did not occur sufficient over a distance of up to 500 m from the FF. The location of the FF in the lake and the input of N and P were critical to ensure optimal mixing conditions because the worst results was observed for the fish farm (FF1) located on a finger of the lake, where the highest concentrations of total phosphorus and chlorophyll a occurred. It was also noted that there was possible total phosphorus interference between FF3 and FF4. The results of this study demonstrate that Lake Palminhas had a low dilution power, and these findings may inform environmental assessments of cage fish farming in this region, providing instruments that may support environmental control of cage fish farming. 相似文献
99.
Daniela Flôres Isolda Cristina Haas Maria Cristina Canale Ivan Paulo Bedendo 《European journal of plant pathology / European Foundation for Plant Pathology》2013,135(2):237-242
Since its arrival in the British Isles in 1845 Phytophthora infestans has remained the most destructive pathogen of potato. In the ensuing period, the British and Irish P. infestans populations have undergone major displacements following the immigration of novel strains. Here we report the re-emergence of the Ib mitochondrial DNA haplotype in the British and Irish P. infestans populations associated with the 6_A1 genotype. Historically associated with the previously panglobally distributed clonal lineage US-1, the Ib haplotype has not been detected (with the exception of a single isolate in the mid 1990s) in the British or Irish P. infestans populations since the early 1980s. The 6_A1 isolates analysed possessed mtDNA Ib, but were otherwise quite unlike US-1, having the Pep allozyme genotype 96/96 and novel RG57 and SSR fingerprints. These genetic characteristics strongly suggest that the appearance of the 6_A1 genotype in these populations has resulted from migration (possibly after a recombination event elsewhere). This study highlights the advantages of utilising a range of different markers in pathogen monitoring. 相似文献
100.
Luciano Melo Eliane Silva Daniela Flôres José Ventura Hélcio Costa Ivan Bedendo 《European journal of plant pathology / European Foundation for Plant Pathology》2013,137(3):445-450
Papaya apical curl necrosis (PACN) has frequently been observed in several Brazilian states. Affected plants exhibit foliar chlorosis, curvature of the apex, shortening of the internodes leading to bunching of the crown leaves, necrosis of the young apical parts, leaf drop, and dieback. Naturally infected plants were sampled and subjected to PCR assays, which confirmed that a phytoplasma was associated with the disease. Sequencing of the 16S rRNA gene, conventional and computer-simulated RFLP analyses, and phylogenetic analysis allowed the determination of the PACN phytoplasma as a representative of a new subgroup, designated 16SrXIII-E. The phytoplasmas of various 16Sr groups, including 16SrI, 16SrII, 16SrX, 16SrXII, and 16SrXVII, are known to be involved in anomalies in papaya plants in several countries. However, the present study reports, for the first time, the occurrence of a 16SrXIII phytoplasma in association with a papaya disease. 相似文献