全文获取类型
收费全文 | 2007篇 |
免费 | 91篇 |
国内免费 | 13篇 |
专业分类
林业 | 205篇 |
农学 | 57篇 |
基础科学 | 20篇 |
401篇 | |
综合类 | 251篇 |
农作物 | 93篇 |
水产渔业 | 147篇 |
畜牧兽医 | 695篇 |
园艺 | 46篇 |
植物保护 | 196篇 |
出版年
2023年 | 16篇 |
2022年 | 32篇 |
2021年 | 63篇 |
2020年 | 48篇 |
2019年 | 64篇 |
2018年 | 62篇 |
2017年 | 50篇 |
2016年 | 50篇 |
2015年 | 51篇 |
2014年 | 53篇 |
2013年 | 88篇 |
2012年 | 125篇 |
2011年 | 172篇 |
2010年 | 72篇 |
2009年 | 71篇 |
2008年 | 147篇 |
2007年 | 122篇 |
2006年 | 122篇 |
2005年 | 108篇 |
2004年 | 92篇 |
2003年 | 95篇 |
2002年 | 75篇 |
2001年 | 27篇 |
2000年 | 17篇 |
1999年 | 17篇 |
1998年 | 16篇 |
1997年 | 20篇 |
1996年 | 10篇 |
1995年 | 12篇 |
1994年 | 18篇 |
1993年 | 15篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 10篇 |
1989年 | 11篇 |
1988年 | 8篇 |
1987年 | 5篇 |
1986年 | 9篇 |
1985年 | 11篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1976年 | 5篇 |
1950年 | 5篇 |
1949年 | 4篇 |
1941年 | 4篇 |
排序方式: 共有2111条查询结果,搜索用时 15 毫秒
61.
Labruna MB McBride JW Camargo LM Aguiar DM Yabsley MJ Davidson WR Stromdahl EY Williamson PC Stich RW Long SW Camargo EP Walker DH 《Veterinary parasitology》2007,143(2):189-195
A molecular epidemiologic investigation in two Brazilian states (Rondônia and São Paulo) was undertaken to determine if Ehrlichia species responsible for human and animal ehrlichioses in North America could be found in Brazilian vectors, potential natural mammalian reservoirs and febrile human patients with a tick bite history. Samples, including 376 ticks comprising 9 Amblyomma species, 29 capybara (Hydrochaeris hydrochaeris) spleens, 5 canine blood, and 75 human blood samples from febrile patients with history of tick bites were tested by a real-time PCR assay targeting a fragment of the Ehrlichia dsb gene. Ehrlichia DNA was not detected in any tick, capybara or human samples. In contrast, 4 out of 5 dogs contained Ehrlichia canis DNA in their blood, which were sequenced, representing the first report of E. canis infecting dogs in the Amazon region of Brazil. Further studies are needed to evaluate the presence of other agents of human and animal ehrlichioses in Brazil. 相似文献
62.
The addition of the organosilicone surfactant ‘Silwet L77’ at 1-5 ml litre?1 to formulated glyphosate gave complete surface wetting on application to the adaxial leaf surface of perennial ryegrass (Lolium perenne L.). The wetting characteristics of the solution were associated with rapid foliar uptake and near maximal uptake in 3 h compared to greater than 5 h in the absence of ‘Silwet L77’. Evidence is presented showing that solutions containing ‘Silwet L77’ rapidly infiltrate stomata. Rapid uptake did not occur after application to the astomatous abaxial surface of perennial ryegrass leaves. The rapid rate of glyphosate uptake reduced the critical rainfall period to 2 h or less, compared to up to 10 h in the absence of ‘Silwet L77’. The use of ‘Silwet L77’ has major practical implications for the use of glyphosate in regions with unpredictable rainfall or high rainfall frequency. 相似文献
63.
Rice CC Kruger JM Venta PJ Vilnis A Maas KA Dulin JA Maes RK 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2002,16(3):293-302
Feline caliciviruses (FCVs) are potential etiologic agents in feline idiopathic lower urinary tract disease (I-LUTD). By means of a modified virus isolation method, we examined urine obtained from 28 male and female cats with nonobstructive I-LUTD, 12 male cats with obstructive I-LUTD, and 18 clinically healthy male and female cats. All cats had been routinely vaccinated for FCV. Two FCVs were isolated; I (FCV-U1) from a female cat with nonobstructive I-LUTD, and another (FCV-U2) from a male cat with obstructive I-LUTD. To determine the genetic relationship of FCV-U1 and FCV-U2 to other FCVs. capsid protein gene RNA was reverse transcribed into cDNA, amplified, and sequenced. Multiple amino acid sequence alignments and phylogenetic trees were constructed for the entire capsid protein, hypervariable region E, and the more conserved (nonhypervariable) regions A, B, D, and F. When compared to 23 other FCV isolates with known biotypes, the overall amino acid sequence identity of the capsid protein of FCV-U1 and FCV-U2 ranged from 83 to 96%; identity of hypervariable regions C and E ranged from 58 to 85%. Phylogenetically, FCV-U1 clearly separated from other FCV strains in phenograms based on nonhypervariable regions. In contrast, FCV-U2 consistently segregated with the Urbana strain in all phenograms. Clustering of isolates by geographic origin was most apparent in phenograms based on nonhypervariable regions. No clustering of isolates by biotype was apparent in any phenograms. Our results indicate that FCV-UI and FCV-U2 are genetically distinct from other known vaccine and field strains of FCV. 相似文献
64.
65.
Background
With the advancement of genotyping technologies, whole genome and high-density SNP markers have been widely used for genotyping of mapping populations and for characterization of germplasm lines in many crops. Before conducting SNP data analysis, it is necessary to check the individuals to ensure the integrity of lines for further data analysis.Results
We have developed an R package to conduct a parent-offspring test of individuals which are genotyped with a fixed set of SNP markers for further genetic studies. The program uses monomorphic SNP loci between parents and their progeny genotypes to calculate the similarity between each offspring and their parents. Based on the similarity of parents and individual offspring, the users can determine the threshold level for the individuals to be included for further data analysis. We used an F5-derived soybean population of ‘5601T’ x PI 157440 that was genotyped with 1,536 SNPs to illustrate the procedure and its application.Conclusions
The R package ‘ParentOffspring’ coupled with the available SNP genotyping platforms could be used to detect the possible variants in a specific cross, as well as the potential errors in sample handling and genotyping processes. It can be used in any crop which is genotyped with a fixed set of SNP markers.66.
There has been limited research on measuring potential differences in leaf gas exchange of Arracacha (Peruvian parsnip, Arracacia xanthorriza Bancroft) cultivars, as affected by different environments, as well as its relation to storage root-yield. The present paper reports field measurements of leaf CO2 assimilation rates (A) for five contrasting cultivars grown at two different high-altitude locations. Using a design of plots chosen at random with three repetitions, commercial root production was determined in the two locations at different altitude (1580 and 1930 m). Daily leaf gas exchange was repeatedly monitored with a portable open-mode infrared gas analyzer at different times in both locations during the growth cycle. Root-yield, leaf area and dry weight were measured. Significant differences in leaf photosynthetic rate and in specific leaf area (SLA) were observed among cultivars. Cultivars with high SLA, had high CO2 assimilation. Mean (An) and total (Atot) of CO2 assimilation and SLA were significantly correlated with storage root-yield across cultivars and locations. The three cultivars with the greatest commercial root production also had the highest maximum values for A and the highest specific leaf area, indicating that these two parameters can be used to select for highly productive cultivars of A. xanthorriza. 相似文献
67.
Nickolee Zollinger Roger Kjelgren Teresa Cerny-Koenig Kelly Kopp Rich Koenig 《Scientia Horticulturae》2006
Although low water use landscaping is becoming common in arid regions, little is known about drought tolerance and drought responses of many ornamental plants, especially herbaceous perennials. Drought responses were assessed for six herbaceous ornamental landscape perennials in a 38 l pot-in-pot system in northern Utah over a 2-year period. The first year was an establishment period. During the second year, drought responses were evaluated for established Echinacea purpurea (L.) Moench, Gaillardia aristata Pursh, Lavandula angustifolia P. Mill., Leucanthemum × superbum (J.W. Ingram) Berg. ex Kent, ‘Alaska’, Penstemon barbatus Roth var. praecox nanus rondo, and Penstemon × mexicali Mitch. ‘Red Rocks’. Plants were irrigated at frequencies of 1 (control), 2, or 4 weeks between June and September, simulating well-watered conditions, moderate drought, or severe drought. Osmotic potential (Ψs), gas exchange, visual quality, leaf area, and dry weight were assessed. In a confined root zone, P. barbatus showed the greatest tolerance to all levels of drought, avoiding desiccation by increasing root:shoot ratio and decreasing stomatal conductance as water became limiting. L. angustifolia and P. × mexicali showed tolerance to moderate drought conditions, but died after exposure to the first episode of severe drought. Neither G. aristata nor L. superbum were able to regulate shoot water loss effectively. Instead, both species displayed drought avoidance mechanisms, dying back when water was limiting and showing new growth after they were watered. Compared to control plants, G. aristata shoot dry weight was reduced by 50% and 84%, and L. superbum shoot dry weight was reduced by 47% and 99% for the 2- and 4-week irrigation intervals, respectively. Root dry weights were affected similarly for both species. E. purpurea exhibited poor visual quality at all irrigation intervals, in particular wilting severely in both drought treatments, but regaining turgor when watered again. P. barbatus is recommended for ornamental landscapes that receive little or no supplemental irrigation, while E. purpurea is not recommended for low water landscapes because of low visual quality under even mild drought. 相似文献
68.
We measured the seasonal and temperature responses of leaf photosynthesis and respiration of two co-occurring native New Zealand tree species with contrasting leaf phenology: winter-deciduous fuchsia (Fuchsia excorticata J. R. Forst & G. Forst) and annual evergreen wineberry (Aristotelia serrata J. R. Forst & G. Forst). There was no difference in the amount of nitrogen per unit leaf area (Narea, range 40-160 mmol m-2, P = 0.18) or specific leaf area (S, range 8-27 m2 kg-1, P = 0.87) in summer leaves of wineberry or fuchsia. The amount of nitrogen per unit leaf area and S varied significantly with height of leaves in the canopy for both species (r2 range 0.61-0.87). Parameters describing the maximum rates of rubisco carboxylation (Vcmax) and electron transport (Jmax) were related significantly to Narea, and were 60% higher on average in spring and summer leaves than in autumn and winter leaves for both species. The seasonal effect remained significant (P < 0.001) when Narea was included in a regression model, indicating that seasonal changes were not only due to changes in Narea. Values for Vcmax and Jmax were 30% lower in wineberry leaves than in fuchsia leaves on average, although the difference ranged from 15% in summer leaves to 39% in autumn leaves. Activation energies describing the temperature dependence of Vcmax and Jmax in wineberry were 111 and 114% of corresponding values for fuchsia (Ea (Vcmax) = 39.1 kJ mol-1, Ea (Jmax) = 32.9 kJ mol-1). Respiration at night was the same (P = 0.34) at 10 degrees C for both species (R10 = 0.7 micromol m-2 s-1), although activation energies (E0) were higher in wineberry than in fuchsia (47.4 and 32.9 kJ mol-1 K-1, respectively). These results show that rates of photosynthesis are higher in winter-deciduous fuchsia than in annual evergreen wineberry. 相似文献
69.
Bruno Vila Michel Vennetier Christian Ripert Olivier Chandioux Eryuan Liang Frédéric Guibal Franck Torre 《Annals of Forest Science》2008,65(7):709-709
70.
Bruno Vincent Fotini Koutroumpa Valérie Altemayer Géraldine Roux-Morabito Jeremy Gevar Carine Martin François Lieutier 《Annals of Forest Science》2008,65(1):111-111
As a consequence of the recent introduction of the pine wood nematode Bursaphelenchus xylophilus in Portugal, nematodes of the genus Bursaphelenchus were looked for in various French pine forests, in trees attacked by Monochamus galloprovincialis, the vector insect of B. xylophilus, and in the insects themselves. Trap trees were felled in 12 localities distributed all over the country. Nematodes were extracted from transversal stem discs; insects emerging from the trap trees were studied. B. hellenicus, B. leoni, B. mucronatus and B. sexdentati were isolated, but not B. xylophilus. The presence of B. mucronatus and the absence of B. xylophilus were confirmed by molecular markers. B. mucronatus was isolated from several regions with an average prevalence of 19%. The infestation of M. galloprovincialis by B. mucronatus reached 26.7%. The wide distribution of B. mucronatus in France could have an effect on the extension of B. xylophilus in a case of an introduction. 相似文献