全文获取类型
收费全文 | 212篇 |
免费 | 14篇 |
专业分类
林业 | 36篇 |
农学 | 7篇 |
基础科学 | 6篇 |
49篇 | |
综合类 | 10篇 |
农作物 | 7篇 |
水产渔业 | 31篇 |
畜牧兽医 | 56篇 |
园艺 | 6篇 |
植物保护 | 18篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 8篇 |
2020年 | 9篇 |
2019年 | 16篇 |
2018年 | 18篇 |
2017年 | 11篇 |
2016年 | 13篇 |
2015年 | 7篇 |
2014年 | 13篇 |
2013年 | 10篇 |
2012年 | 12篇 |
2011年 | 18篇 |
2010年 | 8篇 |
2009年 | 8篇 |
2008年 | 8篇 |
2007年 | 7篇 |
2006年 | 7篇 |
2005年 | 12篇 |
2004年 | 1篇 |
2003年 | 4篇 |
2002年 | 2篇 |
2001年 | 1篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1985年 | 2篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 2篇 |
1970年 | 1篇 |
1969年 | 3篇 |
1962年 | 1篇 |
排序方式: 共有226条查询结果,搜索用时 15 毫秒
61.
Von Mark V. Cruz Richard Luhman Laura F. Marek Charlie L. Rife Randy C. Shoemaker E. Charles Brummer Candice A. C. Gardner 《Euphytica》2007,153(1-2):43-57
Flowering dates and life forms of all available Brassica napus accessions conserved at the North Central Regional Plant Introduction Station (NCRPIS) were characterized, and a survey of
molecular variation was conducted by using simple sequence repeats (SSR) in order to support better management of accessions
with diverse life forms. To characterize flowering phenology, 598 B. napus accessions from the NCRPIS collection were planted in Iowa and Kansas field sites together with a current commercial cultivar
and observed for days to flowering (first, 50% and 100% flowering) in 2003. Days from planting to 50% flowering ranged from
34 to 83 in Iowa and from 53 to 89 in Kansas. The mean accumulated growing degree days (GDD) to 50% flowering were 1,997 in
Iowa, and 2,106 in Kansas. Between locations, the correlation in flowering time (r = 0.42) and the correlation in computed GDD (r = 0.40) were both significant. Differences in flowering-time rank were observed for several accessions. Accessions that failed
to flower in Iowa in a single growing season comprised 28.5% of the accessions; of the flowering accessions, 100% plant flowering
was not always achieved. Accessions were grouped according to flowering time. A stratified sample of 50 accessions was selected
from these groups, including 10 non-flowering and 40 flowering accessions of diverse geographic origins and phenological variation.
The flowering time observed in the sampled accessions when grown in the greenhouse were found to be significantly correlated
to the flowering time observed in the field locations in Iowa (r = 0.79) and Kansas (r = 0.49). Thirty SSR markers, selected across 18 Brassica linkage groups from BrassicaDB, and 3 derived from Brassica expressed sequence tags (ESTs) were scored in the stratified sample. An average of three bands per SSR primer pair was observed.
Associations of SSR marker fragments with the life forms were determined. Analysis of molecular variation by using cluster
analysis and ordination resulted in recognizable, distinct groups of annual and biennial life-form types, which may have direct
applications for planning and management of future seed regenerations.
Mention of commercial brand names in this paper does not constitute an endorsement of any product by the U.S. Department of
Agriculture or cooperating agencies. 相似文献
62.
63.
Mariusz Czop Jacek Motyka Ondra Sracek Marek Szuwarzy��ski 《Water, air, and soil pollution》2011,214(1-4):423-434
The Gorka pit lake was formed in an inactive Jurassic limestone quarry after cessation of open-pit dewatering. The main problem of the water quality in this area is linked to a large volume of extremely alkaline leachate disposed in the flooded quarry. The lake is meromictic due to a large density contrast between shallow and deep water layers. Water in the lake is of the Na?CCO3?COH type, pH is in the range from 11.5 to 13.3, and there are high concentrations of sulfate and several toxic elements (Al, As, Cr, Mo, P, and V). The chemical composition of the extremely alkaline leachate was formed as a result of the groundwater interaction with the industrial red mud wastes containing 5?C10 wt.% of sodium carbonate. There is a trend of increasing concentrations and pH values with depth, mainly due to the in-gassing of atmospheric CO2 into the surface layer and due to density stratification in the water column. Similar stratification is observed in groundwater wells around the lake. High dissolved concentrations of oxyanionic contaminants such as As, Cr, and V are caused by their high mobility and desorption under extremely alkaline conditions. In spite of reducing conditions at the bottom of the lake, caused by high concentrations of dumped organic matter, sulfate behaves conservatively because sulfate reducing bacteria do not survive in this pH range. 相似文献
64.
Martin Kocour Otomar Linhart David Gela Marek Rodina 《Journal of the World Aquaculture Society》2005,36(1):103-113
The results of a 4-yr study focused on comparing growth performance in all-female and mixed-sex populations of common carp are presented. All-female and mixed-sex populations of purebred Northern mirror carp (M72) and scaly crossbreds of female Ropsha (ROP) and male/neomale M72 carp (ROP × M72) were used for this experiment. Average weight and survival after each growing season and slaughtering value after the third and fourth year of the study were measured. While after 8 wk of rearing no differences between all-female and mixed-sex populations were found, the 1-yr-old all-female mirror carp population (M72) gained 29.7% more weight ( P < 0.0001) than the mixed-sex (68.5:± 15.8 g against 52.8:± 13.9 g; meant S.D.) population. After the second, third and fourth year of rearing, live weight was 9.5% ( P = 0.0062) and 6.8% ( P = 0.0229) and insignificantly 5.1 % higher, respectively, in the all-female population. There was no significant difference, even after the fourth growing season, in live weight between all-females and bisexual scaly crossbreds (2,192 g± 478.3 and 2,206 g± 484.5, respectively). The percentage of the main edible parts (processed body, filleting yield) was significantly higher in both mirror and scaly, all-female populations at 3 yr of age but not significantly different in 4-yr-old fish. No distinct differences in survival and body shape of all-female and bisexual populations were found. The potential of all-female populations for commercial production is discussed. 相似文献
65.
Masternak Katarzyna Oko Sylwia Kamola Marek Ociepa Tomasz Nucia Aleksandra Kowalczyk Krzysztof 《European Journal of Forest Research》2022,141(4):617-628
European Journal of Forest Research - Increasing areas of gradation, making it difficult or impossible to perform restorations and forestations, and as causing tree crown damage, result in the need... 相似文献
66.
Sikorska E Gliszczyńska-Swigło A Khmelinskii I Sikorski M 《Journal of agricultural and food chemistry》2005,53(18):6988-6994
The study demonstrates the application of front face and right angle synchronous fluorescence spectroscopy for the characterization of edible oils. The method enables monitoring of tocopherols, pheophytins, and other fluorescent components in edible oils. Principal component analysis of synchronous fluorescence spectra revealed sample clustering according to the type of oil. Partial least-squares regression was utilized to develop calibration models between fluorescence spectra and total tocopherol content determined by HPLC. The regression models showed a good ability to predict tocopherol content. The best fitting results were obtained for 1% v/v diluted oils and for bulk samples using the entire spectrum, yielding the regression coefficient, r, of 0.991, and root mean square error of cross-validation of approximately 8%. The results presented confirm the capabilities of the fluorescence techniques as a tool for the analysis of edible oils. 相似文献
67.
? Context
Secondary Norway spruce forests in the Western Beskids are among the most damaged forests in Europe. Although spruce bark beetle (Ips typographus) has been recently causing large-scale damage to these forests, our understanding of I. typographus dynamics in this environment is inadequate for evaluating forest sustainability.? Aim
This study aims to evaluate the patterns of damage caused by I. typographus to spruce forests with compromised ecological stability.? Methods
Forest infestation by I. typographus was inferred from sanitary felling data collected from 1998 to 2004. Stand and site data were obtained from forest management plans. Spatial-dependence analysis, ordinary kriging and neural network-based regression modelling were used to investigate the patterns of infestation and the casual relationships in the studied ecosystem.? Results
I. typographus long-distance dispersal substantially decreased with outbreak culmination. The spread of infestation was only weakly related to stand and site parameters. Infestations spread isotropically at the stand and patch level but directionally at the regional scale.? Conclusions
The large-scale spread of infestation can be explained by the uniform age and species composition of the investigated forests and by the ability of populations to overwhelm suboptimal trees. The observations presented here suggest that secondary spruce forests in Europe may be unsustainable due to unprecedented bark beetle outbreaks, which can be further amplified by changing climate. 相似文献68.
Trine H Jensen Gitte Ajjouri Kurt J Handberg Marek J Slomka Vivien J Coward Martine Cherbonnel Véronique Jestin Peter Lind Poul H J?rgensen 《Acta veterinaria Scandinavica》2013,55(1):84
Background
Avian influenza virus (AIV) subtypes H5 and H7 attracts particular attention because of the risk of their potential pathogenicity in poultry. The haemagglutination inhibition (HI) test is widely used as subtype specific test for serological diagnostics despite the laborious nature of this method. However, enzyme-linked immunosorbent assays (ELISAs) are being explored as an alternative test method.H5 and H7 specific monoclonal antibodies were experimentally raised and used in the development of inhibition ELISAs for detection of serological response specifically directed against AIV subtypes H5 and H7. The ELISAs were evaluated with polyclonal chicken anti-AIV antibodies against AIV subtypes: H1N2, H5N2, H5N7, H7N1, H7N7, H9N9, H10N4 and H16N3.Results
Both the H5 and H7 ELISA proved to have a high sensitivity and specificity and the ELISAs detected H5 and H7 antibodies earlier during experimental infection than the HI test did. The reproducibility of the ELISA’s performed at different times was high with Pearson correlation coefficients of 0.96-0.98.Conclusions
The ELISAs are a potential alternative to the HI test for screening of large amounts of avian sera, although only experimental sera were tested in this study. 相似文献69.
Stloukal P Kucharczyk P Sedlarik V Bazant P Koutny M 《Journal of agricultural and food chemistry》2012,60(16):4111-4119
The preemergence chloroacetamide herbicide metazachlor was encapsulated in biodegradable low molecular weight poly(lactic acid) micro- and submicroparticles, and its release to the water environment was investigated. Three series of particles, S, M, and L, varying in their size (from 0.6 to 8 μm) and with various initial amounts of the active agent (5%, 10%, 20%, 30% w/w) were prepared by the oil-in-water solvent evaporation technique with gelatin as biodegradable surfactant. The encapsulation efficiencies reached were about 60% and appeared to be lower for smaller particles. Generally, it was found that the rate of herbicide release decreased with increasing size of particles. After 30 days the portions of the herbicide released for its highest loading (30% w/w) were 92%, 56%, and 34% for about 0.6, 0.8, and 8 μm particles, respectively. The release rates were also lower for lower herbicide loadings. Metazachlor release from larger particles tended to be a diffusion-controlled process, while for smaller particles the kinetics was strongly influenced by an initial burst release. 相似文献
70.
Vesely Tomas Neuberg Marek Trakal Lukas Szakova Jiřina Tlustoa Pavel 《Water, air, and soil pollution》2012,223(4):1847-1859
The effects of one of the most toxic heavy metals, lead (Pb), applied in two different concentrations and combined with chelate
application were investigated on the water macrophyte (Pistia stratiotes L.) physiology. The influences were observed by the chlorophyll and free amino acid content determination. Also the lead
accumulation in macrophyte biomass was investigated to assess the potential efficiency of this plant for rhizofiltration of
highly Pb-polluted water. Na EDTA and Na citrate were used as chelates and Pb(NO3)2 as lead supplement. The application of organic chelates simulated conditions of an induced phytoextraction process. Statistical
analyses were performed as a one-way ANOVA with a subsequent Tukey HSD test at a level of P < 0.05. Pb contents in both root and leaf tissues gradually increased with increasing Pb concentrations in the nutrient solution.
More lead was accumulated in leaves than in roots within all treatments. The total chlorophyll content decreased with increased
Pb concentration and with a higher content of chelates. The chelate addition increased the total amino acid content in leaves
but decreased the total amino acid content in roots. The addition of lead with chelates decreased the dry biomass weight.
However, water macrophyte showed extremely high lead accumulation in biomass in the short term (up to 8 days) and this accumulation
potential could be used for relatively fast and effective decrease of high concentration of this risk element in contaminated
water or sewage. 相似文献