全文获取类型
收费全文 | 518篇 |
免费 | 30篇 |
国内免费 | 2篇 |
专业分类
林业 | 62篇 |
农学 | 17篇 |
基础科学 | 1篇 |
155篇 | |
综合类 | 44篇 |
农作物 | 24篇 |
水产渔业 | 16篇 |
畜牧兽医 | 198篇 |
园艺 | 6篇 |
植物保护 | 27篇 |
出版年
2023年 | 6篇 |
2022年 | 2篇 |
2021年 | 12篇 |
2020年 | 12篇 |
2019年 | 18篇 |
2018年 | 17篇 |
2017年 | 14篇 |
2016年 | 11篇 |
2015年 | 12篇 |
2014年 | 26篇 |
2013年 | 32篇 |
2012年 | 32篇 |
2011年 | 44篇 |
2010年 | 12篇 |
2009年 | 24篇 |
2008年 | 28篇 |
2007年 | 27篇 |
2006年 | 30篇 |
2005年 | 33篇 |
2004年 | 27篇 |
2003年 | 27篇 |
2002年 | 22篇 |
2001年 | 9篇 |
2000年 | 5篇 |
1999年 | 6篇 |
1998年 | 5篇 |
1997年 | 1篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1973年 | 2篇 |
1971年 | 3篇 |
1970年 | 2篇 |
1968年 | 2篇 |
1928年 | 1篇 |
排序方式: 共有550条查询结果,搜索用时 15 毫秒
101.
102.
103.
Hydrothermal carbonization (HTC) is a method to produce carbonized material at relatively low temperatures (180–250 °C) under pressure and aqueous conditions. The product is called hydrochar and can be used as a soil amendment. However, applied in high dosages it may have detrimental effects on plants or soil biota. The potential impact of hydrochar amendment on beneficial soil organisms such as arbuscular mycorrhizal fungi (AMF) and earthworms and their interactions are not well understood. The goal of the present study was to determine effects of hydrochar on plant growth and soil biota and to evaluate interactions of earthworms and hydrochar on plant and AMF performance and to identify underlying mechanisms. In a greenhouse experiment, we investigated the effect of hydrochar at different addition rates (control, 1% and 10%, v/v) with or without the earthworm Aporrectodea caliginosa on the growth of Plantago lanceolata L. and the performance of its AMF. We observed a positive interaction between earthworms and 10% hydrochar on shoot and root biomass: added as a single treatment hydrochar had a negative effect on plant growth at this dosage, but plant biomass increased significantly when hydrochar was added together with earthworms. Root colonization by AMF increased significantly with increasing concentration of hydrochar, but was not affected by earthworms. Contrastingly, extraradical hyphal length of AMF was reduced by earthworms, but not affected by hydrochar. Thus, hydrochar and earthworms affected the performance of AMF, albeit of different AMF structures and in different directions. Our results indicate that earthworms may play an important role in alleviating the negative impacts of high dosages of hydrochar on plant growth; such interactions should move into focus of future research on potential effects of HTC materials. 相似文献
104.
Combined effects on soil microbial activity of nutrient and pesticide management in hybrid rice double annual cropping system were studied. Results of field experiment demonstrated significant changes in soil microbial biomass phospholipid contents,abundance of heterotrophic bacteria and proteolytic bacteria, electron transport system (ETS)/dehydrogenase activity, soil protein contents under different management practices and at various growth stages. Marked depletions in the soil microbial biomass phospholipid contents were found with the advancement of crop growth stages, while the incorporation of fertilizers and/or pesticides also induced slight changes, and the lowest microbial biomass phospholipid content was found with pesticides application alone. A decline in the bacterial abundance of heterotrophic bacteria and proteolytic bacteria was observed during the continuance of crop growth, while the lowest abundance of heterotrophic bacteria and proteolytic bacteria was found with pesticides application alone, which coincided with the decline of soil microbial biomass. A consistent increase in the electron transport system activity was measured during the different crop growth stages of rice. The use of fertilizers (NPK) alone or combined with pesticides increased it, while a decline was noticed with pesticides application alone as compared with the control.The soil protein content was found to be relatively stable with fertilizers and/or pesticides application at various growth stages in both crops undertaken, but notable changes were detected at different growth stages. 相似文献
105.
Gundolf Kohlmaier Luita Kohlmaier Elke Fries Wolfgang Jaeschke 《European Journal of Forest Research》2008,127(2):133-147
With the analytical tool, Frankfurt Harvested Wood Products Model, FPM, the carbon stocks and carbon stock changes of Harvested
Wood Products, HWP, either in USE or in LANDFILLS L-F, have been evaluated, each separately, from the readily available statistical
data base of the FAO, FAOSTAT, on the wood commodities: “Sawnwood and Wood-based Panels, SWP” and the paper commodities, “Paper
and Paperboard, PAP”. The focus was on the newly founded Asia-Pacific Partnership countries for Clean Development and Climate
(in short AP6), including Canada, which wants to join the AP6, in relation to the countries of the European Union EU-25. It
could be shown that the stocks and stock changes of the HWP in USE follow a simple algorithm of the annual consumption or
production and their mean annual growth, for the categories SWP and PAP, provided the mean residence times of the HWP in USE
can be estimated. With the information on the fraction of residues entering the landfills and their estimated residence times
an equivalent simple expression has been derived for stocks and stock changes of the HWP in LANDFILLS L-F. Their values have
been calculated to be approximately 0.5 to 0.7 times smaller than those of the HWP in USE. Still, all stock changes of the
HWP in L-F were positive and thus accumulating carbon. However, when methane outgasing within the HWP in L-F had been considered,
the calculated Greenhouse Gas Balance was zero or negative under the estimated parameters thus to at least partly compensate
the positive storage of carbon in HWP in USE. The percentage of CO2 removed by the HWP in USE in comparison to the annual greenhouse gas emissions varied from 0.3 to 1.7%, with a mean value
of 0.8% for the AP6 countries including Canada, in contrast to 1.0% of the EU-25 countries. Despite of the relative small
magnitude in relation to the total emission of all GHG this contribution should not be neglected in the GHG Budget of a country. 相似文献
106.
A. Thaler‐Neto R. Fries G. Thaller 《Zeitschrift für Tierzüchtung und Züchtungsbiologie》2000,117(3):153-167
The risk ratio (λR) is defined as ‘the recurrence risk for a relative of an affected individual divided by the prevalence in the general population’ and is considered as the most important parameter when designing mapping experiments for diseases in humans. In this paper, the risk ratio was introduced as a parameter to genetically characterize complex binary traits such as mastitis in cattle. Simulations were applied to evaluate the properties of λR under different genetic models (monogenic, digenic, polygenic and mixed models) and in dependency of their parameters for a design consisting of unbalanced halfsib families typically found in dairy cattle. Population prevalences of the simulated data ranged from 5 to 40% and λR was estimated on a phenotypic level. In the discrete loci models complexity of the traits was introduced through different levels of penetrance and the proportions of phenocopies within each genetic background. The risk ratio and the power to reject the null hypothesis of independent halfsibs (λR=1) were influenced by the prevalence in all genetic models chosen. Absolute values for λR were higher for lower prevalences, for example, λR=2.77 and 1.62 for a pure monogenic recessive model with 5 and 20% prevalence, respectively, whereas the power decreases in the case of lower prevalences. For all the prevalences investigated, higher risk ratios were found for discrete loci models compared with the polygenic models, with higher values for the monogenic relative to the digenic models in general. For the mixed models, λR was intermediate between the polygenic and discrete loci models. Genes with dominant relative to recessive inheritance for susceptibility caused higher risk ratios in monogenic and mixed models, for example, λR=5.16 and 2.77 for a pure monogenic model with 5% prevalence. In the discrete loci models, λR decreased with lower penetrance and a higher proportion of phenocopies. Risk ratios increased with the heritability in the polygenic and in addition with the effect of the major gene in mixed models. Consistent patterns of risk ratios were observed under the analysed genetic models and parameters, which indicate that the risk ratio is a parameter well suited to genetically characterize binary traits in unbalanced halfsib families. 相似文献
107.
Ingrid Allgoewer DVM Susanne Lucas DVM Stephan Albert Schmitz MD 《Veterinary radiology & ultrasound》2000,41(5):413-418
The magnetic resonance imaging appearance of the feline middle ear is described in three healthy cats and in five cats with middle ear disease. Owing to the good spatial resolution, multiplanar slice orientation as well as display high contrast resolution of soft tissue, in particular fluids, MR imaging was helpful prior to surgery. It is superior to radiography which failed to allow identification of the abnormality in two of our five cats. MR imaging for middle ear disease should include dorsal and transverse plane images using T1- and T2-weighted sequences. In the presence of a mass within the bulla or the external ear canal application of contrast medium is helpful. 相似文献
108.
XIEXiao-mei LIAOMin LIUWei-ping SusanneKLOSE 《水稻科学》2004,11(3):140-146
Combined effects on soil microbial activity of nutrient and pesticide management in hybrid rice double annual cropping system were studied. Results of field experiment demonstrated significant changes in soil microbial biomass phospholipid contents, abundance of heterotrophic bacteria and proteolytic bacteria, electron transport system (ETS)/dehydrogenase activity, soil protein contents under different management practices and at various growth stages. Marked depletions in the soil microbial biomass phospholipid contents were found with the advancement of crop growth stages, while the incorporation of fertilizers and/or pesticides also induced slight changes, and the lowest microbial biomass phospholipid content was found with pesticides application alone. A decline in the bacterial abundance of heterotrophic bacteria and proteolytic bacteria was observed during the continuance of crop growth, while the lowest abundance of heterotrophic bacteria and proteolytic bacteria was found with pesticides application alone, which coincided with the decline of soil microbial biomass. A consistent increase in the electron transport system activity was measured during the different crop growth stages of rice. The use of fertilizers (NPK) alone or combined with pesticides increased it, while a decline was noticed with pesticides application alone as compared with the control. The soil protein content was found to be relatively stable with fertilizers and/or pesticides application at various growth stages in both crops undertaken, but notable changes were detected at different growth stages. 相似文献
109.
Valeria Villanova Christian Galasso Giovanni Andrea Vitale Gerardo Della Sala Johan Engelbrektsson Niklas Strmberg Kashif Mohd Shaikh Mats X. Andersson Fortunato Palma Esposito Susanne Ekendahl Donatella De Pascale Cornelia Spetea 《Marine drugs》2022,20(7)
A local strain of Nannochloropsis granulata (Ng) has been reported as the most productive microalgal strain in terms of both biomass yield and lipid content when cultivated in photobioreactors that simulate the light and temperature conditions during the summer on the west coast of Sweden. To further increase the biomass and the biotechnological potential of this strain in these conditions, mixotrophic growth (i.e., the simultaneous use of photosynthesis and respiration) with glycerol as an external carbon source was investigated in this study and compared with phototrophic growth that made use of air enriched with 1–2% CO2. The addition of either glycerol or CO2-enriched air stimulated the growth of Ng and theproduction of high-value long-chain polyunsaturated fatty acids (EPA) as well as the carotenoid canthaxanthin. Bioassays in human prostate cell lines indicated the highest antitumoral activity for Ng extracts and fractions from mixotrophic conditions. Metabolomics detected betaine lipids specifically in the bioactive fractions, suggesting their involvement in the observed antitumoral effect. Genes related to autophagy were found to be upregulated by the most bioactive fraction, suggesting a possible therapeutic target against prostate cancer progression. Taken together, our results suggest that the local Ng strain can be cultivated mixotrophically in summer conditions on the west coast of Sweden for the production of high-value biomass containing antiproliferative compounds, carotenoids, and EPA. 相似文献
110.
Anna M. Johansson Maulik Upadhyay Erling Strandberg Susanne Eriksson 《Acta Agriculturae Scandinavica, Section A - Animal Sciences》2020,69(1-2):39-46
ABSTRACTThe Swedish Mountain (Fjäll) cattle and the subpopulation Fjällnära originates from northern Sweden. They are differentiated from both traditional and commercial cattle from southern Sweden. We analysed data from the GGP HD150k SNP array and investigated genetic diversity and differences between Fjäll and Fjällnära, and between different groups of Fjällnära. We found that the Fjällnära can be divided into four groups, which are differentiated from each other and from the other Fjäll cattle. We also compared allele frequencies between different groups of Fjäll and Fjällnära for some of the functional SNPs included in the SNP array. Interestingly, the B allele of Beta lactoglobulin has a very high frequency (94%) in the Fjällnära cattle, which is significantly different from the frequency in the Fjäll cattle (60%). Comparing older samples of Fjäll cattle with more recent samples, we found a significant increase in the frequency of the B allele in Fjäll cattle. 相似文献