全文获取类型
收费全文 | 324篇 |
免费 | 13篇 |
国内免费 | 1篇 |
专业分类
林业 | 23篇 |
农学 | 2篇 |
基础科学 | 4篇 |
102篇 | |
综合类 | 30篇 |
农作物 | 4篇 |
水产渔业 | 25篇 |
畜牧兽医 | 125篇 |
园艺 | 9篇 |
植物保护 | 14篇 |
出版年
2023年 | 3篇 |
2022年 | 3篇 |
2021年 | 6篇 |
2019年 | 3篇 |
2018年 | 4篇 |
2017年 | 6篇 |
2016年 | 7篇 |
2015年 | 3篇 |
2014年 | 6篇 |
2013年 | 16篇 |
2012年 | 9篇 |
2011年 | 15篇 |
2010年 | 16篇 |
2009年 | 14篇 |
2008年 | 16篇 |
2007年 | 12篇 |
2006年 | 13篇 |
2005年 | 12篇 |
2004年 | 12篇 |
2003年 | 8篇 |
2002年 | 10篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 3篇 |
1997年 | 5篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 6篇 |
1991年 | 9篇 |
1990年 | 4篇 |
1989年 | 8篇 |
1988年 | 3篇 |
1987年 | 8篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1972年 | 2篇 |
1971年 | 2篇 |
1969年 | 8篇 |
1968年 | 4篇 |
1967年 | 3篇 |
1939年 | 2篇 |
1919年 | 1篇 |
1913年 | 1篇 |
1911年 | 4篇 |
1909年 | 4篇 |
排序方式: 共有338条查询结果,搜索用时 0 毫秒
101.
102.
Rate of soil‐aggregate formation under different organic matter amendments—a short‐term incubation experiment 下载免费PDF全文
Rouven Andruschkewitsch Daniel Geisseler Stefan Dultz Rainer‐Georg Joergensen Bernard Ludwig 《植物养料与土壤学杂志》2014,177(2):297-306
To improve soil structure and take advantage of several accompanying ecological benefits, it is necessary to understand the underlying processes of aggregate dynamics in soils. Our objective was to quantify macroaggregate (> 250 μm) rebuilding in soils from loess (Haplic Luvisol) with different initial soil organic C (SOC) contents and different amendments of organic matter (OM) in a short term incubation experiment. Two soils differing in C content and sampled at 0–5 and 5–25 cm soil depths were incubated after macroaggregate destruction. The following treatments were applied: (1) control (without any addition), (2) OM1 (addition of OM: preincubated wheat straw [< 10 mm, C : N 40.6] at a rate of 4.1 g C [kg soil]–1), and (3) OM2 (same as (2) at a rate of 8.2 g C [kg soil]–1). Evolution of CO2 released from the treatments was measured continuously, and contents of different water‐stable aggregate‐size classes (> 250 μm, 250–53 μm, < 53 μm), microbial biomass, and ergosterol were determined after 7 and 28 d of incubation. Highest microbial activity was observed in the first 3 d after the OM application. With one exception, > 50% of the rebuilt macroaggregates were formed within the first 7 d after rewetting and addition of OM. However, the amount of organic C within the new macroaggregates was ≈ 2‐ to 3‐fold higher than in the original soil. The process of aggregate formation was still proceeding after 7 d of incubation, however at a lower rate. Contents of organic C within macroaggregates were decreased markedly after 28 d of incubation in the OM1 and OM2 treatments, suggesting that the microbial biomass (bacteria and fungi) used organic C within the newly built macroaggregates. Overall, the results confirmed for all treatments that macroaggregate formation is a rapid process and highly connected with the amount of OM added and microbial activity. However, the time of maximum aggregation after C addition depends on the soil and substrate investigated. Moreover, the results suggest that the primary macroaggregates, formed within the first 7 d, are still unstable and oversaturated with OM and therefore act as C source for microbial decomposition processes. 相似文献
103.
Ralf Balkenhol Bernard Ludwig Kristian Ufer Johannes Jochum Günther Friedrich 《植物养料与土壤学杂志》2001,164(3):283-288
Changes in mineral composition occurring in pyrite‐containing sediments under aerobic conditions are complex and not fully understood. The objective was to study the mineral formation and dissolution of silicates using ion activity product (IAP) calculations and x‐ray diffraction (XRD) on samples of different degrees of pyrite oxidation. Three sediment samples were obtained from the open‐cut brown coal mine of Zwenkau (Saxony, Germany) with low (ZL: 28 g kg—1), medium (ZM: 67 g kg—1) and high (ZH: 95 g kg—1) pyrite contents. These samples were oxidized in the laboratory for 3, 20, 67, and 130 days to obtain four different degrees of pyrite oxidation for each sediment. Sequential batch experiments were carried out for each sediment and oxidation status. Additionally, cation exchange capacities were determined. XRD showed the formation of gypsum (all sediments), jarosite (ZM, ZH), and rozenite (ZH) with increasing pyrite oxidation. IAP calculations suggested an occurrence of gypsum in all samples, of schwertmannite in slightly (ZH) and moderately oxidized (ZM, ZL) samples, and of alunite in a moderately oxidized sample (ZL). The contents of feldspar (ZL), mica/illite (ZL, ZH), and kaolinite (ZH) decreased with increasing pyrite oxidation. The cation exchange capacities of the sediments decreased by 20 (ZH) to 70 mmolc kg—1 (ZM). The change in mineral phases with increasing oxidation status of the sediments also changed the activities of Al, Fe, and SO4 in solution phases. The results obtained in this study suggested the usefulness of predictive models to estimate sediment and water acidification due to pyrite oxidation. 相似文献
104.
Kirtz G Meli M Leidinger E Ludwig P Thum D Czettel B Kölbl S Lutz H 《The Journal of small animal practice》2005,46(6):300-303
A diagnosis of Anaplasma phagocytophilum infection was confirmed in a two-year-old male golden retriever displaying few clinical and haematological abnormalities. This was achieved by demonstrating ehrlichial organisms in circulating neutrophils, by indirect immunofluorescence assay using A phagocytophilum as an antigen, and by detecting DNA specific for the 16S rRNA gene of granulocytic Anaplasma by PCR. After treatment with doxycycline for 10 days the dog showed improvement and the laboratory values returned to normal. 相似文献
105.
Ludwig C. A. Naegel 《Aquaculture International》1994,2(1):1-9
The integration of aquaculture into agricultural production systems to intensify profitable food production without the usual environmental degradation appears to be a promising option for a large number of small farmers in many developing countries. However, for the adoption of novel production systems, economic considerations are the main driving force. The farmer has to be convinced of the long- and short-term benefits and profits of different farming systems options. The potential farmer-aquaculturist needs site-specific holistic information packages of different production options, as contrasted with packages of technology only, in order to combine traditional knowledge with modern scientific results. These all-embracing data packages for different production systems must take into account the environmental conditions, the availability and price of the stocking material for aquaculture, of farm animals and seeds, seasonal farm and off-farm labour demands, and the socio-economic situation of the farmer and the neighbourhood. The possible production intensities, profits and risks have to be quantified, and the impacts on the environment, the family and society have to be determined. Such information would serve as a guideline for the selection of management options best suited to his/her farming system and would allow a choice of alternatives in case of unforeseen events. The multifaceted obstacles to developing a sustainable integrated aquafarming system are presented for a case in the Philippines. 相似文献
106.
107.
Susceptibility to antimicrobials of mastitis‐causing Staphylococcus aureus,Streptococcus uberis and Str. dysgalactiae from New Zealand and the USA as assessed by the disk diffusion test 下载免费PDF全文
108.
Bernard Ludwig Isabel Greenberg Michael Vohland Kerstin Michel 《European Journal of Soil Science》2023,74(4):e13394
Infrared spectroscopy in the visible to near-infrared (vis–NIR) and mid-infrared (MIR) regions is a well-established approach for the prediction of soil properties. Different data fusion and training approaches exist, and the optimal procedures are yet undefined and may depend on the heterogeneity present in the set and on the considered scale. The objectives were to test the usefulness of partial least squares regressions (PLSRs) for soil organic carbon (SOC), total carbon (Ct), total nitrogen (Nt) and pH using vis–NIR and MIR spectroscopy for an independent validation after standard calibration (use of a general PLSR model) or using memory-based learning (MBL) with and without spiking for a national spectral database. Data fusion approaches were simple concatenation of spectra, outer product analysis (OPA) and model averaging. In total, 481 soils from an Austrian forest soil archive were measured in the vis–NIR and MIR regions, and regressions were calculated. Fivefold calibration-validation approaches were carried out with a region-related split of spectra to implement independent validations with n ranging from 47 to 99 soils in different folds. MIR predictions were generally superior over vis–NIR predictions. For all properties, optimal predictions were obtained with data fusion, with OPA and spectra concatenation outperforming model averaging. The greatest robustness of performance was found for OPA and MBL with spiking with R2 ≥ 0.77 (N), 0.85 (SOC), 0.86 (pH) and 0.88 (Ct) in the validations of all folds. Overall, the results indicate that the combination of OPA for vis–NIR and MIR spectra with MBL and spiking has a high potential to accurately estimate properties when using large-scale soil spectral libraries as reference data. However, the reduction of cost-effectiveness using two spectrometers needs to be weighed against the potential increase in accuracy compared to a single MIR spectroscopy approach. 相似文献
109.
Miriam Fernanda Rodrigues José Miguel Reichert Jean Paolo Gomes Minella Leandro Dalbianco Rodrigo Luiz Ludwig Rafael Ramon Lilian Alessandra Rodrigues Norton Borges Júnior 《Journal of Soils and Sediments》2014,14(7):1311-1324
Purpose
Information on the effects of eucalyptus forests on hydrosedimentological processes is scarce, particularly at the catchment scale. Monitoring and mathematical modeling are efficient scientific tools used to address the lack of information for natural resource management and the representation and prediction of those processes. This study evaluates the effects of eucalyptus cultivation on hydrosedimentological processes in watersheds and to use the Limburg soil erosion model (LISEM) to represent and predict hydrological processes.Material and methods
The study was conducted in two forested watersheds: the main watershed (94.46 ha) and a nested sub-watershed (38.86 ha), both cultivated with eucalyptus and residual riparian native forest, located in southern Brazil. Hydrosedimentalogical monitoring was conducted from 16th February 2011 to 31st December 2012, and LISEM model calibrations were performed on the bases of six storms events.Results and discussion
The sediment yield for 2011 was 41.6 Mg km?2 and 38.5 Mg km?2 for the watershed and sub-watershed, respectively. An extreme event in 2012 provided greater sediment yield for the sub-watershed (99.8 Mg km?2) than that for the watershed (51.7 Mg km?2). Rainfall events with a greater maximum intensity generated rapid discharge and suspended sediment concentration responses in the sub-watershed due to the smaller drainage area and steeper landscape. In the main watershed, the accumulation of flood waves occurred for most events, with less steep hydrographs, and a later occurrence of the discharge peak after that of the sub-watershed. The LISEM adequately reproduced the peak discharge and runoff for the calibrated events; however, the peak time and the shape of the hydrograph were not adequately represented.Conclusions
The hydrosedimentological patterns of the watershed and sub-watershed, both cultivated with eucalyptus, was characterized by sedimentographs preceding hydrographs during rainfall–runoff events where scale effects occur, with maximum discharge and specific sediment yield greater in the watershed than that in the sub-watershed. Empirical models based on hydrologic variables may be used for estimating the suspended sediment concentration and sediment yield. Therefore, LISEM may be used for the prediction of hydrological variables in these forested watersheds. 相似文献110.
Arun K Shanker Scientist Ram Newaj P Rai KR Solanki K Kareemulla R Tiwari 《Archives of Agronomy and Soil Science》2013,59(3):281-291
An experiment was conducted by planting Hardwickia binata Roxb. at 200, 400 and 800 trees ha???1, intercrops viz., Brassica campestris (mustard) and Glycine max (soybean) were sown from the second year onwards in winter and summer respectively at the National Research Centre for Agroforestry, Jhansi, U.P., India with the objectives of evaluating agrosilvicultural potential of the system and to study the effect of tree densities on ecophysiology of understorey crops. Tree growth was affected by both density and intercrop in the initial years of growth. Photosynthetic photon flux density (PPFD) available to the intercrops reduced with increasing densities. Transpiration rate and stomatal conductance in intercrops decreased due to the presence of trees. No significant changes in leaf temperature were observed till the fifth year of the growing season. Yield was significantly higher in pure crop in comparison with all the densities in mustard. Soybean yield under 200 trees ha???1 was comparable to that of the pure crop. Trees at the density of 200 trees ha???1 provided a conducive microenvironment to the intercrops. 相似文献