全文获取类型
收费全文 | 436篇 |
免费 | 17篇 |
专业分类
林业 | 81篇 |
农学 | 12篇 |
基础科学 | 1篇 |
161篇 | |
综合类 | 43篇 |
农作物 | 14篇 |
水产渔业 | 5篇 |
畜牧兽医 | 95篇 |
园艺 | 3篇 |
植物保护 | 38篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 5篇 |
2020年 | 9篇 |
2019年 | 11篇 |
2018年 | 5篇 |
2017年 | 8篇 |
2016年 | 9篇 |
2015年 | 5篇 |
2014年 | 15篇 |
2013年 | 36篇 |
2012年 | 18篇 |
2011年 | 30篇 |
2010年 | 15篇 |
2009年 | 16篇 |
2008年 | 33篇 |
2007年 | 22篇 |
2006年 | 24篇 |
2005年 | 23篇 |
2004年 | 15篇 |
2003年 | 20篇 |
2002年 | 14篇 |
2001年 | 6篇 |
2000年 | 3篇 |
1999年 | 9篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 6篇 |
1993年 | 8篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1984年 | 2篇 |
1980年 | 2篇 |
1976年 | 5篇 |
1973年 | 2篇 |
1970年 | 2篇 |
1969年 | 2篇 |
1966年 | 4篇 |
1965年 | 4篇 |
1953年 | 2篇 |
1951年 | 2篇 |
1949年 | 2篇 |
1932年 | 5篇 |
1928年 | 2篇 |
1926年 | 1篇 |
排序方式: 共有453条查询结果,搜索用时 15 毫秒
161.
Spatial heterogeneity of soil properties and its mapping with apparent electrical conductivity 总被引:1,自引:0,他引:1
The site‐specific cultivation as part of the precision‐agriculture concept is more and more introduced into practical farming. However, soil information is often not available in a spatial resolution intrinsically needed for precision farming or other site‐specific soil use and management purposes. One approach to obtain spatially high‐resolution soil data is the non‐invasive measurement of the apparent electrical conductivity (ECa). In this study, we recorded the ECa on three fields with an EM38 (Geonics, Canada). The ECa data were compared with (1) ground truth data obtained by conventional drilling, (2) traditional soil maps (large scale, ≤1:5,000), (3) the growth and yield of corn. The temporal variability of the ECa due to varying soil moisture and temperature was taken into account by repeated measurements of the same fields and subsequent averaging of the ECa values. Significant correlations (r² = 0.76) were found between the mean weighted clay content (0–1.5 m) and the ECa. Furthermore, in soils with differently textured layers, ECa was used to estimate the thickness of the uppermost loess layer. A comparison of ECa and large‐scale soil maps reveals some pros and cons of ECa measurements. The main advantages of ECa recordings are the high spatial resolution in combination with low efforts. Yet, the ECa signal is no direct measure for a soil type or unit. Depending on the variability of substrates and layering, the ECa pattern can be a precise indicator for the spatial distribution of different soils. A strong conformity of the spatial variability of plant growth (derived from orthophotos and yield maps) and ECa patterns within a field indicates that the ECa signal per se—without conversion to traditional soil parameters—integrates the effects of various soil variables that govern soil fertility. Altogether, ECa surveys can be a powerful tool to facilitate and improve conventional soil mapping. 相似文献
162.
Mohsen HAMIDPOUR Maliheh KARAMOOZ Abdolreza AKHGAR Ahmad TAJABADIPOUR Gerhard FURRER 《土壤圈》2019,29(5):590-597
The mobility, bioavailability, and environmental fate of heavy metals in soil are controlled by their adsorption onto soil minerals and solid organic matter. The adsorption is strongly affected by the presence of various low-molecular-weight organic acids. In this study, effect of hydroxamate siderophore desferrioxamine B (DFOB) on cadmium (Cd) and zinc (Zn) adsorption onto two micaceous clay minerals, muscovite and phlogopite, was evaluated in batch experiments. Results showed that the presence of DFOB diminished the adsorption of Cd and Zn onto both minerals, particularly under neutral to alkaline pH conditions. For instance, at pH 8.2, the presence of DFOB caused a decrease in the adsorption of Zn onto phlogopite by nearly 50%. The equilibrium adsorption of Cd and Zn was satisfactorily described using Freundlich isotherm. The adsorption isotherms showed that the affinity of Cd and Zn onto the minerals decreased in the presence of DFOB. For example, at pH 8.0, the presence of siderophore caused a decrease in the Freundlich adsorption isotherm coefficient KF for Zn adsorption onto muscovite and phlogopite from 4.60 to 0.07 L g-1 and from 3.56 to 0.36 L g-1, respectively. These findings confirm the potential influence of siderophore on the fate of Cd and Zn in arid soils containing substantial contributions of micaceous silicate minerals. 相似文献
163.
Mid‐infrared spectroscopy (MIRS) has proven to be a cost‐effective, high throughput measurement technique for soil analysis. After multivariate calibration mid‐infrared spectra can be used to predict various soil properties, some of which are related to lime requirement (LR). The objective of this study was to test the performance of MIRS for recommending variable rate liming on typical Central European soils in view of precision agriculture applications. In Germany, LR of arable topsoils is commonly derived from the parameters organic matter content (SOM), clay content, and soil pH (CaCl2) as recommended by the Association of German Agricultural Analytical and Research Institutes (VDLUFA). We analysed a total of 458 samples from six locations across Germany, which all revealed large within‐field soil heterogeneity. Calcareous topsoils were observed at some positions of three locations (79 samples). To exclude such samples from LR determination, peak height at 2513 cm?1 of the MIR spectrum was used for identification. Spectra‐based identification was accurate for carbonate contents > 0.5%. Subsequent LR derivation (LRSPP) from MIRS‐PLSR predictions of SOM, clay, and pH (CaCl2) for non‐calcareous soil samples using the VDLUFA look‐up tables was successful for all locations (R2 = 0.54–0.82; RMSE = 857–1414 kg CaO ha?1). Alternatively, we tested direct LR prediction (LRDP) by MIRS‐PLSR and also achieved satisfactory performance (R2 = 0.52–0.77; RMSE = 811–1420 kg CaO ha?1; RPD = 1.44–2.08). Further improvement was achieved by refining the VDLUFA tables towards a stepless algorithm. It can be concluded that MIRS provides a promising approach for precise LR estimation on heterogeneous arable fields. Large sample numbers can be processed with low effort which is an essential prerequisite for variable rate liming in precision agriculture. 相似文献
164.
Lucas dos Santos Rodrigues Maria Grazia Pennino David Conesa Eidi Kikuchi Paul Gerhard Kinas Fabiana Gonçalves Barbosa Luís Gustavo Cardoso 《Fish and Fisheries》2023,24(1):159-175
Ecological niche models (ENMs) and species distribution models (SDMs) have been widely applied to various studies relevant to biogeography, conservation biology, and ecology. These modelling techniques seek to develop spatial maps for projecting, among others past, current, and future species distributions. Born in the field of terrestrial ecology, only in recent years have these models been applied to marine environmental issues, especially to improve the forecasting of the distribution of occurrences and capturing of fishery resources. This study aimed to present through bibliometric analysis the characteristics of articles related to the use of ENMs and SDMs in marine fishery resources considering three main points: (1) state of the art: number of articles over the years, journals, countries, collaborations, and focus of research; (2) characteristics linked to fishery resources: marine biogeographic realms, taxonomic groups, life phases, oceanographic zones, and behaviours; (3) characteristics linked to methods: type of method, type of biological and, environmental data. We provide a list of 378 articles (derived from 930 screened ones), the results, and a discussion of our findings, which represent a baseline for the current status (strengths, limits, and gaps) of the interface between ENMs/SDMs and fishery resources. 相似文献
165.
Effect of methionine sulphoximine on13 N-ammonium fluxes in the roots of barley and squash seedlings
13 N-Iabelled experiments were carried out with barley and squash seedlings to analyse the effect of methionine sulphoximine (MSO), as an inhibitor of the ammonium assimilation, on NH4+ fluxes in the roots at the level (150 μM NH4+) of the high affinity uptake system (HATS). MSO pretreatment in the root medium significantly accelerated NH4+ influx and efflux in NH4+ -fed plants of both species. Concomitantly, the level of NH4+ extracted from the root and shoot tissues was strongly elevated whereas the translocation of13 N-Iabelled organic substances (presumably amino products) into the shoots was markedly reduced. The onset of the increased NH4+ influx did not occur immediately but was indicated about 1 h after the application of MSO to the nutrient solution. Also, MSO did not directly affect the uptake of13 NO3?. The reason why MSO treatment leads to an acceleration of the NH4+ influx against an increasing level in the cell tissue remains obscure. In squash, an intermediate of NO3? metabolism is thought to suppress NH4+ uptake since NH4+ influx was high in N-free- and NH4+ -grown seedlings but was reduced about threefold in NO3? -fed squash plants; the suppression was not eliminated by MSO treatment. 相似文献
166.
Gerhard Weber 《Journal of pest science》1951,24(5):69-70
Ohne Zusammenfassung 相似文献
167.
Gerhard Creutz 《Journal of pest science》1950,23(3):46-47
Ohne ZusammenfassungPillniß 相似文献
168.
169.
Huber Dieterich Süchting G. von Kaufmann und H. Gerhard 《Forstwissenschaftliches Centralblatt》1949,68(9):626-634
Ohne Zusammenfassung 相似文献
170.