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101.
Earthworms are the major component of the soil fauna in temperate agro-ecosystems. Land use and soil management are widely reported to influence earthworm populations. We report simple laboratory experiments in which earthworm survival was tested against uniaxial loads for a range of soil conditions. Across all the experimental conditions 86% of earthworms survived. While greater loads (up to 800 kPa) over longer exposure times (up to 60 s) decreased survival; even under the most severe test conditions 33% of earthworms survived. Our results suggest that decreased earthworm populations in compacted soil are not due to uniaxial loading alone, but may be the result of shearing the soil during loading or from changes to the soil properties. 相似文献
102.
Purpose
Air supply and soil moisture have significant impact on the decay time necessary for complete decomposition of an interred body. Concerning the general structure and hydraulic as well as pneumatic conditions, in many cases, a permeable refilled soil material surrounded by the undisturbed and less permeable soil outside the grave results in water ponding, less aerated conditions, and lower redox potential values within the grave. This reduces the decomposition speed or even leads to preservation of the entire body.Materials and methods
In order to ascertain soil structural processes and hydraulic properties in an earth grave within the first year after burial, a monitoring of soil redox and matric potentials was realized in newly refilled artificial (empty) graves. We surveyed four variations: undisturbed reference soil, soil backfill in artificial grave, soil backfill in artificial grave amended with 20 kg CaO m?3, and grave base and walls strewed with CaO. In the fourth artificial grave (soil backfill only), irrigation experiments were conducted in order to simulate the effects of grave maintenance on soil water budget. Pore size distribution, air conductivity, and saturated hydraulic conductivity were measured on soil core samples from the variations. The monitoring was realized with redox sensors and tensiometers in 50- and 130-cm depth in all four variations.Results and discussion
Soil structure disruption increased soil porosity but also favored saturation of the soil in context with precipitation events. Compared with the graves without amendment, the addition of quicklime resulted in higher air capacity and air permeability, saturated hydraulic conductivity, and a better-aerated (higher redox potentials) and less water-saturated soil. Non-recurring irrigation with 2.2, 4.4, and 8.9 mm did not affect the soil moisture in the 50- and 130-cm depth. Repeated irrigation with 8.9 mm on consecutive days led to persistent water saturation in the soil, especially in the 130-cm depth.Conclusions
The disturbed soil structure in the cover layer of an earth grave is sensitive to settlement and, together with a tendency to the development of stagnic conditions, this can have negative impact on soil aeration in the grave. Addition of quicklime to the soil enhances crack development in the base and walls of the grave, stabilizes the soil fragments in the backfill, and prevents intensive settlement processes. This reduces water ponding and leads to a better aeration of the soil. Irrigation of earth graves should be reduced to a minimum.103.
Effect of pore water pressure on tensile strength Direct tensile testing with measurements of the pore water suction was used to investigate the relationship between tensile strength and suction. The tests were conducted on a till and a clayey soil, both homogenized. A closer view is focused on the relationship between material strain and the development of suction. Beyond, the factor χ of the effective stress equation for unsaturated soils by Bishop (1959), which was calculated by the data of tensile strength and corresponding matric suction is compared to the volumetric χ of the tested soil specimens. It could be shown, that the pore water pressure changes with strain. Therefore, not the initial suction of a soil is relevant for its failure but the actual one that can be measured in the failure zone at the moment of fracture. In addition the application of the volumetric χ in the effective stress equation compared to the χ derived from tensile testing leads to an 1.6 to 2.8 fold overestimation of the contribution of matric suction to soil tensile strength. 相似文献
104.
Hard red winter wheat (Triticum aestivum L. emend. Thell.) is an important cool‐season winter forage used primarily for increasing weight gain on growing beef cattle in the southern Great Plains. ‘Karl’ hard red winter wheat grown alone or grown with either hairy vetch (Vicia villosa Roth) or pea [(Pisum sativum L. subsp. arvense) var. ‘Austrian winter'] was sampled for forage nutritive value. The interplanted legume forage was also sampled for forage nutritive value. Ruminally degradable nitrogen (RDN):ruminally degradable organic matter (RDOM) ratios were highest for legume forage and exceeded the National Research Council (NRC) recommendation of 26.13 g RDN: 1 kg RDOM for peak ruminai microbial efficiency during March, April, and May sample periods over the 2‐year study. Wheat grown alone met the NRC requirement only during March. Wheat grown with either hairy vetch or pea had higher (P<0.05) RDN:RDOM ratios and crude protein (CP) values when compared to wheat grown alone during May. There were no differences (P>0.05) in dry matter (DM) yield between wheat grown alone or grown with the legumes except when analyzed by individual date, and then only for 1 of 6 sample dates. Undegraded intake protein (UIP) was generally higher (PO.05) for wheat compared to the legumes and higher (PO.05) for wheat grown alone during May compared to wheat grown with the legumes during May. The decline of the RDN:RDOM values to 40% below the NRC recommendation of wheat grown alone during May indicates a possible need for protein supplementation for growing beef cattle grazing wheat during this period. These data also indicate that interplanting legumes with wheat may enhance animal performance by providing forage of higher nutritive value. More information regarding grazing tolerance of these selected cool‐season annual legumes and subsequent animal performance is required. 相似文献
105.
Ceramic suction probes were combined with internal redox electrodes in order to reduce the deviation between site parallels, and to relate redox potential measurements directly to the solution analyzed chemically. In a laboratory experiment soil material was water‐saturated for 49 days and temporal changes of redox potential and pH outside and inside the ceramic suction probes were recorded. Furthermore, iron concentrations inside the ceramic cups were detected. Results indicate that a device combining ceramic suction probes and redox electrodes is in principal possible. However, the device used here could not reduce the deviation between site replications compared to free installed redox electrodes. Increasing iron concentrations due to decreasing redox potentials outside and inside the ceramic suction probes indicate that the soil water iron dynamic is at least partly measurable using this device.<?show $6#> 相似文献
106.
Soils under loaded conditions may have different shrinkage behaviour from that of load‐free soils. In this study, we applied two kinds of mechanical stress (σ) on repacked homogeneous soil samples: transient and constant stresses, simulating the traffic load during tillage and the overburden pressure, respectively. Three transient stresses were applied on the soil surface with 150, 400 and 1400 kPa, while the constant stresses ranged from 1.8, 3.8, 5.5, to 7.3 kPa. We hypothesized that the two stresses play different roles in soil shrinkage behaviour as depicted by void ratio (e) and moisture ratio (?), as compared with load‐free soil. Thus, our aim was to build up the relationship between e, ? and σ. For a swelling soil, total pores can be divided into rigid and non‐rigid components according to their swelling and shrinkage capacity relative to soil moisture. The non‐rigid pores compacted by the transient stress can be regained in the subsequent wetting at load‐free conditions, whereas the compacted rigid pores do not recover. The reduction in rigid pores does not alter the soil pore shrinkage capacity. The shrinkage curves of transiently‐loaded soils are therefore parallel to each other with an identical coefficient of linear extensibility (COLE) and the same shrinkage slope, although their structural shrinkage phase narrows with an increase of stress. However, the constant stress compresses non‐rigid pores readily through suppressing their swelling capacity during wetting as well as compacting rigid pores. If the change of rigid pores is negligible, the shrinkage curves of constantly‐loaded soils converge at the zero shrinkage or the dry‐end point with the load‐free soil shrinkage. If the reductions of rigid and non‐rigid pores are both considered, the soil shrinkage combines the part of parallel shrinkage derived from the reduced rigid pores and the intersected shrinkage resulted from the altered non‐rigid pores. On the basis of different shrinkage behaviours resulting from the two mechanical stresses, we propose numerical formulae to illustrate a series of curves for the e‐?‐σ relationship. The different changes in rigid and non‐rigid pores cause soil water release differently. 相似文献
107.
108.
The 1994 eruption of Rabaul, in Papua New Guinea, involved a small plinian eruption at Vulcan and a vulcanian eruption on the opposite side of the caldera at Tavurvur. Vulcan's ash leachates indicate seawater interaction that is consistent with earlier observations of low sulfur dioxide emissions and the presence of ice crystals in the initial plinian eruption cloud. In contrast, Tavurvur ash leachates indicate no seawater interaction, and later sulfur dioxide emissions remained high despite low-level eruptive activity. Silicic melt inclusions indicate that the andesitic melt contained about 2 weight percent water and negligible carbon dioxide. Mafic melt inclusions in Tavurvur ash have water and carbon dioxide contents that vary systematically over the course of the eruption. The mafic melt inclusions suggest that a mafic dike intruded from below the silicic chamber and provide further evidence that mafic intrusions drive caldera unrest. 相似文献
109.
Excitability is generated in developing skeletal muscle by the incorporation of sodium-selective ion channels into the surface membrane. Whole-cell and patch voltage-clamp recording from myotubes and their embryologic precursors, myoblasts, indicated that voltage-activated sodium current in myoblasts was more resistant to block by tetrodotoxin (TTX) than that in myotubes. Single-channel recording from both cell types showed two classes of sodium channels. One class had a lower single-channel conductance, activated at more hyperpolarized voltages, and was more resistant to TTX than the other. The proportion of TTX-resistant to TTX-sensitive sodium channels was higher in myoblasts than in myotubes. Thus, the difference in TTX sensitivity between myoblasts and myotubes can be explained by a difference in the proportion of the two classes of sodium channels. In addition, the lower conductance of TTX-resistant channels provides insight into the relationship between the TTX binding site and the external mouth of the sodium channel. 相似文献
110.