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71.
BACKGROUND: In a screening programme for new agrochemicals from Chinese medicinal herbs, the essential oil of Atractylodes chinensis (DC.) Koidz was found to possess strong insecticidal activity against the common vinegar fly, Drosophila melanogaster L. The essential oil was extracted via hydrodistillation, and its constituents were determined by GC‐MS analysis. RESULTS: The main components of A. chinensis essential oil were β‐eudesmol (21.05%), β‐selinene (11.75%), γ‐elemene (7.16%) and isopetasam (5.36%). Bioactivity‐directed chromatographic separation on repeated silica gel columns led to the isolation of five compounds, namely atractylon, α‐elemol, β‐eudesmol, hinesol and β‐selinene. β‐Selinene, α‐elemol and hinesol showed pronounced contact toxicity against D. melanogaster adults, with LD50 values of 0.55, 0.65 and 0.71 µg adult?1 respectively. Atractylon and β‐eudesmol were also toxic to the fruit flies (LD50 = 1.63 and 2.65 µg adult?1 respectively), while the crude oil had an LD50 value of 2.44 µg adult?1. CONCLUSION: The findings suggested that the essential oil of Atractylodes chinensis and its active constituents may be explored as natural potential insecticides. Copyright © 2011 Society of Chemical Industry 相似文献
72.
不同含水率对谷子籽粒压缩力学性质与摩擦特性的影响 总被引:2,自引:7,他引:2
为了探明不同含水率谷子籽粒的物理机械性质,减少谷子籽粒在播种、碾米加工及储运等过程中受到压缩载荷及摩擦而产生的机械损伤,该文针对不同含水率的谷子籽粒进行压缩力学性质与摩擦特性试验。研究了谷子籽粒的挤压破碎过程,获得不同含水率谷子籽粒的力-位移(变形)曲线,破坏力、变形量及破坏能。随着含水率升高,破坏力减小,变形量和破坏能呈现先降低后升高的变化规律。同时采用赫兹接触理论,得到谷子籽粒单向表观弹性模量和许用挤压应力,结果表明二者都随含水率升高线性降低。分别测定了谷子籽粒与钢板和铝板间的滑动摩擦系数,随含水率升高,谷子与该2种材料的摩擦系数均增大,且与铝板的摩擦系数要高于钢板。根据试验结果,分别拟合得到了压缩和摩擦力学性能指标与谷子含水率的关系方程,为谷子播种、仓储、加工等装备设计及参数优化提供了基础依据。 相似文献
73.
该文通过对钵苗落差高度与栽植深度关系和秧苗钵体相对于导管不同材料的动、静摩擦系数的试验研究,为导管式分秧栽植机构的设计提供理论依据.试验结果表明:水稻钵体秧苗的栽植深度随钵苗落差高度的增加而增加;对一般水田土壤类型,在整地质量满足农艺要求的条件下,钵苗落差高度在0.75~1.50 m范围内时,秧苗栽植深度为4.8~12.5 mm,可以满足秧苗栽深的农艺要求;秧苗钵体相对于钢板和塑料板的摩擦系数变化不大,受秧苗钵体相对湿度的影响较大,且随钵体相对湿度的增加而增加,在相对湿度为80%左右时达到最大值;一般情况下,在机器设计中,可取摩擦系数的最大值为0.7,摩擦角为35°. 相似文献
74.
75.
The influence of soil structure on the degree of seed-soil contact within a seedbed is poorly understood. This paper presents a simple analogue of seed-soil contact which allows the examination of the influence of macroporosity and relative aggregate size on the degree of contact within a bed of deformable spheres. A method is described in which a rigid disc or sphere representing a seed is placed within a bed of deformable spheres of uniform size representing soil aggregates. The structure is then compressed uniaxially to a given macroporosity. Contact areas were measured by a technique involving the use of paint, dismantling of the sample, and image analysis. Results show that degree of contact increases as macroporosity decreases. Greatest levels of contact are achieved where rigid and deformable spheres are of similar size. This result appears to be a consequence of maximum stress concentration occurring at this size ratio. Contact points were unevenly distributed over the surface of the rigid sphere. The applicability of these findings is considered. 相似文献
76.
Jürgen Weber Jupp Kreutzmann Anita Plantikow Evelyn Claus Werner Manz Peter Heininger 《Journal of Soils and Sediments》2006,6(2):84-91
Goal, Scope and Background Numerous xenobiotics released into surface waters are transferred to suspended particulate matter and finally attached to
sediments. Aquatic organisms may be exposed to them by direct particle feeding, by physical contact with contaminated surfaces
as an exposure route, and by the uptake of dissolved contaminants after equilibration via the free water phase. In order to
assess potential sediment toxicity, each of these exposure routes has to be addressed. This paper presents a newly developed
particle contact assay that uses the fermentation performance of a specific Saccharomyces cerevisiae strain for the assessment
of toxic effects in sediments. The test procedure is based on the characteristic feature of growing yeast cells to attach
to sediment particles, which are also relevant for the accumulation of contaminants. The physical contact with lipophilic
contaminants mirrors an exposition pathway for the direct uptake into the cells. In order to quantitatively characterize the
toxic effects of particle attached pollutants on the fermentation performance, unpolluted native reference sediment was spiked
with representatives for widely distributed anthropogenic contaminants.
Methods Saccharomyces cerevisiae was established as sensitive eukaryotic microorganism for the ecotoxicological assessment of particle
attached anthropogenic contaminants in freshwater sediments. For this purpose, yeast cells were cultivated in sediment samples
and the resulting fermentation performance was continuously measured. Sediments artifically spiked with HCB, PCB, g-HCH, DDT,
and benzo(a)pyrene and solutions of each contaminant were comparatively investigated by means of their adverse effects on
yeast fermentation performance. Additionally, four native river sediments characterized by increasing levels of pollution
were assessed by the yeast particle contact assay, and simultaneously by standard aquatic tests with algae, daphniae, and
luminescent bacteria using pore water and elutriates. Results of the bioassays were related to specific sediment contamination
with respect to metals and organic priority pollutants.
Results and Discussion In sediments spiked with PCB and benzo(a)pyrene fermentation, performance was affected extensively below concentrations inhibiting
fermentation in contaminant solutions. This suggests a high efficiency of the exposure route by physical contact. The fermentation
performance was only slightly affected by single lipophilic pollutants, whereas mixtures of individually spiked sediments
caused critically reduced fermentation performance suggesting additive synergistic effects. Native river sediments modestly
to critically polluted by hazardous organic compounds lead to a slightly to dangerously reduced fermentation performance in
the yeast contact assay. These inhibitory effects were much less pronounced in the standard bioassays conducted with algae,
daphniae and luminescent bacteria, applying pore waters and elutriates as sample matrices. Using pore water, inhibition was
measured only in the most polluted sediment, elutriates lead to a slight inhibition of the algal growth in the undiluted sample
only. These results indicate an improved sensitivity of the yeast particle contact assay compared to the standard assays,
due to uptake and physical cell contact as additional routes of exposure.
Conclusion The yeast particle contact assay is a valuable tool for the assessment of ecotoxicological potential in freshwater sediments.
Since the assay addresses physical contact as an exposure route, it indicates bioavailability of lipophilic compounds in sediments.
Outlook The sensitive indication of bioavailable contaminants associated to sediment particles by the newly developed yeast particle
contact assay recommends it as a complementary microbial bioassay in a test battery for assessing major pathways of contaminants
in whole sediments. 相似文献
77.
为了比较土荆芥果实挥发油的熏蒸和触杀抑菌活性,测定了其对植物病原真菌菌丝生长和孢子萌发的熏蒸与触杀抑制作用,初步研究了其抑菌机制。结果表明,土荆芥果实挥发油对植物病原真菌具有强烈的抑制作用,熏蒸和触杀抑制作用均随着挥发油剂量增加而增强,随处理时间延长多呈减弱趋势。其对白菜黑斑病菌、小麦赤霉病菌、水稻胡麻斑病菌3种真菌菌丝生长的熏蒸和触杀抑制作用半数有效浓度(EC50)分别为17.4~22.1μL/L、103.9~241.7μL/L,对水稻胡麻斑病菌孢子萌发的熏蒸和触杀抑制作用EC50分别为28.8μL/L、789.3μL/L。土荆芥果实挥发油通过熏蒸方式作用于水稻胡麻斑病菌菌丝,使其细胞内含物渗漏;通过触杀方式作用于水稻胡麻斑病菌菌丝,随挥发油浓度升高和处理时间延长,相对电导率增加。GC-MS分析结果显示,土荆芥果实挥发油主要成分为2-蒈烯和驱蛔素。综合分析土荆芥果实挥发油的抑菌活性,熏蒸作用的效果优于触杀作用。 相似文献
78.
针对山地果园单向牵引式双轨运输机运行时存在钢丝绳松脱或断裂等问题,研制了一种摩擦制动装置,在描述载物滑车总体结构的基础上,重点分析了制动装置制动过程、关键结构的受力分析及台架制动测试试验.有限元分析表明,支撑柱的最大应力为6.3 MPa,最大位移为2.1×10-5 mm,且出现在支撑柱与摩擦片固定装置相连的螺栓截面上;轨道的最大应力为70.9 MPa,最大位移约为0.65 mm,且出现在直轨道与摩擦片接触面上,呈对称分布.台架试验结果表明,该制动装置的制动成功率为100%;高速摄影试验表明,随着装载质量的增大,制动时间及振幅均增加.该研究可为山地果园单向牵引式轨道运输机械的整机结构设计提供参考. 相似文献
79.
Effect of soil drying on mucilage exudation and its water repellency: a new method to collect mucilage 下载免费PDF全文
Mutez A. Ahmed Maire Holz Susanne K. Woche Jörg Bachmann Andrea Carminati 《植物养料与土壤学杂志》2015,178(6):821-824
Despite the importance of mucilage for soil–plant relations, little is known about the effect of soil drying on mucilage exudation. We introduce a method to collect mucilage from maize growing in wet and dry soils. Mucilage was collected from brace roots. The amount of mucilage exuded did not change with soil water content and transpiration rate. Mucilage exuded in dry soils had a higher degree of hydrophobicity, suggesting that the wetting properties of mucilage change in response to soil drying. 相似文献
80.
Based-on the new 8-bit microcontroller P89C51RD2 of PHILIPS company,the principal axis rotating speed of friction welding machine is controlled in closed loop by the system. That guarantee the stability of important parameter in friction welding.The design of software and hardware and the principle of the system is introduced detailedly.The output pulse of photo- coder is measured by using catching mode of P89C51RD2' PCA.And the D/A conversion is achieved by PWM pulse wide modulate mode of P89C51RD2' PCA also. With ISP function, the system program can be written or upgraded on-line and with long-distance.The whole circuit formed in module is very concision.The system runs well in practical production. 相似文献