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991.
Polydisperse ethoxylated fatty alcohol (EFA) surfactants can improve the performance of crop protection agents. At the cuticular level they act as accelerators of penetration by increasing the mobility of active ingredients in the cuticle, the barrier properties of which are mainly caused by cuticular waxes. Polydisperse Genapol C-050 (GP C-050, average formula C12.5E5.8) was also found to increase mobility in wax-extracted polymer matrix membranes (MX) of bitter orange and pear, indicating that sorption of surfactants increased segmental mobility of polymethylene chains in cutin and wax. Sorption into MX of the active fraction of GP C-050 from 5g litre−1 micellar solutions was in equilibrium in less than 1 h after establishing contact. This is almost 100-fold faster than with cuticular membranes (CM). Temperature dependence of solute mobilities in CM was studied in order to measure activation energies (ED) of diffusion in the presence and absence of aqueous surfactant solutions. Monodisperse fatty alcohol ethoxylates C8E3, C8E4 and C12E6, and (non-surface-active) tributylphosphate decreased ED of the model compounds WL 110547 and bifenox in Citrus, Pyrus and Stephanotis CM by more than 100 kJ mol−1. This corresponds to 50 to 275-fold increases of mobilities at 15 °C. Our data suggest that the decrease in activation energies with the concomitant accelerating effect on mobility contributes considerably to the effects of so-called activator surfactants. High temperature and accelerators act similarly on barrier properties of CM. It is shown that effects of both monodisperse and polydisperse EFA surfactants on solute mobility are reversible and that radiolabelled C12E8 penetrated pear CM rapidly. However, rates of penetration were lowered by excess amounts of WL 110547 and especially phenylurea. Partition coefficients of seven organic solutes between Capsicum fruit cuticles and GP C-050 were very low and, with the exception of methylglucose, smaller than 1. They decreased with lipophilicity and differed about 100-fold. Especially for the lipophilic compounds they were orders of magnitude lower than octanol/water or cuticle/water partition coefficients, which indicates the limited usefulness of these values for an understanding of penetration of active ingredients from formulation residues. © 1999 Society of Chemical Industry 相似文献
992.
Ralph C Kirkwood 《Pest management science》1999,55(1):69-77
The plant cuticle is a highly complex membrane which forms the outer surface of the aerial portion of plants. The nature of the plant cuticle is reviewed with particular regard to its action as a potential barrier to the penetration of pesticide molecules; the role of the cuticular waxes is highlighted. The physicochemical properties of the cuticle influence the behaviour of spray droplets and, in turn, may affect the rate and efficiency of cuticle penetration. The permeation of active ingredients is influenced by their solubility characteristics as indicated by octanol/water (log Kow) and cuticle/water (Kcw) partition coefficients. Penetration of hydrophilic compounds (low log Kow) may be enhanced by hydration of the cuticle, while transcuticular transport of non-polar solutes (high log Kow) is increased by factors which reduce wax viscosity. The use of in-vitro models involving isolated cuticle membranes, isolated cuticle waxes, or isolated leaves has helped to focus on the activities of the cuticle in the absence of other physiological factors. Using these systems, the role of the waxes as a transport-limiting barrier has been identified and the factors influencing sorption, permeance and desorption examined. The action of surfactants, in vitro and in vivo, has been briefly addressed in regard to their role in facilitating cuticle penetration; other steps involving surfactant/solute/cuticle are complex, and synergy appears to depend on a number of factors including test species, concentration of active ingredient, surfactant type and concentration. Adjuvants may greatly influence the surface properties of the droplet, predispose the cuticle to solute transport, and enhance pesticide activity. The nature of these complex inter-relationships is discussed. © 1999 Society of Chemical Industry 相似文献
993.
Effects of droplet size and carrier volume on foliar uptake and translocation of gibberellic acid (GA3) and 2,4-D were investigated. Simulated spray droplets were applied to primary leaves of 10-day-old Phaseolus vulgaris (cv Nerina) in droplet sizes and carrier volumes ranging from 0.5 to 10 μl and 10 to 200 μl per leaf, respectively. Doses of GA3 (2 μg per leaf) and 2,4-D (100 μg per leaf) were held constant. Total uptake of GA3 approached a penetration equilibrium within 24 h after application, but uptake of 2,4-D continued to increase. Decreasing droplet size and/or increasing carrier volume increased GA3 and 2,4-D uptake. Translocation to stem and roots was positively related to total uptake. A positive linear relationship between the logarithm of the total droplet/leaf surface interface area and 2,4-D uptake or translocation was found, but for GA3 this relationship was quadratic. Potential mechanisms of the effects of spray application factors on foliar uptake are discussed. © 1999 Society of Chemical Industry 相似文献
994.
孙伯筠 《内蒙古农业大学学报(自然科学版)》2005,26(3):33-35
干寒地区金红苹果乔砧密植,不同密度、树型、株高、叶幕厚度,对树冠内光的水平分布和垂直分布密切相关。树冠内光照强度直接影响树体的花芽形成、开花坐果、果实的产量、质量。只有合理密植,才能充分利用光能,实现早果、丰产、优质。适宜的株行距为2m×4m,树高3.5m~4 m,树形为自由纺锤形。树体产量、质量形成集中分布于树冠外围1 m左右的范围,冠内相对光强在23%,是丰产优质的基线。 相似文献
995.
996.
The internal and external levels of topically applied soil insecticides, tefluthrin, terbufos and dieldrin, to 3rd-instar larvae of the southern corn rootworm, Diabrotica undecimpunctata howardi (Barber), were monitored over 48 h. Symptomology of poisoning with 10 times the dose of the larval 72-h LD90 for each chemical was observed over 48 h at various time points after treatment. Terbufos penetrated more rapidly than tefluthrin or dieldrin, although internal levels of tefluthrin and dieldrin had a longer-lasting plateau than terbufos. A 72-h LD30 treatment with tefluthrin resulted in faster penetration and also faster disappearance from the insect compared with the 10×72-h LD90 dose over a 48-h period. Recorded symptoms of poisoning included regurgitation of gut contents, defaecation and writhing and these are suggested to play an important part in voiding of the toxicants at lower (sub-lethal) treatment levels. The sub-lethal effects of tefluthrin are discussed with respect to likely pest behavioural changes, such as anorectic response, after field treatment of a crop. © of SCI. 相似文献
997.
黄河三角洲是胜利油田采油的主要区块,海床上分布有大量的输油管线。2005年8月6日至9日台风"麦莎"经过此地形成风暴潮。2005年8月5日和8月12日在风暴潮前后分别对胜利油田106钻井平台附近一条裸置海底管线铺设地区海床土工程性质进行了原位测量,并在管线拆除后于2006年9月5日对该地区进行了复测,发现:①由于管线的存在导致管线两侧潮滩的水动力条件发生改变,继而使得两侧海床土的性质发生了变化;②管线存在使得其影响区海床土强度增高,管线拆除后海床土强度降低均匀性变差;③风暴潮作用使海床土强度提高,均匀性增强。研究结果为波浪与管线共同作用下海床土变化研究提供典型实例。 相似文献
998.
999.
为了解温度和光照对强壮硬毛藻(Chaetomorpha valida)吸收营养盐效果的影响,探索其达到最佳吸收效果的环境条件,本文研究了该藻在不同温度(5、15、25℃)和光照[90 000、180 000、270 000μmol photons/(m2·s)]条件下对海水中常见营养盐成分的吸收效果。结果显示,强壮硬毛藻在5℃以上和90 000μmol photons/(m2·s)光照强度以上对水体中的NH4+-N、NO2--N和PO43--P都有较好的吸收效果,但温度和光照对强壮硬毛藻吸收营养盐均有显著影响,在设定范围内,营养盐吸收速率与温度和光照强度均呈正相关关系。极差分析结果显示,温度的影响大于光照强度的影响。方差分析结果显示,光照强度和温度的主效应都极显著,而且具有叠加效应,吸收率最高的条件为25℃/270 000μmol photons/(m2·s)组合,该条件下,NH4... 相似文献
1000.
在传统的促进森林天然更新(简称“促更”)方式的基础上,提出了深刻而确切的两种“促更”方式:焚烧方式和人工的较完全生土化方式,从理性上对这两种“促更”方式及技术要点做了较充分的阐释,并辅以国内外的部分佐证。建议通过设置试验点和林中探查两者密切相结合的具体办法,使“促更”作业技术臻于完善,使“促更”理论更加趋于成熟。 相似文献