全文获取类型
收费全文 | 9711篇 |
免费 | 531篇 |
国内免费 | 912篇 |
专业分类
林业 | 397篇 |
农学 | 768篇 |
基础科学 | 296篇 |
2977篇 | |
综合类 | 4032篇 |
农作物 | 886篇 |
水产渔业 | 414篇 |
畜牧兽医 | 854篇 |
园艺 | 378篇 |
植物保护 | 152篇 |
出版年
2024年 | 79篇 |
2023年 | 183篇 |
2022年 | 293篇 |
2021年 | 343篇 |
2020年 | 323篇 |
2019年 | 398篇 |
2018年 | 288篇 |
2017年 | 453篇 |
2016年 | 508篇 |
2015年 | 450篇 |
2014年 | 490篇 |
2013年 | 812篇 |
2012年 | 951篇 |
2011年 | 696篇 |
2010年 | 527篇 |
2009年 | 536篇 |
2008年 | 471篇 |
2007年 | 542篇 |
2006年 | 433篇 |
2005年 | 389篇 |
2004年 | 284篇 |
2003年 | 253篇 |
2002年 | 183篇 |
2001年 | 194篇 |
2000年 | 150篇 |
1999年 | 140篇 |
1998年 | 111篇 |
1997年 | 109篇 |
1996年 | 97篇 |
1995年 | 82篇 |
1994年 | 60篇 |
1993年 | 61篇 |
1992年 | 57篇 |
1991年 | 37篇 |
1990年 | 40篇 |
1989年 | 37篇 |
1988年 | 38篇 |
1987年 | 20篇 |
1986年 | 7篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1978年 | 4篇 |
1976年 | 1篇 |
1975年 | 6篇 |
1974年 | 2篇 |
1963年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
961.
Renu Pandey Krishna Kant Dubey Altaf Ahmad Rakshanda Nilofar Rachana Verma Vanita Jain 《Journal of plant nutrition》2015,38(8):1196-1217
Cultivars of Triticum aestivum, T. durum, and Secale cereale were grown at low (2 μM) and sufficient (500 μM) phosphorus (P) under ambient carbon dioxide (380 μmol mol?1; aCO2) and elevated CO2 (700 μmol mol?1, eCO2) to study responses of cereal species in terms of growth and P utilization efficiency (PUE) under P x CO2 interaction. Dry matter accumulation increased under eCO2 with sufficient P. Nevertheless, dry matter accumulated at eCO2 with low-P was similar to that obtained at aCO2 with sufficient P. Leaf area was 43% higher under eCO2 with sufficient P. Significant increase in lateral root density, length and surface area were noted at low-P under eCO2. Phosphorus use efficience (PUE) increased by 59% in response to eCO2 in low-P plants. Thus, eCO2 can partly compensate effect of low-P supply because of improved utilization efficiency. Among cereals, durum wheat was more suitable in terms of PUE under high CO2 and limiting P supply. 相似文献
962.
AbstractA column experiment was conducted to investigate the responses of root growth and phosphorus (P) efficiency among sweet potatoes—JiHei1 (JH1), NingZi2 (NZ2), SuShu11 (S11) and SuShu17 (S17)—under low P and normal P conditions. Root growth was inhibited by low P in root length and surface area across diameter classes, except for in S17. The P absorption was influenced and led to variations in P content among organs. A high correlation was observed in root dry matter (DM) and P uptake. The tuber DM declined among genotypes under low P, and different P efficiencies were determined. A higher phosphorus utilization efficiency was observed in S11 and S17, suggesting that more P was needed to maintain their normal growth. Physiological efficiency and phosphorus utilization efficiency were significantly positively correlated with the tuber DM, indicating that low P limited the growth of sweet potatoes. These results benefit the production and breeding of sweet potatoes in response to P deficiency. 相似文献
963.
964.
龙眼磷素营养诊断技术的研究 总被引:2,自引:1,他引:2
应用果园调查与大田磷肥施用试验相结合的方法 ,对龙眼磷素营养诊断技术进行了研究。结果表明 :土壤磷素诊断形态为速效磷 (Olsen法 ) ,其诊断指标 (mg/ kg)为 :>43 .89,丰富 ;1 7.5 7~ 43 .89,高 ;7.91~ 1 7.5 7,中 ;5 .0 0~ 7.91 ,低 ;<5 .0 0 ,极低。龙眼植株磷素营养诊断最佳诊断时期为 1月 ,最佳诊断部位为老熟秋梢第 2位叶 ,诊断形态为全磷 ,其诊断指标 (P% )为 :>0 .1 65 ,过剩 ;0 .1 2 4~ 0 .1 65 ,高 ;0 .1 0 9~ 0 .1 2 4,中 ;0 .0 80~ 0 .1 0 9,低 ;<0 .0 80 ,极低 相似文献
965.
Fungal decomposition of and phosphorus transformation from spruce litter needles (Picea abies) were simulated in systems containing litter needles inoculated with individual saprotrophic fungal strains and their mixtures. Fungal strains of Setulipes androsaceus (L.) Antonín, Chalara longipes (Preus) Cooke, Ceuthospora pinastri (Fr.) Höhn., Mollisia minutella (Sacc.) Rehm, Scleroconidioma sphagnicola Tsuneda, Currah & Thormann and an unknown strain NK11 were used as representatives of autochthonous mycoflora. Systems were incubated for 5.5 months in laboratory conditions. Fungal colonization in systems and competition among strains were assessed using the reisolation of fungi from individual needles. After incubation, needles were extracted with NaOH and extracts were analysed using 31P nuclear magnetic resonance spectroscopy (NMR). Needle decomposition was determined based on the decrease in C:N ratio. Systems inoculated with the basidiomycete S. androsaceus revealed substantial decrease in C:N ratio (from 25.8 to 11.3) while the effect of ascomycetes on the C:N ratio was negligible. We suppose that tested strains of saprotrophic ascomycetes did not participate substantially in litter decomposition, but were directly involved in phosphorus transformation and together with S. androsaceus could transform orthophosphate monoesters and diesters from spruce litter needles into diphosphates, polyphosphates and phosphonates. These transformations seem to be typical for saprotrophic fungi involved in litter needle decomposition, although the proportion of individual phosphorus forms differed among studied fungal strains. Phosphonate presence in needles after fungal inoculation is of special interest because no previous investigation recorded phosphonate synthesis and accumulation by fungi. Our results confirmed that the 31P NMR spectroscopy is an excellent instrumental method for studying transformations of soil organic phosphorus during plant litter decomposition. We suggest that polyphosphate production by S. androsaceus may contribute to the phosphorus cycle in forest ecosystems because this fungus is a frequent litter colonizer that substantially participates in decomposition. 相似文献
966.
Phosphatase activity in the rhizosphere and its relation to the depletion of soil organic phosphorus 总被引:23,自引:4,他引:23
Summary The distribution of phosphatase activity and of phosphate fractions of the soil in the proximity of roots was studied in order to evaluate the significance of phosphatases in P nutrition of various plants (Brassica oleracea, Allium cepa, Triticum aestivum, Trifolium alexandrinum). A considerable increase in both acid and alkaline phosphatase activity in all the four soil-root interfaces was observed. Maximum distances from the root surface at which activity increases were observed ranged from 2.0 mm to 3.1 mm for acid phosphatase and from 1.2 mm to 1.6 mm for alkaline phosphatase. The increase in phosphatase activity depended upon plant age, plant species and soil type. A significant correlation was noticed between the depletion of organic P and phosphatase activity in the rhizosphere soil of wheat (r = 0.99**) and clover (r = 0.97**). The maximum organic P depletion was 65% in clover and 86% in wheat, which was observed within a distance from the root of 0.8 mm in clover and 1.5 mm in wheat. Both the phosphatases in combination appear to be responsible for the depletion of organic P. 相似文献
967.
Summary Amino acids were extracted from fertility plots of a loamy sand soil with 0.05 M HF-HCl and with a 10% ethanol solution (free amino acids) and analysed by reverse-phase high performance liquid chromatography (HPLC). The total quantities of amino-N compounds analysed were 4.4 g/g soil for the acid treatment and 22.6 g/g soil for the 10% ethanol extract. Glycine and glutamic acid were the most abundant of 15 amino-N compounds in the HF-HCl extracts, whereas glutamic acid and ornithine + NH+
4 were found in the highest concentration in the 10% ethanol extracts. The HF-HCI pretreatment is used to increase the efficiency of the extraction of soil organic matter. Although this pretreatment removed some amino acids, the acids extract less than 1% of the total amino-N content of the crude soil extracts. The pretreatment, therefore, was not overly destructive. Comparisons between the amino acids extracted from the fertility plots were not conclusive, except for glycine, which was greater in concentration in the higher fertilizer N plots of the same crop rotation. 相似文献
968.
Interaction of the vesicular-arbuscular mycorrhizae of maize with extractable soil phosphorus levels and nitrogen-potassium fertilizers 总被引:1,自引:0,他引:1
Summary A field experiment was conducted for 3 years to determine whether increasing extractable soil P levels would affect vesicular-arbuscular mycorrhizae (VAM) of maize (Zea mays L.) and the subsequent uptake of P and production of dry matter. Five levels of extractable soil P were established on an Aquic Dystrochrept soil with high and low NK fertilization. The results show that as extractable soil-P levels increase the vesicular-arbuscular mycorrhizae of maize decrease, but P concentrations in both leaf and root tissue increase. There was a significant interaction between the extractable soil-P levels and NK treatment. At the low soil-P level NK fertilization increased mycorrhizae, while at the high soil-P levels NK fertilization reduced mycorrhizae. Dry-matter production generally paralleled extractable soil-P levels from 1.0 mg P kg–1 to a maximum at 10 mg P kg–1 soil (by ammonium acetate, pH 4.8). The reduction in vesicular-arbuscular mycorrhizae at the highest levels of extractable soil P apparently was not critical to either P uptake or dry-matter production.Scientific contribution No. 1196 Storrs Agricultural Experiment Station 相似文献
969.
Cut logs and high stumps of spruce, birch, aspen and oak - nine years of saproxylic fungi succession
Managed stands generally contain little coarse woody debris compared to natural forests. This study addresses the potential of retained cut wood to increase the amount of substrate available for a variety of saproxylic fungi.Fruit bodies of fungi were recorded from 270 cut high stumps and logs of spruce, birch, aspen and oak over nine years of initial succession. A total of 1565 occurrences of 148 species, seven of which were red-listed, were found. Numbers of species were significantly higher on logs than on stumps. Annual diversity peaked four to seven years after logging, sooner on logs than on stumps. Numbers of species were positively related to substrate diameter, but not to the level of shade/sun-exposure, while the presence of some individual species were significantly affected by one or both of these factors. Comparisons with data from the literature indicated no fundamental differences between fungal communities on cut wood and on naturally dead substrates. We conclude that cut wood left on site, especially logs, may mimic dead wood from trees that die swiftly from natural causes and support diverse fungal communities, both in shaded stands and in open logging sites. Substrates generated by slow self-thinning processes in natural forests however, are probably difficult to mimic in managed stands. 相似文献
970.